Prof. M. Ulema Manhattan College Computer Information Systems

Prof. M. Ulema Manhattan College Computer Information Systems
Business Data Communications and Networking 8th Edition Jerry Fitzgerald and Alan Dennis John Wiley & Sons, Inc Prof. M. Ulema Manhattan College Computer Information Systems Copyright 2005 John Wiley & Sons, Inc

Introduction to Data Communications
Chapter 1 Introduction to Data Communications Copyright 2005 John Wiley & Sons, Inc

Copyright 2005 John Wiley & Sons, Inc
Outline Brief history Communications, Information Systems and the Internet Data Communications Networks Network components, network types Network Models OSI model, Internet model, Layers Network Standards Standards making, common standards Future Trends Pervasive networking, integration of voice, video, and data, new information services Copyright 2005 John Wiley & Sons, Inc

Information Age First Industrial Revolution Introduction of machinery New organizational methods Changed the way people worked Second Industrial Revolution – Information Age Introduction of computers Introduction of networking and data communication Changed the way people worked again Faster communication  Collapsing Information lag Brought people together  Globalization Copyright 2005 John Wiley & Sons, Inc

Collapsing Information Lag
sped up the rate of transmission of information, Electronic communications telegraph 1900 1950 2004 1850 Information took days or weeks to be transmitted Information transmitted in minutes or hours huge quantities of information transmitted in a fraction of a second. growth of telecommunications and especially computer networks globalization phenomenon (WWW) Copyright 2005 John Wiley & Sons, Inc

Three Faces of Networking
Fundamental concepts of networking How data moves from one computer to another over a network Theories of how network operate Technologies in use today How theories are implemented, specific products How do they work, their use, applications Management of networking technologies Security Network Design Managing the network Copyright 2005 John Wiley & Sons, Inc

Advances in Phone Technology
1962 Telstar (Telecommunications via satellite), Fax services, digital transmission (T-carriers) first trans-continental and transatlantic phone connections 1915 1976 Packet-switched data communications 1876 Phone invented 1948 Microwave trunk lines (Canada) 1919 Strowger (stepper) switch, rotary dial phones (enabling automatic connections) 1969 Picturefone (failed commercially) 1984 Cellular telephone Copyright 2005 John Wiley & Sons, Inc

Invention to Regulation
1934 FCC established 1996 US Telecom Act 1968 Carterfone court decision allowing non-Bell CPE A time for technological change Regulation began in the USA (ICC) Phone invented (rapid acceptance) 1876 1900 millions of phones in use in the US 1885 AT&T Bell System: de facto monopoly 1910 1970 MCI wins court case; begins providing some long distance services 1984 Consent decree by US federal court Copyright 2005 John Wiley & Sons, Inc

1984 Consent Decree Divestiture: AT&T broken up into a long distance company (AT&T) & 7 Regional Bell Operating Companies (RBOCs) Deregulation: Competitive long distance (IXC) market; MCI & Sprint enter LD market (among others) Local Exchange Carrier (LEC) service markets remained under RBOC monopoly Copyright 2005 John Wiley & Sons, Inc

US Telecom Act of 1996 Replaced all current laws, FCC regulations, 1984 consent decree, and overrules state laws Main goal: open local markets to competition To date, though, local competition slow to take hold… Large IXCs expected to move into the local markets, happening only recently Likewise, RBOCs expected to move into long distance markets, happening only recently Copyright 2005 John Wiley & Sons, Inc

Worldwide Competitive Markets
Internet market Extremely competitive with more than 5000 Internet Service Providers (ISPs) in the US alone. Heavy competition in this area may lead to a shake out in the near future. World Trade Organization (WTO) agreement (1997) commitments by 68 countries to open, deregulate or lessen regulation in their telecom markets Multi-national telecom companies US companies offering services in Europe, South America European companies offering services in USA Copyright 2005 John Wiley & Sons, Inc

History of Information Systems
Online real-time, transaction oriented systems (replaced batch processing. DBMSs become common) PC LANs become common Batch processing mainframes 1950 1960 1990 2000 1970 1980 Data communications over phone lines (became common and mainframes became multi-user systems) PC revolution Networking everywhere Copyright 2005 John Wiley & Sons, Inc

NSFNet created as US Internet backbone
Internet Milestones NSFNet created as US Internet backbone 1986 1990 commercial access to the Internet begins Originally called ARPANET, the Internet began as a military-academic network 1969 Over 240 million servers and 400 million users 2001 ARPANET splits: Milnet - for military Internet - academic, education and research purposes only 1983 Government funding of the backbone ends 1994 Copyright 2005 John Wiley & Sons, Inc

Broadband Communications Copyright 2005 John Wiley & Sons, Inc
Datacom Basics Telecommunications transmission of voice, video, data, imply longer distances - broader term Data Communications movement of computer information by means of electrical or optical transmission systems convergence Broadband Communications Copyright 2005 John Wiley & Sons, Inc

Components of a Local Area Network
To other networks (e.g., Internet) Router Servers File Server HUB Client Computers Web Server Circuits Print Server Printer Copyright 2005 John Wiley & Sons, Inc

Network Types (based on Scale)
Local Area Networks (LANs) - room, building a group of PCs that share a circuit. Backbone Networks - less than few kms a high speed backbone linking the LANs at various locations. Metropolitan Area Networks (MAN) - (< few 10 kms) connects LANs and BNs at different locations leased lines or other services used to transmit data. Wide Area Networks (WANs) - (> few 10 kms) Same as MAN except wider scale Copyright 2005 John Wiley & Sons, Inc

Intranet vs. Extranet Intranet A LAN that uses the Internet technologies Open only those inside the organization Example: insurance related information provided to employees over an intranet Extranet Open only those invited users outside the organization Accessible through the Internet Example: Suppliers and customers accessing inventory information in a company over an extranet Copyright 2005 John Wiley & Sons, Inc

Implementation of Communications Functions
Single layer implemen-tation Applications OS Communication Applications OS Multi layer implementation Breaking down into smaller components Easier to implement Copyright 2005 John Wiley & Sons, Inc

Multi-layer Network Models
The two most important such network models: OSI and Internet Open Systems Interconnection Model Created by International Standards Organization (ISO) as a framework for computer network standards in 1984 Based on 7 layers Internet Model Created by DARPA originally in early 70’s Developed to solve to the problem of internetworking Based on 5 layers Based on Transmission Control Protocol/ Internet Protocol (TCP/IP) suite Copyright 2005 John Wiley & Sons, Inc

7-Layer Model of OSI Physical DataLink Network Transport Session Presentation Application Application Layer set of utilities used by application programs Presentation Layer formats data for presentation to the user provides data interfaces, data compression and translation between different data formats Session Layer initiates, maintains and terminates each logical session between sender and receiver Please Do Not Touch Steve’s Pet Alligator Copyright 2005 John Wiley & Sons, Inc

7-Layer Model of OSI Transport Layer deals with end-to-end issues such as segmenting the message for network transport, and maintaining the logical connections between sender and receiver Network Layer responsible for making routing decisions Data Link Layer deals with message delineation, error control and network medium access control Physical Layer defines how individual bits are formatted to be transmitted through the network Copyright 2005 John Wiley & Sons, Inc

Internet’s 5-Layer Model
Application Layer used by application program Transport Layer responsible for establishing end-to-end connections, translates domain names into numeric addresses and segments messages Network Layer - same as in OSI model Data Link Layer - same as in OSI model Physical Layer - same as in OSI model Physical DataLink Network Transport Application Please Do Not Touch Alligator * Copyright 2005 John Wiley & Sons, Inc

Comparison of Network Models
Copyright 2005 John Wiley & Sons, Inc

Message Transmission Using Layers
sender receiver Applications Applications A receiving layer wraps incoming message with an envelope Adds layer related addressing information A receiving layer removes the layer related envelope and forwards the message up Copyright 2005 John Wiley & Sons, Inc

Protocols Used by Network model layers Sets of rules to define how to communicate at each layer and how to interface with adjacent layers Layer N+1 Layer N+1 Layer N Layer N Layer N-1 Layer N-1 sender receiver Copyright 2005 John Wiley & Sons, Inc

Message Transmission Example

Important Points to Observe
Many different software packages (protocols) and many different packets (at different layers) Easy to develop new software Simple to change the software at any level Matching layers communicate at different computers Accomplished by standards e.g., Physical layer at the sending computer must be the same in the receiving computer Somewhat inefficient Involves many software layers and packet types Packet overhead (slower transmission, processing time) Copyright 2005 John Wiley & Sons, Inc

Standards Importance Provide a “fixed” way for hardware and/or software systems (different companies) to communicate Help promote competition and decrease the price Types of Standards Formal standards Developed by an industry or government standards-making body De-facto standards Emerge in the marketplace and widely used Lack official backing by a standards-making body Copyright 2005 John Wiley & Sons, Inc

Standardization Processes
Specification Developing the nomenclature and identifying the problems to be addressed Identification of choices Identifying solutions to the problems and choose the “optimum” solution Acceptance Defining the solution, getting it recognized by industry so that a uniform solution is accepted Copyright 2005 John Wiley & Sons, Inc

Major Standards Bodies
ISO (International Organization for Standardization) Technical recommendations for data communication interfaces Composed of each country’s national standards orgs. Based in Geneva, Switzerland ( ITU-T (International Telecommunications Union –Telecom Group Technical recommendations about telephone, telegraph and data communications interfaces Composed of representatives from each country in UN Based in Geneva, Switzerland ( Copyright 2005 John Wiley & Sons, Inc

Major Standards Bodies (Cont.)
ANSI (American National Standards Institute) Coordinating organization for US (not a standards- making body) IEEE (Institute of Electrical and Electronic Engineers) Professional society; also develops mostly LAN standards standards.ieee.org IETF (Internet Engineering Task Force) Develops Internet standards No official membership (anyone welcomes) Copyright 2005 John Wiley & Sons, Inc

Some Data Comm. Standards
Layer Common Standards 5. Application layer HTTP, HTML (Web) MPEG, H.323 (audio/video) IMAP, POP ( ) 4. Transport layer TCP (Internet) SPX (Novell LANs) 3. Network layer IP (Internet) IPX (Novell LANs) 2. Data link layer Ethernet (LAN) Frame Relay (WAN) PPP (dial-up via modem for MAN) 1. Physical layer RS-232c cable (LAN) Category 5 twisted pair (LAN) V.92 (56 kbps modem) Copyright 2005 John Wiley & Sons, Inc

Emerging Trends in Networking
Pervasive Networking Integration of Voice, Video and Data New Information Services Copyright 2005 John Wiley & Sons, Inc

Pervasive Networking Means “Network access everywhere” Exponential growth of Network use Many new types of devices will have network capability Exponential growth of data rates for all kinds of networking Broadband communications Use circuits with 1 Mbps or higher (e.g., DSL) Copyright 2005 John Wiley & Sons, Inc

Relative Capacities of Telephone, LAN, BN, WAN, and Internet Circuits.

Integration of Voice, Video & Data
Also called “Convergence” Networks that were previously transmitted using separate networks will merge into a single, high speed, multimedia network in the near future First step (already underway) Integration of voice and data Next Step Video merging with voice and data Will take longer partly due to the high data rates required for video Copyright 2005 John Wiley & Sons, Inc

New Information Services
World Wide Web based Many new types of information services becoming available Services that help ensure quality of information received over www Application Service Providers (ASPs) Develop specific systems for companies Providing and operating a payroll system for a company that does not have one of its own Information Utilities (Future of ASPs) Providing a wide range of info services ( , web, payroll, etc.) (similar to electric or water utilities) Copyright 2005 John Wiley & Sons, Inc

Implications for Management
Embrace change and actively seek to apply networks to improve what you do Information moved quickly and easily anywhere and anytime Information accessed by customers and competitors globally Use a set of industry standard technologies Can easily mix and match equipment from different vendors Easier to migrate from older technologies to newer technologies Smaller cost by using a few well known standards Copyright 2005 John Wiley & Sons, Inc

Copyright 2005 John Wiley & Sons, Inc.
All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publisher assumes no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information herein. Copyright 2005 John Wiley & Sons, Inc

Outline Application Architectures Host-Based, Client-Based, and Client-Server Architectures, Choosing Architectures World Wide Web How the Web Works, Inside an HTTP Request & HTTP Response Electronic Mail How Works, Inside an SMTP Packet Listserv, Attachments in MIME Other Applications Ftp, Telnet, Instant Messaging, Videoconferencing Copyright 2005 John Wiley & Sons, Inc

Application Layer - Introduction
Applications (e.g., , web, word processing) Application Layer Transport Layer Network Layer Functions of Applications Data storage Storing of data generated by programs (e.g., files, records) Data access logic Processing required to access stored data (e.g., SQL) Application logic Business logic Presentation logic Presentation of info to user and acceptance of user commands Copyright 2005 John Wiley & Sons, Inc

Application Architectures
Determined by how functions of application programs are spread among clients and servers Host-based Architectures Server performs almost all functions Client-based architectures Client performs most functions Client-server architectures Functions shared between client and server Copyright 2005 John Wiley & Sons, Inc

Host-Based Architectures
or a PC running a terminal emulation program captures key strokes then sends them to the mainframe displays information according to the server’s instructions Copyright 2005 John Wiley & Sons, Inc

Problems with Host-based Arch.
Host becoming a bottleneck All processing done by the host, which can severely limit network performance Upgrades typically expensive and “lumpy” Available upgrades require big jumps in processing and memory  $$$ Network demand grows more incrementally, so this often means a poor fit (too much or too little) between host performance and network demand. Copyright 2005 John Wiley & Sons, Inc

Client-Based Architectures
Example: Using a word processor on a PC and storing data (file) on a server Was popular in 1980s with the widespread use of PCs, LANs, and programs such as spreadsheets and word processors Copyright 2005 John Wiley & Sons, Inc

Problems with Client-Based Arch.
Data MUST travel back and forth between server and client Example: when the client program is making a database query, the ENTIRE database must travel to the client before the query can be processed Result in poor network performance Copyright 2005 John Wiley & Sons, Inc

Client-Server Architectures
(PC, mini, mainframe) Used by most networks today Client (PC) Example: Using a Web browser to get pages from Presentation logic Application logic Data Access logic Data Storage Application logic may reside on the client, server or be split up between the two Copyright 2005 John Wiley & Sons, Inc

Client-Server Architectures
Advantages More efficient because of distributed processing Allow hardware and software from different vendors to be used together Disadvantages Difficulty in getting software from different vendors to work together smoothly May require Middleware, a third category of software Copyright 2005 John Wiley & Sons, Inc

Middleware Middleware client application programs
a standard way of translating between software from different vendors Manages message transfers Insulates network changes from the clients ((e.g., adding a new server) Middleware server application programs Examples: Distributed Computing Environment (DCE) Common Object Request Broker Architecture (CORBA) Open Database Connectivity (ODBC) Copyright 2005 John Wiley & Sons, Inc

Multi-tier Architectures
Involve more than two computers in distributing application program logic 2-tier architecture (architectures discussed so far) 3-tier architecture 3 sets of computers involved N-tier architecture more than three sets of computers used Copyright 2005 John Wiley & Sons, Inc

Multi-tier Architectures
Advantages Better load balancing: More evenly distributed processing. (e.g., application logic distributed between several servers.) More scalable: Only servers experiencing high demand need be upgraded Disadvantages Heavily loaded network: More distributed processing  more exchanges Difficult to program and test due to increased complexity Copyright 2005 John Wiley & Sons, Inc

Fat vs. Thin Clients Depends on how much of the application logic resides on the client Fat client: (a.k.a., thick client) All or most of the application logic Thin client: Little or no application logic Becoming popular because easier to manage, (only the server application logic generally needs to be updated) The best example: World Wide Web architecture (uses a two-tier, thin client architecture) Copyright 2005 John Wiley & Sons, Inc

Thin-Client Example: Web Architecture
Web Server (PC, mini, mainframe) Client (PC) Presentation logic Application Logic Data Access logic Data Storage Copyright 2005 John Wiley & Sons, Inc

Criteria for Choosing Architecture
Infrastructure Cost Cost of servers, clients, and circuits Mainframes: very expensive; terminals, PCs: very inexpensive Development Cost Mainly cost of software development Software: expensive to develop; off-the-shelf software: inexpensive Scalability Ability to increase (or decrease) computing capacity as network demand changes Mainframes: not scalable; PCs: highly scalable; Server Farms highly scalable Copyright 2005 John Wiley & Sons, Inc

Choosing an Architecture
Host-Based Client-Based Client-Server Cost of Infrastructure High Medium Low Cost of Development Low Medium High Scalability Low Medium High Copyright 2005 John Wiley & Sons, Inc

World Wide Web Two central ideas: Hypertext A document containing links to other documents Uniform Resource Locators (URLs) A formal way of identifying links to other documents Invention of WWW (1989) By Tim Berners-Lee at CERN in Switzerland First graphical browser, Mosaic, (1993) By Marc Andressen at NCSA in USA; later founded Netscape CERN - Centre Européan pour Rechèrche Nucleaire NCSA - National Center for Supercomputing Applications Copyright 2005 John Wiley & Sons, Inc

How the Web Works Main Web communications protocol: Server Computer HTTP - Hypertext Transfer Protocol HTTP Request Client Computer HTTP Response A request-response cycle: include multiple steps since web pages often contain embedded files, such as graphics, each requiring a separate response. Clicking on a hyperlink or typing a URL into a browser starts a request-response cycle Copyright 2005 John Wiley & Sons, Inc

HTTP Request Message Request line Request header Request body
(command, URL, HTTP version number) required (If the user types in the URL by themselves, then the referring page is blank.) Request header (information on the browser, date, and the referring page ) optional Request body (information sent to the server, e.g., from a form) optional Copyright 2005 John Wiley & Sons, Inc

Example of an HTTP Request
Command URL HTTP version GET HTTP/1.1 Date: Mon 06 Aug :35:46 GMT User-Agent: Mozilla/6.0 Referer: Request Line Request Header URL that contained the link to the requested URL Web browser (code name for Netscape) Note that this HTTP Request message has no “Body” part. GMT – Greenwich Mean Time Copyright 2005 John Wiley & Sons, Inc

HTTP Response Message Response status Response header Response body
(http version number, status code, reason) optional Response header (information on the server, date, URL of the page retrieved, format used ) optional Response body (requested web page) required Copyright 2005 John Wiley & Sons, Inc

Example of an HTTP Response
Response Status HTTP/ OK Date: Mon 06 Aug :35:46 GMT Server: NCSA/1.3 Location: Content-type: text/html Response Header <html> <head> <title>Allen R. Dennis</title> </head> <body> <H2> Allen R. Dennis </H2> <P>Welcome to the home page of Allen R. Dennis</P> </body> </html> Response Body Another example of response status: HTTP/ page not found) Copyright 2005 John Wiley & Sons, Inc

HTML - Hypertext Markup Language
A markup language used to format Web pages Also developed at CERN (initially for text files – a subset of SGML) TAGs embedded in HTML documents include information on how to format the file Extensions to HTML needed to display multimedia files XML - Extensible Markup Language A new markup language for data Copyright 2005 John Wiley & Sons, Inc

Electronic Mail Heavily used Internet application Much, much faster than snail mail (regular mail) Extremely inexpensive (compared to $3-$10 per paper mail total avg. cost) Includes preparation, paper, postage, etc, Can substitute for other forms of communication, such as telephone calls Eliminates “telephone tag” users can answer at his/her convenience, instead of time of call Copyright 2005 John Wiley & Sons, Inc

Standards SMTP - Simple Mail Transfer Protocol Main standard for Originating user agent and the mail transfer agent Between mail transfer agents Originally written to handle only text files Usually used in two-tier client-server architectures Post Office Protocol (POP) and Internet Mail Access Protocol (IMAP) Main protocols used between the receiver user agent and mail transfer agent Main difference: with IMAP, messages can be left at the server after downloading them to the client Other competing standards Common Messaging Calls (CMC), X.400 Copyright 2005 John Wiley & Sons, Inc

Two-Tier E-mail Architecture
User agents (also called clients) Run on client computers Send to servers Download from mailboxes on those servers Examples: Eudora, Outlook, Netscape Messenger Mail transfer agents (also called mail server) Used by servers Send between servers Maintain individual mailboxes. Copyright 2005 John Wiley & Sons, Inc

How SMTP Works Server computer with server software SMTP packet Client computer (“message transfer agent”) with client software LAN reads the packet’s destination address and sends it over the Internet to the receiver’s mail server. SMTP packet (“user agent”) an message is sent as an SMTP packet to the local mail server Internet SMTP packet Server computer with IMAP or POP packet server software Client computer contacts the mail server which then downloads the message LAN stores the message in the receiver’s mail box SMTP packet Copyright 2005 John Wiley & Sons, Inc

Host Based e-mail Architectures
An old method used on UNIX (main-frame) based hosts Similar to client-server architecture, except Client PC replaced by a terminal (or emulator) Sends all keystrokes to the server Display characters received from the server All software resides on server Takes client keystrokes and understand user’s commands Creates SMTP packets and sends them to next mail server Copyright 2005 John Wiley & Sons, Inc

Three-Tier Client-Server Arch.
Best known example: Web based (e.g., Hotmail) Server computer with Web server software Server computer with server software Client computer with Web Browser sends HTTP requests to the Web server sends HTTP responses to the Web client translates the client’s HTTP requests into SMTP packets then send them to the Mail server performs the same functions as the mail server in the two-tier example No need for an user agent Copyright 2005 John Wiley & Sons, Inc

Web-based Server computer with Client computer with Web server software HTTP request LAN SMTP packet Server computer with Web browser server software HTTP response SMTP packet Internet SMTP packet Server computer with HTTP request server software Client computer with Web browser LAN IMAP or POP packet Server computer with HTTP response IMAP packet Web server software Copyright 2005 John Wiley & Sons, Inc

SMTP Message Header Body Attachments
(source and destination addresses, date, subject, and other information about the message) Body (message itself) Attachments (additional files included along with the message) Copyright 2005 John Wiley & Sons, Inc

Sample SMTP Message Text in “ “ are ignored From: “Alan TO: “Pat Someone” Date: Mon 06 Aug :03:02 GMT Subject: Sample Note Message-Id: DATA: This is an example of an message Header Body Unique ID used to keep track of messages. Note that this SMTP message has no attachments. Copyright 2005 John Wiley & Sons, Inc

MIME Multipurpose Internet Mail Extension A graphics capable mail transfer agent protocol (to send graphical information in addition to text) SMPT designed for text transfer only Included as part of an client Translates graphical information into text allowing the graphic to be sent as part of an SMTP message (as a special attachment) Receiver’s client then translates the MIME attachment from text back into graphical format Other Graphics capable mail agent protocols uuencode and binhex Copyright 2005 John Wiley & Sons, Inc

Listserv Discussion Groups
Mailing lists of users who join to discuss some special topic (e.g., cooking, typing, networking) Some permit any member to post messages, some are more restricted Parts of listserv Listserv Processor Process commands ( subscriptions, etc,) Listserv Mailer Receive a message and resend it to everyone To subscribe Send an to Listserv processor (address of the processor is different than the address of mailer) Copyright 2005 John Wiley & Sons, Inc

File Transfer Protocol (FTP)
Enables sending and receiving files over the Internet Requires an application program on the client computer and a FTP server program on a server Commonly used today for uploading web pages Many packages available using FTP WS-FTP (a graphical FTP software) FTP sites Closed sites Requires account name and password Anonymous sites Account name: anonymous; pwd: your address Copyright 2005 John Wiley & Sons, Inc

Telnet Allows one computer to log into other computers Remote login enabling full control of the host Requires an application program on the client computer and a Telnet server program on a server Client program emulates a “dumb” terminal Many packages available conforming Telnet EWAN Requires account name and password Anonymous sites Account name: anonymous; pwd: your address Copyright 2005 John Wiley & Sons, Inc

Instant Messaging (IM)
A client-server program that allows real-time typed messages to be exchanged Client needs an IM client software Server needs an IM server package Some types allow voice and video packets to be sent Like a telephone Examples include AOL, MSN, Yahoo and ICQ Two step process: Telling IM server that you are online Chatting Copyright 2005 John Wiley & Sons, Inc

How Instant Messaging Works
Client computer with IM packet When you type some text, your IM client sends the text in a packet to the IM server which relays it to your friend. client software LAN IM packet Server computer with sends a request to the IM server telling it that you are online. If a friend connects, the IM server sends a packet to your IM client and vice versa with IM server software LAN Internet IM packet Client computer with If a chat session has more than two clients, multiple packets are sent by the IM server. IM servers can also relay information to other IM servers. IM packet IM client software LAN Copyright 2005 John Wiley & Sons, Inc

Videoconferencing Provides real time transmission of video and audio signals among two or more locations Allows people to meet at the same time in different locations Saving money and time by not having to move people around (conference calling does the same thing) Traditionally involves 2 special purpose rooms with cameras and displays Desktop videoconferencing Low cost application linking small video cameras and microphones together over the Internet No need for special rooms Example: Net Meeting s/w on clients communicating through a videoconference server Copyright 2005 John Wiley & Sons, Inc

Videoconferencing Standards
Proprietary early systems Common standards in use today H.320 Designed for room-to-room videoconferencing over high-speed phone lines H.323 Family of standards designed for desktop videoconferencing and just simple audio conferencing over Internet MPEG-2 Designed for faster connections such as LAN or privately owned WANs Copyright 2005 John Wiley & Sons, Inc

Webcasting Special type of one-directional videoconferencing Content is sent from the server to users Process Content created by developer Downloaded as needed by the user Played by a plug-in to a Web browser No standards for webcasting yet Defacto standards: products by RealNetworks, Microsoft and Apple Copyright 2005 John Wiley & Sons, Inc

Network must be used to provide a worry-free environment for applications Network should not change the way an organization operates; application should! Network should enable wide variety of applications Dramatic increase in number and type of applications Rapid growth in amount and type of traffic Different implication on network design and management Increased operating cost Copyright 2005 John Wiley & Sons, Inc

Outline Circuits Configuration, Data Flow, Communication Media Digital Transmission of Digital Data Coding, Transmission Modes, Analog Transmission of Digital Data Modulation, Voice Circuit Capacity, Digital Transmission of Analog Data Pulse Amplitude Modulation, Voice Data Transmission, Instant Messenger Transmitting Voice Data Analog/Digital Modems Multiplexing FDM, TDM, STDM, WDM, Inverse Multiplexing, DSL Copyright 2005 John Wiley & Sons, Inc

Physical Layer - Overview
Includes network hardware and circuits Network circuits: physical media (e.g., cables) and special purposes devices (e.g., routers and hubs). Types of Circuits Physical circuits connect devices & include actual wires such as twisted pair wires Logical circuits refer to the transmission characteristics of the circuit, such as a T-1 connection refers to 1.5 Mbps Can be the same or different. For example, in multiplexing, one wire carries several logical circuits Network Layer Data Link Layer Physical Layer Copyright 2005 John Wiley & Sons, Inc

Types of Data Transmitted
Analog data Produced by telephones Sound waves, which vary continuously over time Can take on any value in a wide range of possibilities Digital data Produced by computers, in binary form, represented as a series of ones and zeros Can take on only 0 ad 1 Copyright 2005 John Wiley & Sons, Inc

Types of Transmission Analog transmissions Analog data transmitted in analog form (vary continuously) Examples of analog data being sent using analog transmissions are broadcast TV and radio Digital transmissions Made of square waves with a clear beginning and ending Computer networks send digital data using digital transmissions. Data converted between analog and digital formats Modem (modulator/demodulator): used when digital data is sent as an analog transmission Codec (coder/decoder): used when analog data is sent as a digital transmission Copyright 2005 John Wiley & Sons, Inc

Data Type vs. Transmission Type
Analog Transmission Digital Data Radio, Broadcast TV PCM & Video standards using codecs Digital Data Modem-based communications LAN cable standards Copyright 2005 John Wiley & Sons, Inc

Digital Transmission: Advantages
Produces fewer errors Easier to detect and correct errors, since transmitted data is binary (1s and 0s, only two distinct values)) Permits higher maximum transmission rates e.g., Optical fiber designed for digital transmission More efficient Possible to send more digital data through a given circuit More secure Easier to encrypt Simpler to integrate voice, video and data Easier to combine them on the same circuit, since signals made up of digital data Copyright 2005 John Wiley & Sons, Inc

Circuit Configuration
Basic physical layout of the circuit Configuration types: Point-to-Point Configuration Goes from one point to another Sometimes called “dedicated circuits” Multipoint Configuration Many computers connected on the same circuit Sometimes called “shared circuit” Copyright 2005 John Wiley & Sons, Inc

Point-to-Point Configuration
Used when computers generate enough data to fill the capacity of the circuit Each computer has its own circuit to any other computer in the network (expensive) Copyright 2005 John Wiley & Sons, Inc

Multipoint Configuration
Used when each computer does not need to continuously use the entire capacity of the circuit - Only one computer can use the circuit at a time + Cheaper (no need for many wires) and simpler to wire Copyright 2005 John Wiley & Sons, Inc

Data Flow (Transmission)
data flows move in one direction only, (radio or cable television broadcasts) data flows both ways, but only one direction at a time (e.g., CB radio) (requires control info) data flows in both directions at the same time Copyright 2005 John Wiley & Sons, Inc

Selection of Data Flow Method
Main factor: Application If data required to flow in one direction only Simplex Method e.g., From a remote sensor to a host computer If data required to flow in both directions Terminal-to-host communication (send and wait type communications) Half-Duplex Method Client-server; host-to-host communication (peer-to-peer communications) Full Duplex Method Half-duplex or Full Duplex Capacity may be a factor too Full-duplex uses half of the capacity for each direction Copyright 2005 John Wiley & Sons, Inc

Communications Media Physical matter that carries transmission Guided media: Transmission flows along a physical guide (Media guides the signal)) Twisted pair wiring, coaxial cable and optical fiber cable Wireless media (aka, radiated media) No wave guide, the transmission just flows through the air (or space) Radio (microwave, satellite) and infrared communications Copyright 2005 John Wiley & Sons, Inc

Twisted Pair (TP) Wires
Commonly used for telephones and LANs Reduced electromagnetic interference Via twisting two wires together (Usually several twists per inch) TP cables have a number of pairs of wires Telephone lines: two pairs (4 wires, usually only one pair is used by the telephone) LAN cables: 4 pairs (8 wires) Also used in telephone trunk lines (up to several thousand pairs) Shielded twisted pair also exists, but is more expensive Copyright 2005 John Wiley & Sons, Inc

Coaxial Cable (protective jacket ) Wire mesh ground Less prone to interference than TP (due to (shield) More expensive than TP (quickly disappearing) used mostly for CATV Copyright 2005 John Wiley & Sons, Inc

Fiber Optic Cable Light created by an LED (light-emitting diode) or laser is sent down a thin glass or plastic fiber Has extremely high capacity, ideal for broadband Works better under harsh environments Not fragile, nor brittle; Nit heavy nor bulky More resistant to corrosion, fire, etc., Fiber optic cable structure (from center): Core (v. small, 5-50 microns, ~ the size of a single hair) Cladding, which reflects the signal Protective outer jacket Copyright 2005 John Wiley & Sons, Inc

Types of Optical Fiber Multimode (about 50 micron core) Earliest fiber-optic systems Signal spreads out over short distances (up to ~500m) Inexpensive Graded index multimode Reduces the spreading problem by changing the refractive properties of the fiber to refocus the signal Can be used over distances of up to about 1000 meters Single mode (about 5 micron core) Transmits a single direct beam through the cable Signal can be sent over many miles without spreading Expensive (requires lasers; difficult to manufacture) Copyright 2005 John Wiley & Sons, Inc

Optical Fiber Excessive signal weakening and dispersion (different parts of signal arrive at different times) Center light likely to arrive at the same time as the other parts Copyright 2005 John Wiley & Sons, Inc

Wireless Media Radio Wireless transmission of electrical waves over air Each device has a radio transceiver with a specific frequency Low power transmitters (few miles range) Often attached to portables (Laptops, PDAs, cell phones) Includes AM and FM radios, Cellular phones Wireless LANs (IEEE ) and Bluetooth Microwaves and Satellites Infrared “invisible” light waves (frequency is below red light) Requires line of sight; generally subject to interference from heavy rain, smog, and fog Used in remote control units (e.g., TV) Copyright 2005 John Wiley & Sons, Inc

Microwave Radio High frequency form of radio communications Extremely short (micro) wavelength (1 cm to 1 m) Requires line-of-sight Perform same functions as cables Often used for long distance, terrestrial transmissions (over 50 miles without repeaters) No wiring and digging required Requires large antennas (about 10 ft) and high towers Possesses properties similar to light Reflection, Refraction, and focusing Can be focused into narrow powerful beams for long distance Copyright 2005 John Wiley & Sons, Inc

Satellite Communications
in a geosynchronous orbit A special form of microwave communications Signals sent from the ground to a satellite; Then relayed to its destination ground station Long propagation delay Due to great distance between ground station and satellite (Even with signals traveling at light speed) Copyright 2005 John Wiley & Sons, Inc

Factors Used in Media Selection
Type of network LAN, WAN, or Backbone Cost Always changing; depends on the distance Transmission distance Short: up to 300 m; medium: up to 500 m Security Wireless media is less secure Error rates Wireless media has the highest error rate (interference) Transmission speeds Constantly improving; Fiber has the highest Copyright 2005 John Wiley & Sons, Inc

Digital Transmission of Digital Data
Computers produce binary data Standards needed to ensure both sender and receiver understands this data Coding: language that computers use to represent letters, numbers, and symbols in a message Signaling (aka, encoding): language that computers use to represent bits (0 or 1) in electrical voltage Bits in a message can be send in A single wire one after another (Serial transmission) Multiple wires simultaneously (Parallel transmission) Copyright 2005 John Wiley & Sons, Inc

Coding A character  a group of bits Letters (A, B, ..), numbers (1, 2,..), special symbols (#, $, ..) Main character codes in use in North America ASCII: American Standard Code for Information Interchange Originally used a 7-bit code (128 combinations), but an 8-bit version (256 combinations) is now in use EBCDIC: Extended Binary Coded Decimal Interchange Code An 8-bit code developed by IBM Copyright 2005 John Wiley & Sons, Inc

Transmission Modes Parallel mode Uses several wires, each wire sending one bit at the same time as the others A parallel printer cable sends 8 bits together Computer’s processor and motherboard also use parallel busses (8 bits, 16 bits, 32 bits) to move data around Serial Mode Sends bit by bit over a single wire Serial mode is slower than parallel mode Copyright 2005 John Wiley & Sons, Inc

Parallel Transmission Example
Used for short distances (up to 6 meters) (since bits sent in parallel mode tend to spread out over long distances) (8 separate copper wires) Copyright 2005 John Wiley & Sons, Inc

Serial Transmission Example
Can be used over longer distances (since bits stay in the order they were sent) Copyright 2005 John Wiley & Sons, Inc

Signaling of Bits Digital Transmission Signals sent as a series of “square waves” of either positive or negative voltage Voltages vary between +3/-3 and +24/-24 depending on the circuit Signaling (encoding) Defines what voltage levels correspond to a bit value of 0 or 1 Examples: Unipolar, Bipolar RTZ, NRZ, Manchester Data rate: how often the sender can transmit data 64 Kbps  once every 1/64000 of a second Copyright 2005 John Wiley & Sons, Inc

Signaling (Encoding) Techniques
Unipolar signaling Use voltages either vary between 0 and a positive value or between 0 and some negative value Bipolar signaling Use both positive and negative voltages Experiences fewer errors than unipolar signaling Signals are more distinct (more difficult (for interference) to change polarity of a current) Return to zero (RZ) Signal returns to 0 voltage level after sending a bit Non return to zero (NRZ) Signals maintains its voltage at the end of a bit Manchester encoding (used by Ethernet) Copyright 2005 John Wiley & Sons, Inc

Manchester Encoding Used by Ethernet, most popular LAN technology Defines a bit value by a mid-bit transition A high to low voltage transition is a 0 and a low to high mid-bit transition defines a 1 Data rates: 10 Mb/s, 100 Mb/s, 1 Gb/s, .. 10- Mb/s  one signal for every 1/10,000,000 of a second (10 million signals (bits) every second) Less susceptible to having errors go undetected No transition  an error took place Copyright 2005 John Wiley & Sons, Inc

Digital Transmission Types
Unipolar Bipolar NRZ Bipolar RZ Manchester Copyright 2005 John Wiley & Sons, Inc

Analog Transmission of Digital Data
A well known example Using phone lines to connect PCs to Internet PCs generates digital data Phone lines use analog transmission technology Modems translate digital data into analog signals Internet M Telephone Network Phone line PC M Analog transmission Central Office (Telco) Digital data Copyright 2005 John Wiley & Sons, Inc

Telephone Network Originally designed for human speech (analog communications) only POTS (Plain Old Telephone Service) Enables voice communications between two telephones Human voice (sound waves) converted to electrical signals by the sending telephone Signals travel through POTS and converted back to sound waves Sending digital data over POTS Use modems to convert digital data to an analog format One modem used by sender to produce analog data Another modem used by receiver to regenerate digital data Copyright 2005 John Wiley & Sons, Inc

Sound Waves and Characteristics
Amplitude Height (loudness) of the wave Measured in decibels (dB) Frequency: Number of waves that pass in a second Measured in Hertz (cycles/second) Wavelength, the length of the wave from crest to crest, is related to frequency and velocity Phase: Refers to the point in each wave cycle at which the wave begins (measured in degrees) (For example, changing a wave’s cycle from crest to trough corresponds to a 180 degree phase shift). Copyright 2005 John Wiley & Sons, Inc

Wavelength vs. Frequency
speed = frequency * wavelength v = f λ v = 3 x108 m/s = 300,000 km/s = 186,000 miles/s Example: if f = 900 MHz λ = 3 x108 / 900 x 10 3 = 3/9 = 0.3 meters λ Copyright 2005 John Wiley & Sons, Inc

Modulation Μodification of a carrier wave’s fundamental characteristics in order to encode information Carrier wave: Basic sound wave transmitted through the circuit (provides a base which we can deviate) Βasic ways to modulate a carrier wave: Amplitude Modulation (AM) Also known as Amplitude Shift Keying (ASK) Frequency Modulation (FM) Also known as Frequency Shift Keying (FSK) Phase Modulation (PM) Also known as Phase Shift Keying (PSK) Copyright 2005 John Wiley & Sons, Inc

Amplitude Modulation (AM)
Changing the height of the wave to encode data One bit is encoded for each carrier wave change A high amplitude means a bit value of 1 Low amplitude means a bit value of 0 More susceptible noise than the other modulation methods Copyright 2005 John Wiley & Sons, Inc

Frequency Modulation (FM)
Changing the frequency of carrier wave to encode data One bit is encoded for each carrier wave change Changing carrier wave to a higher frequency encodes a bit value of 1 No change in carrier wave frequency means a bit value of 0 Copyright 2005 John Wiley & Sons, Inc

Phase Modulation (PM) Changing the phase of the carrier wave to encode data One bit is encoded for each carrier wave change Changing carrier wave’s phase by 180o corresponds to a bit value of 1 No change in carrier wave’s phase means a bit value of 0 Copyright 2005 John Wiley & Sons, Inc

Concept of Symbol Symbol: Each modification of the carrier wave to encode information Sending one bit (of information) at a time One bit encoded for each symbol (carrier wave change)  1 bit per symbol Sending multiple bits simultaneously Multiple bits encoded for each symbol (carrier wave change)  n bits per symbol, n > 1 Need more complicated information coding schemes Copyright 2005 John Wiley & Sons, Inc

Sending Multiple Bits per Symbol
Possible number of symbols must be increased 1 bit of information  2 symbols 2 bits of information  4 symbols 3 bits of information 8  symbols 4 bits of information  16 symbols ……. n bits of information  2n symbols Multiple bits per symbol might be encoded using amplitude, frequency, and phase modulation e.g., PM: phase shifts of 0o, 90o, 180o, and 270o Subject to limitations: As the number of symbols increases, it becomes harder to detect Copyright 2005 John Wiley & Sons, Inc

Combined Modulation Techniques
Combining AM, FM, and PM on the same circuit Examples QAM - Quadrature Amplitude Modulation A widely used family of encoding schemes Combine Amplitude and Phase Modulation A common form: 16-QAM Uses 8 different phase shifts and 2 different amplitude levels 16 possible symbols  4 bits/symbol TCM – Trellis-Coded Modulation An enhancement of QAM Can transmit different number of bits on each symbol (6,7,8 or 10 bits per symbol) Copyright 2005 John Wiley & Sons, Inc

Bit Rate vs. Baud Rate bit: a unit of information baud: a unit of signaling speed Bit rate (or data rate): b Number of bits transmitted per second Baud rate (or symbol rate): s number of symbols transmitted per second General formula: b = s x n where b = Data Rate (bits/second) s = Symbol Rate (symbols/sec.) n = Number of bits per symbol Example: AM n = 1  b = s Example: 16-QAM n = 4  b = 4 x s Copyright 2005 John Wiley & Sons, Inc

Bandwidth of a Voice Circuit
Difference between the highest and lowest frequencies in a band or set if frequencies Human hearing frequency range: 20 Hz to 14 kHz Bandwidth = 14,000 – 20 = 13,980 Hz Voice circuit frequency range: 0 Hz to 4 kHz Designed for most commonly used range of human voice Phone lines transmission capacity is much bigger 1 MHz for lines up to 2 miles from a telephone exchange 300 kHz for lines 2-3 miles away Copyright 2005 John Wiley & Sons, Inc

Data Capacity of a Voice Circuit
Fastest rate at which you can send your data over the circuit (in bits per second) Calculated as the bit rate: b = s x n Depends on modulation (symbol rate) Max. Symbol rate = bandwidth (if no noise) Maximum voice circuit capacity: Using QAM with 4 bits per symbol (n = 4) Max. voice channel carrier wave frequency: 4000 Hz = max. symbol rate (under perfect conditions) Data rate = 4 *  16,000 bps Copyright 2005 John Wiley & Sons, Inc

Modem - Modulator/demodulator
Device that encodes and decodes data by manipulating the carrier wave V-series of modem standards (by ITU-T) V.22 An early standard, now obsolete Used FM, with 2400 symbols/sec  2400 bps bit rate V.34 One of the robust V standards Used TCM (8.4 bits/symbol), with 3,428 symbols/sec  multiple data rates(up to 28.8 kbps) Includes a handshaking sequence that tests the circuit and determines the optimum data rate Copyright 2005 John Wiley & Sons, Inc

Data Compression in Modems
Used to increase the throughput rate of data by encoding redundant data strings Example: Lempel-Ziv encoding Used in V.44 Creates (while transmitting) a dictionary of two-, three-, and four-character combinations in a message Anytime one of these patterns is detected, its index in dictionary is sent (instead of actual data) Average reduction: 6:1 (depends on the text) Provides 6 times more data sent per second Copyright 2005 John Wiley & Sons, Inc

Digital Transmission of Analog Data
Analog voice data sent over digital network using digital transmission Requires a pair of special devices called Codecs - Coder/decoders A device that converts an analog voice signal into digital form Also converts it back to analog data at the receiving end Used by the phone system Copyright 2005 John Wiley & Sons, Inc

Translating from Analog to Digital
Must be translated into a series of bits before transmission of a digital circuit Done by a technique called Pulse Amplitude Modulation (PAM) involving 3 steps: Measuring the signal Encoding the signal as a binary data sample Taking samples of the signal Creates a rough (digitized) approximation of original signal Quantizing error: difference between the original signal and approximated signal Copyright 2005 John Wiley & Sons, Inc

PAM – Measuring Signal Signal (original wave) quantized into 128 pulse amplitudes Requires 8-bit (7 bit plus parity bit) code to encode each pulse amplitude Example: Original wave 8 pulse amplitudes Uses only 8 pulse amplitudes for simplicity Can be depicted by using only a 3-bit code Copyright 2005 John Wiley & Sons, Inc

PAM – Encoding and Sampling
Pulse Amplitudes 000 – PAM Level 1 001 – PAM Level 2 010 – PAM Level 3 011 – PAM Level 4 100 – PAM Level 5 101 – PAM Level 6 110 – PAM Level 7 111 – PAM Level 8 8 pulse amplitudes Digitized signal 8,000 samples per second For digitizing a voice signal, 8,000 samples x 3 bits per sample  24,000 bps transmission rate needed 8,000 samples then transmitted as a serial stream of 0s and 1s Copyright 2005 John Wiley & Sons, Inc

Minimize Quantizing Errors
Increase number of amplitude levels Difference between levels minimized  smoother signal Requires more bits to represent levels  more data to transmit Adequate human voice: 7 bits  128 levels Music: at least 16 bits  65,536 levels Sample more frequently Will reduce the length of each step  smoother signal Adequate Voice signal: twice the highest possible frequency (4Khz x 2 = 8000 samples / second) RealNetworks: 48,000 samples / second Copyright 2005 John Wiley & Sons, Inc

PCM - Pulse Code Modulation
phone switch (DIGITAL) local loop trunk To other switches Analog transmission Central Office (Telco) Digital transmission DS-0: Basic digital communications unit used by phone network Corresponds to 1 digital voice signal convert analog signals to digital data using PCM (similar to PAM) 8000 samples per second and 8 bits per sample (7 bits for sample+ 1 bit for control)  64 Kb/s (DS-0 rate) Copyright 2005 John Wiley & Sons, Inc

ADPCM Adaptive Differential Pulse Code Modulation Encodes the differences between samples The change between 8-bit value of the last time interval and the current one Requires only 4 bits since the change is small  Only 4 bits/sample (instead of 8 bits/sample), Requires 4 x 8000 = 32 Kbps (half of PCM) Makes it possible to for IM to send voice signals as digital signals using modems (which has <56 Kbps) Can also use lower sampling rates, at 8, 16 kbps Lower quality voice signals. Copyright 2005 John Wiley & Sons, Inc

V.90 and V.92 Modems Combines analog and digital transmission Uses a technique based on PCM concept Recognizes PCM’s 8-bit digital symbols (one of 256 possible symbols) 8,000 per second Results in a max of 56 Kbps data rate (1 bit used for control) V.90 Standard Based on V.34+ for Upstream transmissions (PC to Switch) Max. upstream rate is 33.4 Kbps V.92 Standard (most recent) Uses PCM symbol recognition technique for both ways Max. upstream rate is 48 kbps Very sensitive to noise  lower rates Copyright 2005 John Wiley & Sons, Inc

Multiplexing Breaking up a higher speed circuit into several slower (logical) circuits Several devices can use it at the same time Requires two multiplexer: one to combine; one to separate Main advantage: cost Fewer network circuits needed Categories of multiplexing: Frequency division multiplexing (FDM) Time division multiplexing (TDM) Statistical time division multiplexing (STDM) Wavelength division multiplexing (WDM) Copyright 2005 John Wiley & Sons, Inc

Frequency Division Multiplexing
Makes a number of smaller channels from a larger frequency band 3000 Hz available bandwidth Used mostly by CATV FDM FDM Host computer Guardbands needed to separate channels To prevent interference between channels Unused frequency bands ,wasted capacity circuit Four terminals Dividing the circuit “horizontally Copyright 2005 John Wiley & Sons, Inc

Time Division Multiplexing
Dividing the circuit “vertically” Allows multiple channels to be used by allowing the channels to send data by taking turns 4 terminals sharing a circuit, with each terminal sending one character at a time Copyright 2005 John Wiley & Sons, Inc

Comparison of TDM Time on the circuit shared equally Each channel getting a specified time slot, (whether it has any data to send or not ) More efficient than FDM Since TDM doesn’t use guardbands, (entire capacity can be divided up between channels) Copyright 2005 John Wiley & Sons, Inc

Statistical TDM (STDM)
Designed to make use of the idle time slots (In TDM, when terminals are not using the multiplexed circuit, timeslots for those terminals are idle.) Uses non-dedicated time slots Time slots used as needed by the different terminals Complexities of STDM Additional addressing information needed Since source of a data sample is not identified by the time slot it occupies Potential response time delays (when all terminals try to use the multiplexed circuit intensively) Requires memory to store data (in case more data come in than its outgoing circuit capacity can handle) Copyright 2005 John Wiley & Sons, Inc

Wavelength Division Multiplexing
Transmitting data at many different frequencies Lasers or LEDs used to transmit on optical fibers Previously single frequency on single fiber (typical transmission rate being around 622 Mbps) Now multi frequencies on single fiber  n x 622+ Mbps Dense WDM (DWDM) Over a hundred channels per fiber Each transmitting at a rate of 10 Gbps Aggregate data rates in the low terabit range (Tbps) Future versions of DWDM Both per channel data rates and total number of channels continue to rise Possibility of petabit (Pbps) aggregate rates Copyright 2005 John Wiley & Sons, Inc

Inverse Multiplexing (IMUX)
Shares the load by sending data over two or more lines (instead of using a single line) e.g., two T-1 lines used (creating a combined multiplexed capacity of 2 x = Mbps) Bandwidth ON Demand Network Interoperability Group (BONDING) standard Commonly used for videoconferencing applications Six 64 kbps lines can be combined to create an aggregate line of 384 kbps for transmitting video Copyright 2005 John Wiley & Sons, Inc

Digital Subscriber Line (DSL)
Became popular as a way to increase data rates in the local loop. Uses full physical capacity of twisted pair (copper) phone lines (up to 1 MHz) Instead of using the KHz voice channel 1 MHz capacity split into (FDM): a 4 KHz voice channel an upstream channel a downstream channel Requires a pair of DSL modems One at the customer’s site; one at the CO site May be divided further (via TDM) to have one or more logical channels Copyright 2005 John Wiley & Sons, Inc

xDSL Several versions of DSL Depends on how the bandwidth allocated between the upstream and downstream channels a: A for Asynchronous, H for High speed, etc G.Lite - a form of ADSL Provides a 4 Khz voice channel 384 kbps upstream 1.5 Mbps downstream (provided line conditions are optimal). Copyright 2005 John Wiley & Sons, Inc

Digital is better Easier, more manageable , and less costly to integrate voice, data, and video Organizational impact Convergence of physical layer causing convergence of phone and data departments Impact on telecom industry Disappearance of the separation between manufacturers of telephone equipment and manufacturers of data equipment Copyright 2005 John Wiley & Sons, Inc

Outline Media Access Control Controlled Access, Contention, Relative Performance Error Control Sources of Errors, Error Prevention, Error Detection, Error Correction via Retransmission, Forward Error Correction Data Link Protocols Asynchronous Transmission, Asynchronous File Transfer Protocols, Synchronous Transmission Transmission Efficiency Copyright 2005 John Wiley & Sons, Inc

Data Link Layer - Introduction
Responsible for moving messages from one device to another Controls the way messages are sent on media Organizes physical layer bit streams into coherent messages for the network layer Major functions of a data link layer protocol Media Access Control Controlling when computers transmit Error Control Detecting and correcting transmission errors Message Delineation Identifying the beginning and end of a message Network Layer Data Link Layer Physical Layer Copyright 2005 John Wiley & Sons, Inc

Media Access Control (MAC)
Controlling when and what computers transmit Important when more than one computer wants to send data (at the same time over the same circuit); e.g., Point-to-point half duplex links computers to take turns Multipoint configurations Ensure that no two computers attempt to transmit data at the same time Main approaches Controlled access Contention based access Copyright 2005 John Wiley & Sons, Inc

Controlled Access Controlling access to shared resources Acts like a stop light Commonly used by mainframes (or its front end processor) Determines which circuits have access to mainframe at a given time Also used by some LAN protocols Token ring, FDDI Major controlled access methods X-ON/X-OFF and Polling Copyright 2005 John Wiley & Sons, Inc

X-ON / X-OFF An older controlled access protocol A B Request to Transmit X-ON not busy data transmitting data Pausing (periodically done) X-OFF busy X-ON not busy transmitting data data Still used between a computer and a printer Still used on some half duplex circuits, but it is fading Copyright 2005 John Wiley & Sons, Inc

Polling Process of transmitting to a client only if asked and/or permitted Client stores the info to be transmitted Server (periodically) polls the client if it has data to send Client, if it has any, sends the data If no data to send, client responds negatively, and server asks the next client Types of polling Roll call polling Hub polling (also called token passing) Copyright 2005 John Wiley & Sons, Inc

Roll Call Polling Check each client (consecutively and periodically) to see if it wants to transmit : A, B, C, D, E, A, B, … Clients D C E B Server A Clients can also be prioritized so that they are polled more frequently: A, B, A, C, A, D, A, E, A, B, .. Involves waiting: Poll and wait for a response Needs a timer to prevent lock-up (by client not answering) Copyright 2005 John Wiley & Sons, Inc

Hub Polling (Token Passing)
One computer starts the poll: sends message (if if any) then passes the token on to the next computer E B C D A token Continues in sequence until the token reaches the first computer, which starts the polling cycle all over again Copyright 2005 John Wiley & Sons, Inc

Contention Transmit whenever the circuit is free Collisions Occurs when more than one computer transmitting at the same time Need to determine which computer is allowed to transmit first after the collision Used commonly in Ethernet LANs Copyright 2005 John Wiley & Sons, Inc

Relative Performance Depends on network conditions
When volume is high, performance deteriorates (too many collisions) Work better for networks with high traffic volumes Cross-over point: About 20 computers Network more efficiently used Work better for smaller networks with low usage Copyright 2005 John Wiley & Sons, Inc

Error Control Handling of network errors caused by problems in transmission Network errors e.g., changing a bit value during transmission Controlled by network hardware and software Human errors: e.g., mistake in typing a number Controlled by application programs Categories of Network Errors Corrupted (data changed) Lost data Copyright 2005 John Wiley & Sons, Inc

Error Control (Cont.) Error Rate 1 bit error in n bits transmitted, e.g., 1 in 500,000 Burst error Many bits are corrupted at the same time Errors not uniformly distributed e.g., 100 in 50,000,000  1 in 500,000 Major functions Preventing errors Detecting errors Correcting errors Copyright 2005 John Wiley & Sons, Inc

Sources of Errors Line noise and distortion – major cause More likely on electrical media Undesirable electrical signal Introduced by equipment and natural disturbances Degrades performance of a circuit Manifestation Extra bits “flipped” bits Missing bits Copyright 2005 John Wiley & Sons, Inc

Sources of Errors and Prevention
Source of Error What causes it How to prevent it Line Outages Faulty equipment, Storms, Accidents (circuit fails) White Noise (hiss) (Gaussian Noise) Movement of electrons (thermal energy) Increase signal strength (increase SNR) Impulse Noise (Spikes) Sudden increases in electricity (e.g., lightning, power surges) Shield or move the wires Cross-talk Multiplexer guard bands are too small or wires too close together Increase the guard bands, or move or shield the wires Echo Poor connections (causing signal to be reflected back to the source) Fix the connections, or tune equipment Attenuation Gradual decrease in signal over distance (weakening of a signal) Use repeaters or amplifiers Intermodulation Noise Signals from several circuits combine Move or shield the wires Jitter Analog signals change (small changes in amp., freq., and phase) Tune equipment Harmonic Distortion Amplifier changes phase (does not correctly amplify its input signal) More important mostly on analog Copyright 2005 John Wiley & Sons, Inc

Error Detection Sender calculates an Error Detection Value (EDV) and transmits it along with data Receiver recalculates EDV and checks it against the received EDV Mathematical calculations Mathematical calculations ? = Data to be transmitted EDV If the same  No errors in transmission If different  Error(s) in transmission Larger the size, better error detection (but lower efficiency) Copyright 2005 John Wiley & Sons, Inc

Error Detection Techniques
Parity checks Longitudinal Redundancy Checking (LRC) Polynomial checking Checksum Cyclic Redundancy Check (CRC) Copyright 2005 John Wiley & Sons, Inc

Parity Checking One of the oldest and simplest A single bit added to each character Even parity: number of 1’s remains even Odd parity: number of 1’s remains odd Receiving end recalculates parity bit If one bit has been transmitted in error the received parity bit will differ from the recalculated one Simple, but doesn’t catch all errors If two (or an even number of) bits have been transmitted in error at the same time, the parity check appears to be correct Detects about 50% of errors Copyright 2005 John Wiley & Sons, Inc

Examples of Using Parity
To be sent: Letter V in 7-bit ASCII: sender receiver EVEN parity parity number of all transmitted 1’s remains EVEN sender receiver ODD parity parity number of all transmitted 1’s remains ODD Copyright 2005 John Wiley & Sons, Inc

LRC - Longitudinal Redundancy Checking
Adds an additional character (instead of a bit) Block Check Character (BCC) to each block of data Determined like parity but, but counting longitudinally through the message (as well as vertically) Calculations are based on the 1st bit, 2nd bit, etc. (of all characters) in the block 1st bit of BCC  number of 1’s in the 1st bit of characters 2nd bit of BCC number of 1’s in the 2ndt bit of characters Major improvement over parity checking 98% error detection rate for burst errors ( > 10 bits) Less capable of detecting single bit errors Copyright 2005 John Wiley & Sons, Inc

Using LRC for Error Detection
Example: Send the message “DATA” using ODD parity and LRC Letter D A T ASCII Parity bit 1 BCC Note that the BCC’s parity bit is also determined by parity Copyright 2005 John Wiley & Sons, Inc

Polynomial Checking Adds 1 or more characters to the end of message (based on a mathematical algorithm) Two types: Checksum and CRC Checksum Calculated by adding decimal values of each character in the message, Dividing the total by 255. and Saving the remainder (1 byte value) and using it as the checksum 95% effective Cyclic Redundancy Check (CRC) Computed by calculating the remainder to a division problem: Copyright 2005 John Wiley & Sons, Inc

Cyclic Redundancy Check (CRC)
Example: P = 58 G = 8 Q = 7 R = 2 P / G = Q + R / G Quotient (whole number) Message (treated as one long binary number) Remainder: added to the message as EDV) could be 8 bits, 16 bits, 24 bits, or 32 bits long A fixed number (determines the length of the R) Most powerful and most common Detects 100% of errors (if number of errors <= size of R) Otherwise: CRC-16 (99.998%) and CRC-32 ( %) Copyright 2005 John Wiley & Sons, Inc

Error Correction Once detected, the error must be corrected Error correction techniques Retransmission (a.k.a, Backward error correction) Simplest, most effective, least expensive, most commonly used Corrected by retransmission of the data Receiver, when detecting an error, asks the sender to retransmit the message Often called Automatic Repeat Request (ARQ) Forward Error Correction Receiving device can correct incoming messages itself Copyright 2005 John Wiley & Sons, Inc

Automatic Repeat Request (ARQ)
Process of requesting that a data transmission be resent Main ARQ protocols Stop and Wait ARQ (A half duplex technique) Sender sends a message and waits for acknowledgment, then sends the next message Receiver receives the message and sends an acknowledgement, then waits for the next message Continuous ARQ (A full duplex technique) Sender continues sending packets without waiting for the receiver to acknowledge Receiver continues receiving messages without acknowledging them right away Copyright 2005 John Wiley & Sons, Inc

Stop and Wait ARQ Sender Receiver Sends the packet, then waits to hear from receiver. Sends acknowledgement Sends the next packet Sends negative acknowledgement Resends the packet again Copyright 2005 John Wiley & Sons, Inc

Continuous ARQ Sender sends packets continuously without waiting for receiver to acknowledge Notice that acknowledgments now identify the packet being acknowledged. Receiver sends back a NAK for a specific packet to be resent. Copyright 2005 John Wiley & Sons, Inc

Flow Control with ARQ Ensuring that sender is not transmitting too quickly for the receiver Stop-and-wait ARQ Receiver sends an ACK or NAK when it is ready (to receive more packets) Continuous ARQ: Both sides agree on the size of the sliding window Number of messages that can be handled by the receiver without causing significant delays) Copyright 2005 John Wiley & Sons, Inc

Flow Control Example window size =4 receiver sender ACK 0... (slide window) ...4 ACK 4... (slide window) … set window size to 2 ACK 7.. (slide window) ..9 (timeout) ...9 8 Copyright 2005 John Wiley & Sons, Inc

Forward Error Correction (FEC)
Receiving device can correct incoming messages itself (without retransmission) Requires extra corrective information Sent along with the data Allows data to be checked and corrected by the receiver Amount of extra information: usually % of the data Useful for satellite transmission One way transmissions (retransmission not possible) Transmission times are very long (retransmission will take a long time) Insignificant cost of FEC (compare to total cost of eq.) Copyright 2005 John Wiley & Sons, Inc

Hamming Code – An FEC Example
Each data bit figures into three EVEN parity bit calculations Only works for one bit errors If any one bit (parity or data) changes  change in data bit can be detected and corrected Copyright 2005 John Wiley & Sons, Inc

Data Link Protocols Classification Asynchronous transmission Synchronous transmission Differ by Message delineation Frame length Frame field structure frame k-1 frame k frame k+1 Copyright 2005 John Wiley & Sons, Inc

Asynchronous Transmission
Sometimes called start-stop transmission Used by the receiver for separating characters and for synch. Each character is sent independently Sent between transmissions (a series of stop bits) Used on point-to-point full duplex circuits (used by Telnet when you connect to Unix/Linux computers) Copyright 2005 John Wiley & Sons, Inc

Asynchronous File Transfer
Used on Point-to-point asynchronous circuits Typically over phone lines via modem Computer to computer for transfer of data files Characteristics of file transfer protocols Designed to transmit error-free data Group data into blocks to be transmitted (rather sending character by character) Popular File transfer Protocols Xmodem, Zmodem, and Kermit Copyright 2005 John Wiley & Sons, Inc

File Transfer Protocols
Xmodem One of the oldest async file transfer protocol Uses stop-and-wait ARQ. Start of Header SOH Packet # Packet # compl. (128 bytes) Checksum Xmodem-CRC: uses 1 byte CRC (instead of checksum) Xmodem-1K: Xmodem-CRC byte long message field Zmodem Uses CRC-32 with continuous ARQ Dynamic adjustment of packet size (based on circuit) Kermit Very flexible, powerful and popular Typically uses CRC-24 and 1K size, but adjustable Copyright 2005 John Wiley & Sons, Inc

Synchronous Transmission
Data sent in a large block Called a frame or packet Typically about a thousand characters (bytes) long Includes addressing information Especially useful in multipoint circuits Includes a series of synchronization (SYN) characters Used to help the receiver recognize incoming data Synchronous transmission protocols categories Bit-oriented protocols: SDLC, HDLC Byte-count protocols: Ethernet Byte-oriented protocols: PPP Copyright 2005 John Wiley & Sons, Inc

SDLC – Synchronous Data Link Control
Bit-oriented protocol developed by IBM Uses a controlled media access protocol Beginning ( ) Ending ( ) data CRC-32 Destination Address (8 or 16 bits) Identifies frame type; Information (for transferring of user data) Supervisory (for error and flow control) Copyright 2005 John Wiley & Sons, Inc

Transparency Problem of SDLC
Problem: Transparency User data may contain the same bit pattern as the flags ( ) Receiver may interpret it as the end of the frame and ignores the rest Solution: Bit stuffing (aka, zero insertion) Sender inserts 0 anytime it detects (five 1’s) If receiver sees five 1's, checks next bit(s) if 0, remove it (stuffed bit) if 10, end of frame marker ( ) if 11, error (7 1's cannot be in data) Works but increases complexity Copyright 2005 John Wiley & Sons, Inc

HDLC – High-Level Data Link Control
Formal standard developed by ISO Same as SDLC, except Longer address and control fields Larger sliding window size And more Basis for many other Data Link Layer protocols LAP-B (Link Accedes Protocol – Balanced) Used by X.25 technology LAP-D (Link Accedes Protocol – Balanced) Used by ISDN technology LAP- F (Used by Frame Relay technology) Copyright 2005 John Wiley & Sons, Inc

Ethernet (IEEE 802.3) Most widely used LAN protocol, developed jointly by Digital, Intel, and Xerox, now an IEEE standard Uses contention based media access control Byte-count data link layer protocol No transparency problem uses a field containing the number of bytes (not flags) to delineate frames Error correction: optional Copyright 2005 John Wiley & Sons, Inc

Ethernet (IEEE 802.3) Frame Used by Virtual LANs; (if no vLAN, the field is omitted If used, first 2 bytes is set to: 24,832 (8100H) Used to hold sequence number, ACK/NAK, etc., (1 or 2 bytes) 00 01 10 11 Data ( bytes) (number of bytes in the message field) Repeating pattern of 1’s and 0’s ( ) Used to exchange control info (e.g., type of network layer protocol used) Copyright 2005 John Wiley & Sons, Inc

Point-to-Point Protocol (PPP)
Byte-oriented protocol developed in early 90s Commonly used on dial-up lines from home PCs Designed mainly for point-to-point phone line (can be used for multipoint lines as well) (up to 1500 bytes) Specifies the network layer protocol used (e.g, IP, IPX) Copyright 2005 John Wiley & Sons, Inc

Data Link Protocol Summary
Data Link Protocol Summary Protocol Size Error Detection Retransmission Media Access Asynchronous Xmission 1 Parity Continuous ARQ Full Duplex File Transfer Protocols XMODEM 132 8-bit Checksum Stop-and-wait ARQ Controlled Access XMODEM-CRC 8-bit CRC XMODEM-1K 1028 ZMODEM * 32-bit CRC KERMIT 24-bit CRC Synchronous Protocols SDLC 16-bit CRC HDLC Token Ring Stop-and wait ARQ Ethernet Contention SLIP None PPP * Varies depending on message length. Copyright 2005 John Wiley & Sons, Inc

Transmission Efficiency
An objective of the network: Move as many bits as possible with min errors  higher efficiency and lower cost Factors affecting network efficiency: Characteristics of circuit (error rate, speed) Speed of equipment, Error control techniques Protocol used Information bits (carrying user information) Overhead bits ( used for error checking, frame delimiting, etc.) Total number of info bits to be transmitted Total number of bits transmitted = Copyright 2005 John Wiley & Sons, Inc

Transmission Efficiency of Protocols
Async Transmission: 7-bit ASCII (info bits), 1 parity bit, 1 stop bit, 1 start bit Transmission Efficiency = 7 / 10  70% e.g., V.92 modem with 56 Kbps  39.2 Kbps effective rate SDLC Transmission Assume 100 info characters (800 bits), 2 flags (16 bits) Address (8 bits), Control (8 bits), CRC (32 bits) Transmission Efficiency = 800 / 64  92.6% e.g., V.92 modem with 56 Kbps  51.9 Kbps effective rate Bigger the message length, better the efficiency However, large packets likely to have more errors (more likely to require retransmission)  wasted capacity Copyright 2005 John Wiley & Sons, Inc

Throughput A more accurate definition of efficiency Total number of information bits received per second; takes into account: Overhead bits (as in transmission efficiency) Need to retransmit packets containing errors Complex to calculate; depends on Transmission efficency Error rate Number of retransmission Transmission Rate of Information Bits (TRIB) Used as a measurement of throughput Copyright 2005 John Wiley & Sons, Inc

Optimum Packet Size Trade-off between packet size and throughput Acceptable range (more costly in terms of circuit capacity to retransmit if there is an error) (less likely to contain errors) Copyright 2005 John Wiley & Sons, Inc

TRIB K (M – C) (1 – P) TRIB = (M / R) + T
= Number of info bits accepted / total time required to get the bits (number of info bits) (Prob. Of successful xmission) time it takes to transmit these bits + propagation delay Ex: K=7 bits/character M = 400 char/block R= 4.8 Kb/s C = 10 char/block P = 1% T = 25 ms Average number of non-info characters per block Probability that a block will require retransmission Info bits per character K (M – C) (1 – P) (M / R) + T TRIB = 7(400-10)(1-0.01) (400/600)+0.025) = Kb/s TRIB = Packet length in characters Time between blocks (in seconds) (propagation time + turnaround time) (a.k.a., reclocking time) Data xmission rate in char per second Copyright 2005 John Wiley & Sons, Inc

Provide a few, widely used data link layer protocols for all networks Minimize costly customization Minimize costly translation among many protocols Less training, simpler network management Bigger pool of available experts Less expensive, off-the-shelf equipment Copyright 2005 John Wiley & Sons, Inc

Network and Transport Layers
Chapter 5 Network and Transport Layers Copyright 2005 John Wiley & Sons, Inc

Outline Transport & Network Layer Protocols TCP/IP, IPX/SPX, X.25, SNA Transport Layer Functions Interacting with Application Layer Packetizing End-to-end delivery of application layer messages Network Layer Functions Addressing Routing TCP/IP Examples Copyright 2005 John Wiley & Sons, Inc

Introduction Transport and Network layers Responsible for moving messages from end-to-end in a network Closely tied together TCP/IP: most commonly used protocol Used in Internet Compatible with a variety of Application Layer protocols as well as with many Data Link Layer protocols Application Layer Transport Layer Network Layer Data Link Layer Copyright 2005 John Wiley & Sons, Inc

Introduction - Transport layer
Responsible for end-to-end delivery of messages Sets up virtual circuits (when needed) Responsible for segmentation and reassembly Breaking the message into several smaller pieces at the sending end Reconstructing the original message into a single whole at the receiving end Interacts with Application Layer Application Layer Transport Layer Network Layer Copyright 2005 John Wiley & Sons, Inc

Introduction – Network Layer
Responsible for addressing and routing of messages Selects the best path from computer to computer until the message reaches destination Performs encapsulation on sending end Adds network layer header to message segments Performs decapsulation on receiving end Removes the network layer header at receiving end and passes them up to the transport layer Transport Layer Network Layer Data Link Layer Copyright 2005 John Wiley & Sons, Inc

TCP/IP’s 5-Layer Network Model

Transport/Network Layer Protocols
TCP/IP (Transmission Control Protocol / Internet Protocol) Most common, used by all Internet equipment IPX/SPX Similar to TCP/IP Mainly used by Novell networks (Novell has since replaced it with TCP/IP) X.25 Used mainly in Europe SNA (System Network Architecture) IBM’s protocol suite Copyright 2005 John Wiley & Sons, Inc

TCP/IP Developed in ‘74 by V. Cerf and B. Kahn As part of Arpanet (U.S. Department of Defense) Most common protocol suite Used by the Internet. Almost 70% of all backbone, metropolitan, and wide area networks use TCP/IP Most common protocol on LANs (surpassed IPX/SPX in ‘98) Reasonably efficient and error free transmission Performs error checking Transmits large files with end-to-end delivery assurance Compatible with a variety of data link layer protocols Copyright 2005 John Wiley & Sons, Inc

Transmission Control Protocol
Links the application layer to the network layer Performs packetization and reassembly Breaking up a large message into smaller packets Numbering the packets and Reassembling them at the destination end Ensures reliable delivery of packets used in message reassembly TCP Header: 192 bits (24 bytes) Copyright 2005 John Wiley & Sons, Inc

Internet Protocol (IP)
Responsible for addressing and routing of packets Two versions in current in use IPv4: a 192 bit (24 byte) header, uses 32 bit addresses. IPv6: Mainly developed to increase IP address space due to the huge growth in Internet usage (128 bit addresses) Both versions have a variable length data field Max size depends on the data link layer protocol. e.g., Ethernet’s max message size is 1,492 bytes, so max size of TCP message field: 1492 – 24 – 24 = 1444 bytes TCP header IPv4 header Copyright 2005 John Wiley & Sons, Inc

X.25 Developed by ITU-T for use in WANs Widely used especially in Europe Seldom used in North America Transport layer protocols for X.25 X.3 (performs packetization for ASCII terminals) TP (ISO defined), TCP Network Layer protocol for X.25 Packet Layer Protocol (PLP) for routing and addressing Data Link Layer protocol for X.25 LAP-B (Link Access Protocol-Balanced) Recommended packet size: 128 bytes But can support packet sizes up to 1024 bytes. Copyright 2005 John Wiley & Sons, Inc

SNA - Systems Network Architecture
Developed by IBM Used on IBM and IBM-compatible mainframes Based on non-standard proprietary protocols Difficult to integrate with non-SNA networks Requires special equipment, gateways (to route messages between SNA and non-SNA networks) Likely disappear over time IBM now offers TCP/IP on its networks Copyright 2005 John Wiley & Sons, Inc

Transport Layer Functions
Linking to Application Layer Packetization and Reassembly Establishing connection (virtual) Connection Oriented Connectionless Quality of Service (QoS) Copyright 2005 John Wiley & Sons, Inc

Linking to Application Layer
TCP may serve several Application Layer protocols at the same time Problem: Which application layer program to send a message to? Solution: Port numbers located in TCP header fields; 2-byte each (source, destination) Standard port numbers Usual practice Nonstandard port numbers Possible, but requires configuration of TCP TCP HTTP FTP SMTP … 80 21 25 Copyright 2005 John Wiley & Sons, Inc

Application Layer Services

Packetization and Reassembly
Application layer sees message as a single block of data FTP FTP TCP TCP IP IP sender receiver Breaks a large message into smaller pieces (packetization) Puts them back together at the destination (reassembly) What size packet to use? Done through negotiations Delivers incoming packets as they arrive (e.g., Web pages) or to wait until entire message arrives (e.g., ) Copyright 2005 John Wiley & Sons, Inc

Setting up Virtual Connections
B SYN Requests a virtual circuit (TCP connection) and negotiates packet size with B SYN Data 1 Data 2 Sends data packets one by one (in order) using continuous ARQ (sliding window) ACK 2 Data 3 Data 4 FIN Closes virtual circuit not busy Copyright 2005 John Wiley & Sons, Inc

Routing Implied by Transport Layer
Connection Oriented (provided by TCP) Setting up a virtual circuit (a TCP connection) TCP asks IP to route all packets in a message by using the same path (from source to destination) Packet deliveries are acknowledged Used by HTTP, SMTP, FTP Connectionless Routing (provided by UDP Sending packets individually without a virtual circuit Each packet is sent independently of one another (routed separately and can follow different routes and arrive at different times) QoS Routing (provided by RTP) A special kind connection oriented routing with priorities Copyright 2005 John Wiley & Sons, Inc

UDP - User Datagram Protocol
Protocol used for connectionless routing in TCP/IP suite (no acks, no flow control) Uses only a small packet header Only 8 bytes containing only 4 fields: Source port Destination port Message length Header checksum Commonly used for control messages that are usually small, such as DNS, DHCP, RIP and SNMP. Copyright 2005 John Wiley & Sons, Inc

QoS - Quality of Service
QoS parameters Availability, Reliability, Timeliness Timeliness - timely delivery of packets Packets be delivered within a certain period of time (to produce a smooth, continuous output Required by some applications, especially real time applications (e.g., voice and video frames) ( doesn’t require this) QoS routing Defines classes of service, each with a different priority: Real-time applications - highest A graphical file for a Web page - a lower priority - lowest (can wait a long time before delivery) Copyright 2005 John Wiley & Sons, Inc

Protocols Supporting QoS
Asynchronous Transfer Mode (ATM) A high-speed data link layer protocol TCP/IP protocol suite Resource Reservation Protocol (RSVP) Sets up virtual circuits for general purpose real-time applications Real-Time Streaming Protocol (RTSP) Sets up virtual circuits for audio-video applications Real-Time Transport Protocol (RTP) Used after a virtual connection setup by RSVP or RTSP Adds a sequence number and a timestamp for helping applications to synchronize delivery Uses UDP (because of its small header) as transport RSVP RTSP RTP UDP IP Copyright 2005 John Wiley & Sons, Inc

Network Layer Functions
Addressing Each equipment on the path between source and destination must have an address Internet Addresses Assignment of addresses Translation between network layer addresses and other addresses (address resolution) Routing Process of deciding what path a packet must take to reach destination Routing protocols Copyright 2005 John Wiley & Sons, Inc

Types of Addresses Address Type Example Example Address Analogy Application Layer URL Name Network Layer Street # IP address (4 bytes) Data Link Layer MAC address 00-0C-00-F5-03-5A (6 bytes) Apt # These addresses must be translated from one type to another (for a message to travel from sender to receiver). This translation process is called address resolution. Try “ping”ing a URL; translation (corresponding IP address) will be given by the answer. Copyright 2005 John Wiley & Sons, Inc

Assignment of Addresses
Application Layer address (URL) For servers only (clients don’t need it) Assigned by network managers and placed in configuration files. Some servers may have several application layer addresses Network Layer Address (IP address) Assigned by network managers, or by programs such as DHCP, and placed in configuration files Every network on the Internet is assigned a range of possible IP addresses for use on its network Data Link Layer Address (MAC address) Unique hardware addresses placed on network interface cards by their manufacturers ( based on a standardized scheme) Servers have permanent addresses, clients usually do not Copyright 2005 John Wiley & Sons, Inc

Internet Addresses Managed by ICANN Internet Corporation for Assigned Names and Numbers Manages the assignment of both IP and application layer name space (domain names) Both assigned at the same time and in groups Manages some domains directly (e.g., .com, .org, .net) and Authorizes private companies to become domain name registrars as well Example: Indiana University URLs that end in .indiana.edu and iu.edu IP addresses in the x.x range (where x is any number between 0 and 255) Copyright 2005 John Wiley & Sons, Inc

IPv4 Addresses 4 byte (32 bit) addresses Strings of 32 binary bits Dotted decimal notation Used to make IP addresses easier to understand for human readers Breaks the address into four bytes and writes the digital equivalent for each byte Example: Copyright 2005 John Wiley & Sons, Inc

Classfull Adressing 7 bits 24 bits Class A Net ID Host ID 2^31 = 2 Billion addresses 0 -127 14 bits 16 bits Class B 1 0 Net ID Host ID 2^30 = 1 Billion addresses 21 bits 8 bits Class C 1 1 0 Net ID Host ID 2^29 = 536 Million addresses Class D 2^28 = 268 Million addresses Class E 2^28 = 268 Million addresses Copyright 2005 John Wiley & Sons, Inc

IPv6 Addressing Need IPv4 uses 4 byte addresses: Total of one billion possible addresses IP addresses often assigned in (large) groups Giving out many numbers at a time  IPv4 address space has been used up quickly e.g., Indiana University: uses a Class A IP address space (65,000 addresses; many more than needed) IPv6 uses 16 byte addresses: 3.2 x 1038 addresses, a very large number Little chance this address space will ever be used up Copyright 2005 John Wiley & Sons, Inc

Subnets Group of computers on the same LAN with IP numbers with the same prefix Assigned addresses that are 8 bits in length For example: Subnet x Computers in Business (x is between 0 & 255) Subnet x Computers in CS department Assigned addresses could be more or less than eight bits in length For example: If 7 bits used for a subnet Subnet 1: Subnet 2: Copyright 2005 John Wiley & Sons, Inc

Subnet Masks Used to make it easier to separate the subnet part of the address from the host part. Example Subnet: x Subnet mask: or in binary Subnets: , Subnet mask or, in binary: Copyright 2005 John Wiley & Sons, Inc

Dynamic Addressing Giving addresses to clients (automatically) only when they are logged in to a network Eliminates permanent addresses to clients When the computer is moved to another location, its new IP address is assigned automatically Makes efficient use of IP address space Example: A small ISP with several thousands subscribers Might only need to assign 500 IP addresses to clients at any one time Uses a server to supply IP addresses to computers whenever the computers connect to network Copyright 2005 John Wiley & Sons, Inc

Programs for Dynamic Addressing
Bootstrap Protocol (bootp) Dynamic Host Control Protocol (DHCP) Different approaches, but same basic operations: A program residing in a client establishes connection to bootp or DHCP server A client broadcasts a message requesting an IP address (when it is turned on and connected) Server (maintaining IP address pool) responds with a message containing IP address (and its subnet mask) IP addresses can also be assigned with a time limit (leased IP addresses) When expires, client must send a new request Copyright 2005 John Wiley & Sons, Inc

Address Resolution Server Name Resolution Translating destination host’s domain name to its corresponding IP address e.g.,  ) Uses one or more Domain Name Service (DNS) servers to resolve the address Data Link Layer Address Resolution Identifying the MAC address of the next node (that packet must be forwarded t) Uses Address Resolution Protocol (ARP) Copyright 2005 John Wiley & Sons, Inc

DNS - Domain Name Service
Used to determine IP address for a given URL Provided through a group of name servers Databases containing directories of domain names and their corresponding IP addresses Large organizations maintain their own name servers smaller organizations rely on name servers provided by their ISPs When a domain name is registered, IP address of the DNS server must be provided to registrar for all URLs in this domain Example: Domain name: indiana.edu URLs: abc.indiana.edu Copyright 2005 John Wiley & Sons, Inc

How DNS Works Desired URL in client’s address table: Use the corresponding IP address Each client maintains a server address table containing URLs used and corresponding IP addresses Desired URL not in client’s address table: Use DNS to resolve the address Sends a DNS request packet to its local DNS server URL in Local DNS server Responds by sending a DNS response packet back to the client Copyright 2005 John Wiley & Sons, Inc

How DNS Works (Cont.) URL NOT in Local DNS server Sends DNS request packet to the next highest name server in the DNS hierarchy Usually the DNS server at the top level domain (such as the DNS server for all .edu domains) URL NOT in the name server Sends DNS request packet ahead to name server at the next lower level of the DNS hierarchy Copyright 2005 John Wiley & Sons, Inc

Client computer DNS Server DNS Request LAN Internet Root DNS Server for .EDU domain University of Toronto Indiana University DNS Response Asks for a web page on Indiana University’s server How DNS Works Copyright 2005 John Wiley & Sons, Inc

MAC Address Resolution
Problem: Unknown MAC address of the next node (whose IP address known) Solution: Uses Address Resolution Protocol (ARP) Operation Broadcast an ARP message to all nodes on a LAN asking which node has a certain IP address Host with that IP address then responds by sending back its MAC address Store this MAC address in its address table Send the message to the destination node Example of a MAC address: 00-0C-00-F5-03-5A Copyright 2005 John Wiley & Sons, Inc

Routing Process of identifying what path to have a packet take through a network from sender to receiver Routing Tables Used to make routing decisions Shows which path to send packets on to reach a given destination Kept by computers making routing decisions Routers Special purpose devices used to handle routing decisions on the Internet Maintain their own routing tables Dest. B C D E F G Next Copyright 2005 John Wiley & Sons, Inc

Possible paths from A to G: Copyright 2005 John Wiley & Sons, Inc
Routing Example Possible paths from A to G: ABCG ABEFCG ADEFCG ADEBCG B A Routing Table for A Dest. B C D E F G Next Each node has its own routing table Copyright 2005 John Wiley & Sons, Inc

Types of Routing Centralized routing Decisions made by one central computer Used on small, mainframe-based networks Decentralized routing Decisions made by each node independently of one another Information need to be exchanged to prepare routing tables Used by Internet Copyright 2005 John Wiley & Sons, Inc

Types of Decentralized Routing
Static routing: Uses fixed routing tables developed by network managers Each node has its own routing table Changes when computers added or removed Used on relatively simple networks (with few routing options that rarely change) Dynamic routing (aka. Adaptive routing): Uses routing tables (at each node) that are updated dynamically Based on routing condition information exchanged between routing devices Copyright 2005 John Wiley & Sons, Inc

Dynamic Routing Algorithms
Distance Vector Uses the least number of hops to decide how to route a packet Used by Routing Information Protocol (RIP) Link State Uses a variety of information types to decide how to route a packet (more sophisticated) e.g., number of hops, congestion, speed of circuit Links state info exchanged periodically by each node to keep every node in the network up to date Provides more reliable, up to date paths to destinations Used by Open Shortest Path First (OSPF) C B G D F E Ex: From A to G  ABCG Copyright 2005 John Wiley & Sons, Inc

Routing Protocols Used to exchange info among nodes for building and maintaining routing tables Autonomous System (AS) A network operated by an organization (e.g., Indiana U.) Protocols classified based on autonomous systems Types of Routing Protocols Interior routing protocols (RIP, OSPF, EIGRP, ICMP) Operate within a network (autonomous system) Provide detailed info about each node and paths Exterior routing protocols (BGP) Operate between networks (autonomous systems) Copyright 2005 John Wiley & Sons, Inc

Routing Information Protocol (RIP)
A dynamic distance vector interior routing protocol Once popular on Internet; now used on simple networks Operations: Manager builds a routing table by suing RIP Routing tables broadcast periodically (every minute or so) by all nodes When a new node added, RIP counts number of hops between computers and updates routing tables Copyright 2005 John Wiley & Sons, Inc

Open Shortest Path First (OSPF)
A dynamic link state interior routing protocol Became more popular on Internet More reliable paths Incorporates traffic and error rate measures Less burdensome to the network Only the updates sent (not entire routing tables) and only to other routers (no broadcasting) Copyright 2005 John Wiley & Sons, Inc

Other Interior Routing Protocols
Enhanced Interior Gateway Routing Protocol (EIGRP) A dynamic link state protocol (developed by Cisco) Records transmission capacity, delay time, reliability and load for all paths Keeps the routing tables for its neighbors and uses this information in its routing decisions as well Internet Control Message Protocol (ICMP) Simplest and most basic An error reporting protocol (report routing errors to message senders) Limited ability to update routing tables Copyright 2005 John Wiley & Sons, Inc

Exterior Routing Protocols
Border Gateway Protocol (BGP) Used to exchange routing info between autonomous systems Based on a dynamic distance vector algorithm Far more complex than interior routing protocols Provide routing info only on selected routes (e.g., preferred or best route) Privacy concern Too many routes; can’t maintain tables of every single rout Copyright 2005 John Wiley & Sons, Inc

Internet Routing using BGP, OSPF and RIP
Router 1 Router 4 Router 3 OSPF Designated Router Border Router Router 2 Autonomous System A (using OSPF) Border Router Autonomous System B (using RIP) Autonomous System C BGP Autonomous System E Autonomous System D Autonomous System F Router 5 Internet Routing using BGP, OSPF and RIP Copyright 2005 John Wiley & Sons, Inc

Multicasting Casting Unicast message: one computer  another computer Broadcast message: one computer  all computers in the network Multicast message: one computer  a group of computers (e.g., videoconference) Internet Group Management Protocol (IGMP) Provides a way for a computer to report its multicast group membership to adjacent routers A special IP address assigned to identify the group Routing node sets MAC address to a matching MAC address When multicast session ends, IGMP sends a message to the organizing computer( or router) to remove multicast group Copyright 2005 John Wiley & Sons, Inc

Sending Messages using TCP/IP
Required Network layer addressing information Computer’s own IP address Its subnet mask To determine what addresses are part of its subnet Local DNS server’s IP address To translate URLs into IP addresses IP address of the router (gateway) on its subnet To route messages going outside of its subnet Obtained from a configuration file or provided by a DHCP server Servers also need to know their own application layer addresses (domain names) Copyright 2005 John Wiley & Sons, Inc

TCP/IP Configuration Information

TCP/IP Network Example

Case 1a: Known Address, Same Subnet
A Client ( ) requests a Web page from a server (www1.anyorg.com) Client knows the server’s IP and Ethernet addresses Operations (performed by the client) Prepare HTTP packet and send it to TCP Place HTTP packet into a TCP packet and sent it to IP Place TCP packet into an IP packet, add destination IP address, Use its subnet mask to see that the destination is on the same subnet as itself Add server’s Ethernet address into its destination address field, and send the frame to the Web server Copyright 2005 John Wiley & Sons, Inc

Case 1b: HTTP response to client
Operations (performed by the server) Receive Ethernet frame, perform error checking and send back an ACK Process incoming frame successively up the layers (data link, network, transport and application) until the HTTP request emerges Process HTTP request and sends back an HTTP response (with requested Web page) Process outgoing HTTP response successively down the layers until an Ethernet frame is created Send Ethernet frame to the client Operations (performed by the client) Receive Ethernet frame and process it successively up the layers until the HTTP response emerges at browser Copyright 2005 John Wiley & Sons, Inc

Case 2: Known Address, Different Subnet
Similar to Case 1a Differences Use subnet mask to determine that the destination is NOT on the same subnet Send outgoing frames to the local subnet’s GW Local gateway operations Receive the frame and remove the Ethernet header Determine the next node (via Router Table) Make a new frame and send it to the destination GW Destination gateway operations Remove the header, determine the destination (by destination IP address) Place the IP packet in a new Ethernet frame and send it to its final destination. Copyright 2005 John Wiley & Sons, Inc

Case 3: Unknown Address Operations (by the host) Determine the destination IP address Send a UDP packet to the local DNS server Local DNS server knows the destination host’s IP address Sends a DNS response back to the sending host Local DNS server does not know the destination IP address Send a second UDP packet to the next highest DNS host, and so on, until the destination host’s IP address is determined Follow steps in Case 2 Copyright 2005 John Wiley & Sons, Inc

TCP Connections Before any data packet is sent, a connection is established Use SYN packet to establish connection Use FIN packet to close the connection Handling of HTTP packets Old version: a separate TCP connection for each HTTP Request New version: Open a connection when a request (first HTTPP Request) send to the server Leave the connection open for all subsequent HTTP requests to the same server Close the connection when the session ends Copyright 2005 John Wiley & Sons, Inc

TCP/IP and Layers Host Computers Packets move through all layers Gateways, Routers Packet moves from Physical layer to Data Link Layer through the network Layer At each stop along the way Ethernet packets is removed and a new one is created for the next node IP and above packets never change in transit (created by the original sender and destroyed by the final receiver) Copyright 2005 John Wiley & Sons, Inc

Message Move Through Layers

Most organizations moving toward a single standard, TCP/IP Decreased cost of buying and maintaining network equipment Decreased cost of training networking staff Telephone companies (having large non-TCP/IP networks) moving toward TCP/IP Significant financial implications for telcos Significant financial implications of networking equipment manufacturers Copyright 2005 John Wiley & Sons, Inc

Wireless Local Area Networks
Chapter 7 Wireless Local Area Networks Copyright 2005 John Wiley & Sons, Inc

Wireless LANs (WLANs) Use radio or infrared frequencies to transmit signals through the air (instead of cables) Basic Categories Use of Radio frequencies (FOCUS of this chapter) 802.1x family of standards (aka, Wi-Fi) Use of Infrared frequencies (Optical transmission) Wi-Fi grown in popularity Eliminates cabling Facilitates network access from a variety of locations Airports, cafes, restaurants, etc., Facilitates for mobile workers (as in a hospital) Copyright 2005 John Wiley & Sons, Inc

Principal WLANs Technologies
IEEE b Standardization started after .11a, but finished before IEEE a First attempt to standardization of WLANs; more complicated than .11b IEEE g Bluetooth Also an IEEE standard Copyright 2005 John Wiley & Sons, Inc

IEEE b Reuses many Ethernet components Designed to connect easily to Ethernet a.ka., wireless Ethernet Also called Wi-Fi Marketing ploy; sounds like Hi-Fi Versions of .11b Direct Sequence Spread Spectrum (DSSS) Focus of this chapter (more popular) Frequency Hopping Spread Spectrum (FHSS) Copyright 2005 John Wiley & Sons, Inc

Versions of IEEE b Direct Sequence Spread Spectrum (DSSS) Uses the entire frequency band to transmit information Capable of data rates of up to 11 Mbps Fallback rates: 5.5, 2 and 1 Mbps. (Used when interference or congestion occurs) Dominates market place, because faster Frequency Hopping Spread Spectrum (FHSS) Divides the frequency band into a series of channels Then changes its frequency channel about every half a second, based on a pseudorandom sequence More secure, Only capable of data rates of 1 or 2 Mbps Copyright 2005 John Wiley & Sons, Inc

WLAN Topology Same as Ethernet Physical star Logical bus Use the same radio frequencies, so take turns using the network 10Base-T or 100Base-T Uses a NIC that transmits radio signals to the AP A wireless Access Point (AP) connected into an Ethernet Switch Copyright 2005 John Wiley & Sons, Inc

Components of WLANs Network Interface Cards Available for laptops as PCMCIA cards Available for desktops as standard cards Many laptops come with WLAN cards built in About feet max transmission range Access Points (APs) Used instead of hubs; act as a repeater Must hear all computers in WLAN Message transmitted twice Sender to AP, then AP to receiver Copyright 2005 John Wiley & Sons, Inc

More on the APs and NICs 3 separate channels available for b All devices using an AP must use the same channel WLAN functions as a shared media LAN Reduces the interference Users can roam from AP to AP Initially NIC selects a channel (thus an AP) Based on “strength of signal” from an AP During roaming, if NIC sees another AP with a stronger signal, attaches itself to this AP Usually a set of APs installed to provide geographical coverage and meet traffic needs NICs selects a less busy channel if its current channel becomes busy (too many users) Copyright 2005 John Wiley & Sons, Inc

Figures 7.2 and 7.3 will be used here Antennas used in WLANs Omni directional antennas Transmit in all directions simultaneously Used on most WLANs Dipole antenna (rubber duck) Transmits in all direction (vertical, horizontal, up, down) Directional antennas Project signal only in one direction Focused area; stronger signal; farther ranges Most often used on inside of an exterior wall To reduce the security issue A potential problem with WLANs Copyright 2005 John Wiley & Sons, Inc

WLAN Media Access Control
Uses CSMA/CA CA  collision avoidance A station waits until another station is finished transmitting plus an additional random period of time before sending anything May use two MAC techniques simultaneously Distributed Coordination Function (DCF) Also called “Physical Carrier Sense Method” Point Coordination Function (PCF) Also called “Virtual Carrier Sense Method” Optional: (can be set as “always”, “never”, or “just for certain frame sizes” Copyright 2005 John Wiley & Sons, Inc

Distributed Coordination Function
Relies on the ability of computers to physically listen before they transmit When a node wants to send a message: First listens to make sure that the transmitting node has finished, then Waits a period of time longer Each frame is sent using stop-and-wait ARQ By waiting, the listening node can detect that the sending node has finished and Can then begin sending its transmission ACK/NAK sent a short time after a frame is received, Message frames are sent a somewhat longer time after (ensuring that no collision will occur) Copyright 2005 John Wiley & Sons, Inc

Point Coordination Function (PCF)
Solves Hidden Node problem Two computers can not detect each other’s signals A computer is near the transmission limits of the AP at one end and another computer is near the transmission limits at the other end of the AP’s range Physical carrier sense method will not work Solution First send a Request To Send (RTS) signal to the AP Request to reserve the circuit and duration AP responds with a Clear To Send (CTS) signal, Also indicates duration that the channel is reserved Computer wishing to send begins transmitting Copyright 2005 John Wiley & Sons, Inc

Preamble of b Packets Used to mark the start of the packet Always transmitted at 1 Mbps Sub fields of Preamble Long preamble version 16 sync bytes of alternating 1’s and 0’s 1 byte of start of frame delimiter ( ) Short preamble version 7 sync bytes 1 byte of start of frame Copyright 2005 John Wiley & Sons, Inc

Physical Layer Convergence Protocol (PLCP)
Used to indicate data rates and packet length Transmitted at 1 Mbps (long preamble) or at 2 Mbps (short preamble) Fields of PLCP Signal rate (1 byte) Which of the four speeds to be used Service field (1 byte) Reserved for future use Length field (2 bytes) Length of the payload in 8-bit bytes Header error check field (2 bytes) CRC-16 (if any error found, packet is discarded) Copyright 2005 John Wiley & Sons, Inc

Fields of Payload Header
Frame control (2 bytes) Indicates version of the b protocol Contains any ACK/NAK and RTS/CTS signals Destination address (6 bytes) AP-NIC: Address of NIC; NIC-AP-NIC: Address of AP Address 3 (6 bytes) NIC-AP-NIC: Address of the NIC Source address (6 bytes) AP-NIC: Address of AP; NIC-AP-NIC: Address of NIC Sequence control (2 bytes) Contains packet number for error control Address 4 (6 bytes) Used only for NIC-NIC communications Copyright 2005 John Wiley & Sons, Inc

Data Transmission in PL
Via radio waves Analog medium Digital computer data transmitted using analog transmission (Translations done by NIC and AP) Frequency and bandwidth (range of frequencies) – GHz  83.5 MHz bandwidth in USA Transmission 83.5 MHz divided into 3 channels  22 MHz each (with 3 MHz guard bands between channels) Data capacity of the circuit: Number of bits sent on each symbol x symbol rate Max symbol rate: depends on bandwidth and SNR 22 MHz  22 million symbols/second (perfect conditions) Copyright 2005 John Wiley & Sons, Inc

Bit Transmission in DSSS
Each bit converted into a special code 8-bit or 11-bit code (designed to reduce interference) Called spreading a bit into many bits across spectrum 1-Mbps DSS Uses an 11-bit Barker sequence code Transmitted using binary phase shift keying (BPSK) (1 bit per symbol) 11 Mbps signaling rate  1 Mbps data rate 2-Mbps DSS Uses the same 11-bit code Transmits using Quadrature phase shift keying (QPSK) (2 bits per symbol) 11 Mbps signaling rate  2 Mbps data rate Copyright 2005 John Wiley & Sons, Inc

1Mbps DSSS with Barker code
>>>>>> Figure 7.5 goes here Copyright 2005 John Wiley & Sons, Inc

IEEE a Operates in a 5 GHz frequency range Total bandwidth is 300 MHz Faster data rates possible: Up to 54 Mbps 6, 9, 12, 18, 24, 36, 48, and 54 Mbps Uses the same topology as .11b Reduced range because of higher speed 50 meters ( 150 feet) Highest speed achievable within 15 meter Copyright 2005 John Wiley & Sons, Inc

IEEE a Coverage Provides 4-12 channels (depending on configuration) Important for coverage; takes more .11a AP to cover the same area (small range) Make it possible to locate many APs in the same area to increase capacity Figure 7.6 goes here Copyright 2005 John Wiley & Sons, Inc

802.11a Media Access Control Same as .11b Similar packet format Preamble and PLCP Header: transmitted at 6 Mbps PLCP parity bit field: used for error checking of header PLCP tail field: used as a pad to “byte” align the packet Payload service field: to sync circuitry in NIC and AP Copyright 2005 John Wiley & Sons, Inc

802.11a Data Transmission Similar to b; spreads its transmission over a wider spectrum Each of 12 channel’s bandwidth = 20 MHz Broken into 52 separate channels: KHz each, plus guard bands 48 channels for data (sent across all channels in parallel using Orthogonal Frequency Division Multiplexing (OFDM) 4 channels for control Copyright 2005 John Wiley & Sons, Inc

OFDM Versions 6-Mbps version of .11a Groups data into sets of 24 data bits Converts each group into an OFDM symbol of 48 bits Pattern chosen enables some error correction Transmit each symbol in one of 48 sub channels using BPSK sent at 250 KHz 24 data bits x 250 KHz  6 Mbps 9-Mbps version Groups data into sets of 36 bits Transmits each symbol using BPSK 36 data bits x 250 KHz  9 Mbps Copyright 2005 John Wiley & Sons, Inc

OFDM Versions (Cont.) 12-Mbps version Groups data into sets of 48 bits Transmit OFDM symbol using QPSK (2 bits per symbol) 48 bits x 250 KHz x 2 bits  12 Mbps 18-Mbps version Groups data into sets of 72 bits; uses QPSK 72 bits x 250 KHz x 2 bits  18 Mbps 24-Mbps version Groups data into sets of 96 bits Transmit OFDM symbol using QAM (4 bits per symbol) 96 bits x 250 KHz x 4 bits  24 Mbps Copyright 2005 John Wiley & Sons, Inc

OFDM Versions (Cont.) 36-Mbps version Groups data into sets of 128 bits; uses QAM Transmit OFDM symbol using QPSK (2 bits per symbol) 128 bits x 250 KHz x 4 bits  36 Mbps 48-Mbps version Groups data into sets of 192 bits Transmit OFDM symbol using 64-QAM (6 bits per symbol) 192 bits x 250 KHz x 6 bits  48 Mbps 54-Mbps version Groups data into sets of 216 bits; uses 64-QAM 216 bits x 250 KHz x 6 bits  54 Mbps Copyright 2005 John Wiley & Sons, Inc

IEEE g Designed to combine advantages of a and b Offers higher data rates (up to 54 Mbps) in 2.4 GHz band (as in .11b) with longer ranges Backward compatible with b .11b devices can interoperate with .11g APs Price to pay: when an .11g AP detects an .11b device, it prohibits .11g devices from operating at higher speeds Uses the same topology as .11b Provides 3-6 channels (depending on configuration) 54 Mbps rate obtained within 50 meter range Copyright 2005 John Wiley & Sons, Inc

802.11g Media Access Control Almost the same media and error control protocols as .11b Similar packet layout, except Preambles and headers transmitted at slower speeds (up to a maximum of 11 Mbps) Payload transmitted at higher speeds (up to a max of 54 Mbps) Data Transmission in the Physical Layer Same techniques in .11a and .11b Uses PSK, QPSK, and CCK to provide .11b rates Uses BPSK, QPSK, and QAM to provide .11a rates Copyright 2005 John Wiley & Sons, Inc

Bluetooth (IEEE ) A standard for Wireless Personal Area Network (WPAN) Provides networking in a very small area Up to 10 meters (current generation) Up to 100 meters (next generation) Includes small (1/3 of an inch square) and cheap devices designed to Replace short distance cabling between devices Keyboards, mouse, handsets, PDAs, etc Provides a basic data rate of 1 Mbps Can be divided into several voice and data channels Uses Frequency Shift Keying (FSK) for data transmission (1 bit per symbol) Copyright 2005 John Wiley & Sons, Inc

Bluetooth Topology Uses the term “piconet” to refer to a Bluetooth network Consists of 8 devices A “master” device controlling other devices, “slaves” Acts like an AP Selects frequencies and controls access All devices in a piconet share the same frequency range Copyright 2005 John Wiley & Sons, Inc

Bluetooth Media Access Control
Uses Frequency Hopping Spread Spectrum (FHSS) Available frequency range ( ) divided into 79 separate 1-MHz channels A data burst transmitted using one channel, next data burst uses the next channel, and so on. Channels changed based on a sequence and established by the slave and the master prior to the data transfers 1,600 channel change per second Also used to minimize interference A noisy channel avoided eventually Not compatible with b Potential interference problems (especially if many Bluetooth devices present close to .11b devices) Copyright 2005 John Wiley & Sons, Inc

Bluetooth Packet Formats
>>>Figure7.9 goes here Copyright 2005 John Wiley & Sons, Inc

Bluetooth Packet Fields/ Subfields
Access Code: to sync the sender and receiver Preamble: Alternating 1’s and 0’s Sync Bytes: bit patterns based on addresses and packet types Trailer: Alternating 1’s and 0’s Header: for address and error control Address: Slave’s address Type: Payload’s type (e.g., data, control etc.) Flow Control: 1 means continue, 0 means to stop ARQ ACK/NAK: 1 means ACK, 0 means NACK Sequence Number: packet number used for ARQ Header Error Check: CRC-8 for the header Copyright 2005 John Wiley & Sons, Inc

Bluetooth Packet Fields/Subfields
Payload Header Logical Channel: whether the payload has a data or control frame Flow Control: same as before (for a another software) Length: Payload’s length in bytes Future Use: Reserved Payload: Format depends on the type of data transmitted Payload trailer CRC-16 error check code Copyright 2005 John Wiley & Sons, Inc

Infrared Wireless LAN Require line of sight (LOS) to work (less flexible) Main advantage: reduced wiring usually mounted in fixed positions to ensure they will hit their targets New version: diffuse infrared, Operates without a direct LOS by bouncing the infrared signal off of walls Only able to operate within a single room and at distances of only about feet Copyright 2005 John Wiley & Sons, Inc

Effective Data Rates in WLANs
Maximum speed in bits the hardware layers can provide Depends on Nominal data rate, Error rate, Efficiency of data link layer protocol, and Efficiency of MAC protocol Error plays a greater role in WLANs Significant impact of interference on performance Causes frequent retransmissions, thus lower data rates Copyright 2005 John Wiley & Sons, Inc

Data Link Protocol Efficiency
Factors involved: Typical WLAN overhead: 51-bytes (with a short preamble) Packet size: Data packets: assume a 1500-byte for full length Control packets: ACK/NAK packets Transmission rates: Overhead bits transmission speeds Payload transmission speeds Assuming a mix of short and full length packets 85% average efficiency for b 75% average efficiency for a and g Copyright 2005 John Wiley & Sons, Inc

MAC Protocol Efficiency
Uses a controlled approach (PCF) Imposes more fixed delays initially when traffic is low Due to PCF’s permission based procedures Allows response time delays increases slowly up to 85-90% of capacity >>>>>>>>Figure goes here Copyright 2005 John Wiley & Sons, Inc

Effective Rate for a Computer*
802.11b 85% efficiency x 85% capacity x 11 Mbps = 9.6 Mbps 2 users: 9.6 Mbps / 2  4.8 Mbps per user 10 users: 9.6 Mbps/10  960 Kbps per user 802.11a 75% efficiency x 85% capacity x 54 Mbps = 34.4 Mbps 2 users: 34.4 Mbps / 2  17.2 Mbps per user 10 users: 34.4 Mbps/10  3.4 Mbps per user 802.11g * Under perfect conditions Copyright 2005 John Wiley & Sons, Inc

Effective Rate Estimates
Figure 7-12 goes here Copyright 2005 John Wiley & Sons, Inc

Costs 802.11b Decreasing cost of NICs and AP s 802.11a and g Newer technologies, higher costs Comparison with wired Ethernets (cost of .11b AP) = (cost of 10/100Base-T switch) (cost of .11b NIC) = $20 + (cost of 10/100Base-T NIC) No cost for cabling and its deployment in WLAN Wired Ethernet cable deployment cost: $50 - $400 Cheapest to install during construction of building For new buildings Wired LANs are less expensive Do not forget the need for mobility !! Copyright 2005 John Wiley & Sons, Inc

Best Practice Recommendations
Adopt g Will replace b and .11a Prices of .11g NICs and APs coming down Wireless vs. Wired 802.11g ~ 10Base-T Similar data rates for low traffic environment When mobility important  g Using WLAN as overlay network (over wired LAN) WLANs installed In addition to wired LANs To provide mobility for laptops, etc., To provide access in hallways, lunch rooms, etc., Copyright 2005 John Wiley & Sons, Inc

Physical WLAN Design More challenging than designing a traditional LAN Placement of APs: Locations chosen to: Provide coverage Minimize potential interference Begins with a site survey to determine Feasibility of desired coverage Measuring the signal strength from temporary APs Potential sources of interference Most common source: Number and type of walls Locations of wired LAN and power sources Estimate of number of APs required Copyright 2005 John Wiley & Sons, Inc

Physical WLAN Design Begin locating APs Place an AP in one corner Move around measuring the signal strength Place another AP to the farthest point of coverage AP may be moved around to find best possible spot Also depends on environment and type of antenna Repeat these steps several times until the corners are covered Then begin the empty coverage areas in the middle Allow about 15% overlap in coverage between APs To provide smooth and transparent roaming Set each AP to transmit on a different channel Copyright 2005 John Wiley & Sons, Inc

Multistory WLAN Design
Must include Usual horizontal mapping, and Vertical mapping to minimize interference from APs on different floors Figure 7.14 goes here Copyright 2005 John Wiley & Sons, Inc

WLAN Security Especially important for wireless network Anyone within the range can use the WLAN Finding a WLAN Move around with WLAN equipped device and try to pick up the signal Use special purpose software tools to learn about WLAN you discovered Wardriving – this type reconnaissance Warchalking – writing symbols on walls to indicate presence of an unsecure WLAN Copyright 2005 John Wiley & Sons, Inc

Types of WLAN Security Service Set Identifier (SSID) Required by all clients to include this in every packet Included as plain text Easy to break Wired Equivalent Privacy (WEP) Requires that user enter a key manually (to NIC and AP) Communications encrypted using this key Short key ( bits)  Easy to break by “brute force” Extensible Authentication Protocol (EAP) WEP keys created dynamically after correct login Requires a login (with password) to a server After logout, WEP keys discarded by the server Wi-Fi Protected Access (WPA) – new standard A longer key, changed for every packet Copyright 2005 John Wiley & Sons, Inc

Improving WLAN Performance
Similar to improving wired LANs Improving device performance Improving wireless circuit capacity Reducing network demand Copyright 2005 John Wiley & Sons, Inc

Improving WLAN Performance
Similar to improving wired LANs Improving device performance If g widely deployed, replace b cards with .11g cards (may be the cause for slow performance By high-quality cards and APs Improving wireless circuit capacity Upgrade to g Reexamine placement of APs Check sources of interference (other wireless devices operating in the same frequencies)) Use different type of antennas Reducing network demand w Copyright 2005 John Wiley & Sons, Inc

Improving WLAN Device Performance
If g widely deployed, replace b cards with .11g cards May be the cause for slow performance By high-quality cards and APs Better design Stronger signals, Longer ranges Copyright 2005 John Wiley & Sons, Inc

Improving Wireless Circuit Capacity
Upgrade to g Re-place APs Fewest walls between AP and devices Ceiling or high mounted to minimize obstacles On halls, not in closets Remove sources of interference Other wireless devices operating in the same frequencies Bluetooth devices, cordless phones, etc. Use different type of antennas Directional antennas in smaller range to get stronger signals (faster throughput) Copyright 2005 John Wiley & Sons, Inc

Reducing WLAN Demand Never place a serve in a WLAN Doubles the traffic between clients and server Since all communications ii through the AP Locate the server in the wired part of the network (ideally with a switched LAN) Place wired LAN jacks in commonly used locations If WLAN becomes a problem, users can switch to wired LAN easily Copyright 2005 John Wiley & Sons, Inc

WLANs becoming common place Access to internal data, any time, any place Better protection of corporate networks Public access through WLAN hotspots Competition with cell phone technologies New cell phone technologies (faster, longer ranges) Drastic price drops of WLAN devices Widespread Internet access via multiplicity of devices (PDAs, etc,) Development of new Internet applications New companies created; some old ones out of business Drastic increase in the amount of data flowing around Copyright 2005 John Wiley & Sons, Inc

Outline Components of Backbone networks Bridges, Routers, Gateways Backbone network architectures Backbone technologies Best practice backbone design Improving backbone performance Copyright 2005 John Wiley & Sons, Inc

Backbone Networks High speed networks linking an organization’s LANs Making information transfer possible between departments Use high speed circuits to connect LANs Provide connections to other backbones, MANs, and WANs Sometimes referred to as An enterprise network A campus-wide network Copyright 2005 John Wiley & Sons, Inc

Backbone Network Components
Network cable Functions in the same way as in LANs Optical fiber - more commonly chosen (provides higher data rates) Hardware devices Computers or special purpose devices used for interconnecting networks Bridges Routers Gateways Copyright 2005 John Wiley & Sons, Inc

Backbone Network Devices
Device Operates at Packets Physical Layer Data Link Layer Network Layer Bridge Data Link Layer Filtered using data link layer addresses Same or Different Same Same Router Network Layer Routed using network layer addresses Same or Different Same or Different Same Gateway Network Layer Routed using network layer addresses Same or Different Same or Different Same or Different Copyright 2005 John Wiley & Sons, Inc

Bridges Data link layer devices Connect LANs with the same Data Link and same Network layers Allows different types of cabling Operate in a similar way to layer 2 switches (learning bridges) Copyright 2005 John Wiley & Sons, Inc

Learning Bridges Operate in a similar way to layer 2 switches: Learn which computers are on each side of the bridge By reading the source addresses on incoming frames and recording this information in forwarding tables Data link layer devices Connecting similar type of networks But they can connect different types of cable Not popular anymore Losing market share to layer 2 switches as the latter become cheaper and more powerful Copyright 2005 John Wiley & Sons, Inc

Routers Operate at the network layer Connect LANS with different data link layer, but the same network layer protocol Allows different types of cabling Perform more processing than bridges or layer 2 switches Copyright 2005 John Wiley & Sons, Inc

Routers (Cont.) Operations Strip off the header and trailer of the incoming L2 frame Examine the destination address of the network layer Build a new frame around the packet Choose the “best” route for a packet (via routing tables) Send it out onto another network segment Compared to Bridges Perform more processing Process L3 messages (no changes made) Form new L2 messages for outgoing packets Processes only messages specifically addressed to it Copyright 2005 John Wiley & Sons, Inc

Gateways Also operate at network layer (like routers) Connect LANS with different data link layer and different network layer protocols Some operate at the application layer as well Copyright 2005 John Wiley & Sons, Inc

Other BB Network Devices
Multiprotocol routers Can handle several different protocols (no translation) In and out protocols must be the same Brouters Combine bridge and router functions Examine L2 addresses of all messages Can also process directly addressed (L2) messages Layer-3 switches Similar to L2 switches, but switch messages based on L3 addresses Can support many more simultaneous ports than routers Copyright 2005 John Wiley & Sons, Inc

Backbone Network Architectures
Identifies the way backbone interconnects LANs Defines how it manages packets moving through BB Fundamental architectures Bridged Backbones Routed Backbones Collapsed Backbones Rack-based Chassis-based Virtual LANs Single-switch VLAN Multiswitch VLAN Copyright 2005 John Wiley & Sons, Inc

Backbone Architecture Layers
Access Layer (not part of BB) Closest to the users; Backbone Design Layers Distribution Layer Connects the LANs together (often in one building Core Layer (for large campus/enterprise networks) Connects different BNs together (building to building) <<<<<<<< Figure 8.5 goes here Copyright 2005 John Wiley & Sons, Inc

Bridged Backbones Move packets between networks based on their data link layer addresses Cheaper (since bridges are cheaper than routers) and easier to install (configure) Just one subnet to worry about Change in one part may effect the whole network Performs well for small networks For large networks broadcast messages (e.g., address request, printer shutting down) can lower performance Formerly common in the distribution layer Declining due to performance problems Copyright 2005 John Wiley & Sons, Inc

Routed Backbones Move packets using network layer addresses Commonly used at the core layer Connecting LANs in different buildings in the campus Can be used at the distribution layer as well LANs can use different data link layer protocols Main advantage: LAN segmentation Each message stays in one LAN; unless addressed outside the LAN Easier to manage Main disadvantages Tend to impose time delays compared to bridging Require more management than bridges & switches Copyright 2005 John Wiley & Sons, Inc

Collapsed Backbone Most common type BB mainly used in
distribution layer A connection to the switch is a separate point-to-point circuit Star topology Copyright 2005 John Wiley & Sons, Inc

Collapsed Backbones Replaces the many routers or bridges of the previous designs Backbone has more cables, but fewer devices No backbone cable used; switch is the backbone. Advantages: Improved performance ( % higher) Simultaneous access; :switched” operations A simpler more easily managed network – less devices Two minor disadvantages Use more and longer cables Reliability: If the central switch fails, the network goes down. Copyright 2005 John Wiley & Sons, Inc

Rack-Based Collapsed Backbones
Figure 8-9 goes here Copyright 2005 John Wiley & Sons, Inc

Rack-Based Collapsed Backbones
Places all network equipment (hubs and switches) in one room (rack room) Easy maintenance and upgrade Requires more cable (but cables are cheap) Main Distribution Facility (MDF) or Central Distribution Facility Another name for the rack room Place where many cables come together Patch cables used to connect devices on the rack Easier to move computers among LANs Useful when a busy hub requires offloading Copyright 2005 John Wiley & Sons, Inc

Main Distribution Facility (MDF)
>>>> Figure 8.10 goes here Copyright 2005 John Wiley & Sons, Inc

Chassis-Based Collapsed Backbones
Use a “chassis” switch instead of a rack A collection of modules Number of hubs with different speeds L2 switches Example of a chassis switch with 710 Mbps capacity 5 10Base-T hubs, 2 10Base-T switches (8 ports each) 1 100Base-T switch (4 ports), 100Base-T router  ( 5 x 10) + (2 x 10 x 8) + (4 x 100) = 710 Mbps Flexible Enables users to plug modules directly into the switch Simple to add new modules Copyright 2005 John Wiley & Sons, Inc

Virtual LANs (VLANs) A new type of LAN-BN architecture Made possible by high-speed intelligent switches Computers assigned to LAN segments by software Often faster and provide more flexible network management Much easier to assign computers to different segments More complex and so far usually used for larger networks Basic VLAN designs: Single switch VLANs Multi-switch VLANs Copyright 2005 John Wiley & Sons, Inc

Single Switch VLAN Collapsed Backbone
acting as a large physical switch Computers assigned to different LANs by software Switch Copyright 2005 John Wiley & Sons, Inc

Types of Single Switch VLANs
Port-based VLANs (Layer 1 VLANs) Use physical layer port numbers on the front of the VLAN switch to assign computers to VLAN segments Use a special software to tell the switch about the computer - port number mapping MAC-based VLANs (Layer 2 VLANs) Use MAC addresses to form VLANs Use a special software to tell the switch about the computer - MAC address mapping Simpler to manage Even if a computer is moved and connected to another port, its MAC address determines which LAN it is on Copyright 2005 John Wiley & Sons, Inc

Types of Single Switch VLANs
IP-based VLANs (Layer 3 VLANs, protocol based VLANs) Use IP addresses of the computers to form VLANs Similar to MAC based approach (use of IP instead of MAC address) Application-based VLANs (Layer 4 VLANs, policy-based VLANs) Use a combination of the type of application (Indicated by the port number in TCP packet) and The IP address to form VLANs Complex process to make assignments Allow precise allocation of network capacity Copyright 2005 John Wiley & Sons, Inc

Multi-switch VLAN-Collapsed Backbone

Multi-switch VLAN Operations
Inter-switch protocols Must be able to identify the VLAN to which the packet belongs Use IEEE 802.1q (an emerging standard) When a packet needs to go from one switch to another 16-byte VLAN tag inserted into the packet by the sending switch When the IEEE 802.1q packet reaches its destination switch Its header (VLAN tag) stripped off and Ethernet packet inside is sent to its destination computer Copyright 2005 John Wiley & Sons, Inc

VLAN Operating Characteristics
Advantages of VLANs Faster performance Precise management of traffic flow Ability to allocate resources to different type of applications Traffic prioritization (via 802.1q VLAN tag) Include in the tag: a priority code based on 802.1p Can have QoS capability at MAC level Similar to RSVP and QoS capabilities at network and transport layers Drawbacks Cost Management complexity Copyright 2005 John Wiley & Sons, Inc

Backbone Technologies
Gigabit Ethernet Fiber Distributed Data Interface (FDDI) Asynchronous Transfer Mode (ATM) Copyright 2005 John Wiley & Sons, Inc

FDDI A set of standards designed in 80’s for MANs (ANSI X3T9.5) Also used as BB and LAN technologies Limited future Gigabit Ethernet’s strong presence A ring network operating at 100 Mbps over fiber cables Assumes a mix of 1,000 stations and 200 Km path With repeaters at every 2 Km Uses 2 counter rotating rings: primary and secondary Data on the primary; secondary used as backup Copyright 2005 John Wiley & Sons, Inc

Managing a Broken Ring in FDDI
>>>> Figure 8.16 If a ring is broken, the ring can still operate in a limited fashion Copyright 2005 John Wiley & Sons, Inc

FDDI Media Access Control
Uses a controlled access token passing scheme Sending computer Wait for the token, when receive it Attach the packet to the token and transmit them Receiving computer See if there is a packet attached to the token If there is  process the packet If it needs to transmit a packet  follow the steps above If no packet to send  simply transmit the token to the next computer Very reliable and provide adequate response time until it almost reaches saturation at 100 Mbps Copyright 2005 John Wiley & Sons, Inc

ATM Originally designed for use in WAN Often used now in BNs Standardized; simple to connect BNs and WANs Also called cell relay Includes Layer 3, Layer 2 and Layer 1 technologies in the specifications Compatible with TCP/IP and Ethernet as if ATM was Layer 2 technology A connection oriented technology ATM switches Provide point-to-point full duplex circuits at 155 Mbps (622 Mbps for switch-to-switch) Copyright 2005 John Wiley & Sons, Inc

ATM vs. Ethernet Packet format: Uses fixed-length packets (cells) of 53 bytes: 5-byte header, 48 byte data Designed to make switching faster (in hardware) Error Checking Error checking done for header only (not on data) If error detected, cell is discarded Addressing Uses a virtual channel(VC) between sender and receiver All cells use VC Identifier as addresses QoS (prioritized transmissions) Each VC assigned a specific class of service with a priority Copyright 2005 John Wiley & Sons, Inc

Virtual Channels in ATM
Identified by a two-part number Path number Circuit number within that path A physical port on a switch may have many paths A path may have many circuits A switch may have thousands of VCs A VC table is used to map the connections which can be established either: Permanently: Permanent Virtual Circuit (PVC) Temporarily: Switched Virtual Circuit (SVC) Deleted when the connection is not needed Copyright 2005 John Wiley & Sons, Inc

Addressing and Forwarding in ATM
When a cell arrives, switch checks the cell’s VC identifier at the table and determines where to send it . >>>Figure 8.17 goes here Copyright 2005 John Wiley & Sons, Inc

Approaches of Using ATM in Backbone
LAN Emulation (LANE) Breaking LAN frame into 48-byte long blocks and transmit them in an ATM cell Called encapsulation and done by edge switches Reassembling done at the destination edge switch and LAN frame is sent to the LAN Requires translating of MAC addresses to VC Identifiers (assuming VCs are setup already) Performance suffers due to encapsulation and connection management Multiprotocol over ATM (MPOA)- LANE extension Uses IP addresses in addition to MAC addresses If same subnet, use MAC address; otherwise use IP ATM backbone operating like a network of brouters Copyright 2005 John Wiley & Sons, Inc

Best Practice Backbone Design
Architectures Performance and cost  Collapsed backbone VLANs closer; but not mature enough Efficiency of data rates Data Link Protocol Efficiency FDDI with 99%: Overhead 29 bytes; up to 4500 byte data ATM with about 87%: Overhead: 5 bytes over 53 byte cell MAC Efficiency Copyright 2005 John Wiley & Sons, Inc

FDDI MAC Efficiency Uses token passing controlled access Imposes more fixed-cost delays initially in low traffic Increases response times only slowly up to 90-95% nominal capacity Total effective data rate = 89 Mbps 99% efficiency x 90% capacity x 100 Mbps >>>> Fig 8.19 goes here Copyright 2005 John Wiley & Sons, Inc

ATM MAC Efficiency Uses full duplex transmission Efficiency ~ 100% of capacity Effective data rate = 135 Mbps each direction simultaneously 87% efficiency x 100% capacity x 155 Mbps Total for both directions: 270 Mbps An ATM network with 622 Mbps circuits Provides 540 Mbps capacity each direction  1080 Mbps total Copyright 2005 John Wiley & Sons, Inc

Conversion between Protocols
Both requires conversion from/to Ethernet frames FDDI uses translation Remove Ethernet frame; replace it with FDDI frame Decreases efficiency 10-20% Actual total effective rate of FDDI  70 Mbps ATM uses encapsulation Segment and surround Ethernet frames with ATM cell headers  Generally faster MAC Addresses must be translated to VC Identifiers and VC management  30-40% decreased efficiency Actual total effective rate of ATM  80 Mbps each direction (160 Mbps total) Copyright 2005 John Wiley & Sons, Inc

Effective Data Rates of BB Technologies
>>>Fig 8-20 goes here Copyright 2005 John Wiley & Sons, Inc

Recommendations for BB Design
Best architecture Collapsed backbone or VLAN Best technology Gigabit Ethernet Ideal design A mixture of layer-2 and layer-3 Ethernet switches Access Layer 10/100Base-T Later 2 switches with cat5e or cat6 Distribution Layer 100base-T or 1000BaseT/F Layer 3 switches Core Layer Layer 3 switches running 10GbE or 40GBe Copyright 2005 John Wiley & Sons, Inc

Best Practice BB Design
>>>>>Fig 8-21 goes here Copyright 2005 John Wiley & Sons, Inc

Improving Backbone Performance
Improve computer and device performance Upgrade them to faster devices Use faster routing protocols Static routing is faster for small networks Use gigabit Ethernet as BB (eliminate translations) Increase memory in devices Improve circuit capacity Upgrade to a faster circuit; Add additional circuits Replace shared circuit BB with a switched BB Reduce network demand Restrict applications that use a lot of network capacity Reduce broadcast messages (placing filters at switches) Copyright 2005 John Wiley & Sons, Inc

Increased traffic at backbone due to faster technologies May requires that BN be replaced  Design BN to be easily upgradeable FDDI and ATM becoming as legacy technologies Vendors stopping the production of these  Begin to invest more funds to replace these Ethernet moving into Backbone extensively One standard technology used for both LANs and BN  Cheaper equipment; Easier management Copyright 2005 John Wiley & Sons, Inc

Metropolitan and Wide Area Networks
Chapter 9 Metropolitan and Wide Area Networks Copyright 2005 John Wiley & Sons, Inc

Outline Introduction Circuit Switched Networks Dedicated Circuit Networks Packet Switched Networks Virtual Private Networks Best practice MAN/WAN design Improving MAN and WAN Performance Copyright 2005 John Wiley & Sons, Inc

Introduction Metropolitan area networks (MANs) Span from 3 to 30 miles and connect backbone networks (BNs) and LANs Wide area networks (WANs) Connect BNs and MANs across longer distances, often hundreds of miles or more Typically built by using leased circuits from common carriers such as AT&T Most organizations cannot afford to build their own MANs and WANs, Copyright 2005 John Wiley & Sons, Inc

Introduction (Cont.) Focus of the Chapter Examine MAN/WAN architectures and technologies from a network manager point of view Focus on services offered by common carriers (in North America), and how they can be used to build networks Regulation of services Federal Communications Commission (FCC) in the US Canadian Radio Television and Telecomm Commission (CRTC) in Canada Public Utilities Commission (PUC) in each state Common Carriers Local Exchange Carriers (Less) like Verizon, Bell South Interexchange Carriers (IXCs) like AT&T Copyright 2005 John Wiley & Sons, Inc

Services Used by MANs/WANs
Circuit Switched Network Services Dedicated Circuit Networks Services Packet Switched Networks Services Virtual Private Networks Services Copyright 2005 John Wiley & Sons, Inc

Circuit Switched Services
Oldest and simplest MAN/WAN approach Uses the Public Switched Telephone Network (PSTN) i.e., telephone networks Provided by common carriers like AT&T and Ameritech Basic types in use today: POTS (Plain Old Telephone Service) Via use of modems to dial-up and connect to ISPs ISDN (Integrated Services Digital Network ) Copyright 2005 John Wiley & Sons, Inc

Basic Architecture of Circuit Switched Services
“Cloud” architecture Simpler design: What happens inside of network is hidden from the user A computer using modem dials the number of a another computer and creates a temporary circuit Can be expensive (connection and traffic based payment) When session is completed, circuit is disconnected. Copyright 2005 John Wiley & Sons, Inc

POTS based Circuit Switched Services
Use regular dial-up phone lines and a modem Modem used to call another modem Once a connection is made, data transfer begins Commonly used to connect to the Internet by calling an ISP’s access point Wide Area Telephone Services (WATS) Wholesale long distance services used for both voice and data Users buy so many hours of call time per month (e.g., 100 hours per month) for one fixed rate Copyright 2005 John Wiley & Sons, Inc

ISDN based Circuit Switched Services
Combines voice, video, and data over the same digital circuit Sometimes called narrowband ISDN Provides digital dial-up lines (each requires): An “ISDN modem” which sends digital transmissions is used Also called: Terminal Adapter (TA) An ISDN Network Terminator (NT-1 or NT-2) Each NT needs a unique Service Profile Identifier (SPID) Acceptance has been slow Lack of standardization, different interpretations. and relatively high cost ISDN: I Still Don’t Know Copyright 2005 John Wiley & Sons, Inc

Types of ISDN Services Basic rate interface (BRI) Basic access service or 2B+D Two 64 Kbps bearer ‘B’ channels (for voice or data) One 16 Kbps control signaling ‘D’ channel Can be installed over existing telephones lines (if less than 3.5 miles) Requires BRI specific end connections Primary rate interface (PRI) Primary access service or 23B+D Twenty three 64 Kbps ‘B’ channels One 64 Kbps ‘D’ channel (basically T-1 service) Requires T1 like special circuit Copyright 2005 John Wiley & Sons, Inc

Broadband ISDN A circuit-switched service but it uses ATM to move data Backwardly compatible with ISDN. B-ISDN services offered: Full duplex channel at Mbps Full duplex channel at Mbps Asymmetrical service with two simplex channels (Upstream: Mbps, downstream: Mbps) Copyright 2005 John Wiley & Sons, Inc

Circuit Switched Services
Simple, flexible, and inexpensive When not used intensively Main problems Varying quality Each connection goes through the regular telephone network on a different circuit, Low Data transmission rates Up to 56 Kbps for POTS, and up to 1.5 Mbps for ISDN An alternative Use a private dedicated circuit Leased from a common carrier for the user’s exclusive use 24 hrs/day, 7 days/week Copyright 2005 John Wiley & Sons, Inc

Dedicated Circuits Leased full duplex circuits from common carriers Used to create point to point links between organizational locations Routers and switches used to connect these locations together to form a network Billed at a flat fee per month (with unlimited use of the circuit) Require more care in network design Basic dedicated circuit architectures Ring, star, and mesh Dedicated Circuit Services T carrier services Synchronous Optical Network (SONET) services Copyright 2005 John Wiley & Sons, Inc

Basic Architecture of Dedicated Circuit Services
>>>>>> Fig 9.2 goes here Equipment installed at the end of dedicated circuits CSU/DSU: Channel Service Unit / Data Service Unit WAN equivalent of a NIC in a LAN May also include multiplexers Copyright 2005 John Wiley & Sons, Inc

Ring Architecture Reliability Messages can be rerouted around the failed link (Data can flow in both directions (full-duplex circuits)) With the expense of dramatically reduced performance Performance Messages need to travel through many nodes before reaching their destination Copyright 2005 John Wiley & Sons, Inc

central routing computer Copyright 2005 John Wiley & Sons, Inc
Star Architecture Easy to manage Central computer routes all messages in the network Reliability Failure of central computer brings the network down Failure of any circuit or computer affects one site only Performance Central computer becomes a bottleneck under high traffic central routing computer Copyright 2005 John Wiley & Sons, Inc

Mesh Architectures Combine performance benefits of ring and star networks Use decentralized routing, with each computer performing its own routing Impact of losing a circuit is minimal (because of the alternate routes) More expensive than setting up a star or ring network. Setting up alternate routes between computers Full mesh Expensive, seldom used Partial mesh More practical Copyright 2005 John Wiley & Sons, Inc

T-Carrier Services Most commonly used dedicated digital circuits in North America Units of the T-hierarchy DS-0 (64 Kbps); Basic unit T-1 (a.k.a. DS-1) (1.544 Mbps) Allows 24 simultaneous 64 Kbps channels which transport data or voice messages using PCM T-2 (6.312 Mbps) multiplexes 4 T-1 circuits T-3 ( Mbps); 28 T-1 capacity T-4 ( Mbps); 178 T-1 capacity (672 DS-0 channels) Fractional T-1, (FT-1) offers a portion of a T-1 Copyright 2005 John Wiley & Sons, Inc

T-Carrier Digital Hierarchy
T-Carrier Designation DS Designation Data Rate T-1 T-2 T-3 T-4 DS-0 DS-1 DS-2 DS-3 DS-4 64 kbps 1.544 Mbps 6.312 Mbps Mbps Mbps Copyright 2005 John Wiley & Sons, Inc

Synchronous Optical Network (SONET)
ANSI standard for optical fiber transmission in Gbps range Similar to ITU-T-based, synchronous digital hierarchy (SDH) SDH and SONET can be easily interconnected SONET hierarchy Begins with OC-1 (optical carrier level 1) at Mbps Each succeeding SONET hierarchy rate is defined as a multiple of OC-1 Copyright 2005 John Wiley & Sons, Inc

SONET Digital Hierarchy
SONET Designation SDH Designation Data Rate OC-1 OC-3 OC-9 OC-12 OC-18 OC24 OC-36 OC-48 OC-192 STM-1 STM-3 STM-4 STM-6 STM-8 STM-12 STM-16 51.84 Mbps Mbps Mbps Mbps Mbps 1.244 Gbps 1.866 Gbps 2.488 Gbps 9.952 Gbps Copyright 2005 John Wiley & Sons, Inc

Packet Switched Services
In both circuit switched and dedicated services A circuit established between two computers Solely assigned for use only between these two computers Data transmission provided only between these two computers No other transmission possible until the circuit is closed Packet switched services Enable multiple connections to exist simultaneously between computers over the same physical circuits User pays a fixed fee for the connection to the network plus charges for packets transmitted Copyright 2005 John Wiley & Sons, Inc

Basic Architecture of Packet Switched Services
Packet assembly/ disassembly device (PAD). Owned by the customer or the common carrier Users buy a connection into the common carrier network, and connect via a PAD Point-of-Presence (POP) leased dedicated circuits Copyright 2005 John Wiley & Sons, Inc

Packet Switching Interleave packets from separate messages for transmission Most data communications consists of short burst of data Packet switching takes advantage of this burstiness Interleaving bursts from many users to maximize the use of the shared network >>>>> Fig 9.10 goes here Copyright 2005 John Wiley & Sons, Inc

Packet Routing Methods
Describe which intermediate devices the data is routed through Connectionless (Datagram) Adds a destination and sequence number to each packet Individual packets can follow different routes Packets reassembled at destination (by using their sequence numbers) Connection Oriented (Virtual Circuit (VC)) Establishes an end-to-end circuit between the sender and receiver (before the packets sent) All packets for that transmission take the same route over the virtual circuit established Same physical circuit can carry many VCs Copyright 2005 John Wiley & Sons, Inc

Types of Virtual Circuits
Permanent Virtual Circuit (PVCs) Established for long duration (days or weeks) Changed only by the network manager More commonly used Packet switched networks using PVCs behave like a dedicated circuit networks Switched Virtual Circuit (SVC) Established dynamically on a per call basis Disconnected when the call ends Copyright 2005 John Wiley & Sons, Inc

Data Rates of Virtual Circuits
Users specify the rates per PVC via negotiations Committed information rate (CIR) Guaranteed by the service provider Packets sent at rates exceeding the CIR are marked discard eligible (DE), Discarded if the network becomes overloaded Maximum allowable rate (MAR) Sends data only when the extra capacity is available Copyright 2005 John Wiley & Sons, Inc

Packet Switched Service Protocols
X.25 Asynchronous Transfer Mode (ATM) Frame Relay Switched Multimegabit Data Service (SMDS) Ethernet/IP packet networks Copyright 2005 John Wiley & Sons, Inc

X.25 Oldest packet switched service A standard developed by ITU-T Offers SVC and PVC services Uses LAPB and PLP protocols at the data link and network layers, respectively Requires protocol translations at PADs (for those users who use different protocols at their LANs) A reliable protocol (it performs error control and retransmits bad packets) Widely used in Europe Not in widespread use in North America Low data rates (64 Kbps) (available now at Mbps) Copyright 2005 John Wiley & Sons, Inc

Asynchronous Transfer Mode (ATM)
Newer than X.25; also standardized ATM in MAN/WAN similar to ATM technology discussed for BNs Similar to X.25 Provides packet switching service Different than X.25: Operating characteristics Performs encapsulation (no translation) of packets Provides no error control (an unreliable protocol) Provides extensive QoS information Scaleable (easy to multiplex ATM circuits onto much faster ones) Copyright 2005 John Wiley & Sons, Inc

Error Control in X.25 vs. ATM
Error control in ATM is handled typically the transport layer (providing end-to-end communications) ACKs sent immediately by each node ACKs sent by final destination Copyright 2005 John Wiley & Sons, Inc

ATM Features Uses fixed length, 53 byte “cells” 5 bytes of overhead and 48 bytes of user data More suitable for real time transmissions. Provides extensive QoS information Enables setting of precise priorities among different types of transmissions (i.e. voice, video & ) Data Rates Same rates as SONET: 51.8, 466.5, Mpbs New versions: T1 ATM (1.5 Mbps), T3 ATM (45 Mbps) Copyright 2005 John Wiley & Sons, Inc

Frame Relay Another standardized technology Faster than X.25 but slower than ATM Encapsulates packets Packets delivered unchanged through the network Unreliable, like ATM Up to the end-points to control the errors NO QoS support (under development) Common CIR speeds: 56, 128, 256, 384 Kbps, 1.5, 2, and 45 Mbps Copyright 2005 John Wiley & Sons, Inc

SMDS A non-standardized technology Developed by Telcordia for local phone companies Unreliable, like ATM Encapsulates packets Originally developed for MANs, but could be used for WANs as well Transmission speeds offered: 56 Kbps to 45 Mbps Uncertain future Not standardized; competition from FR, ATM, and others Copyright 2005 John Wiley & Sons, Inc

Ethernet/IP Packet Networks
Offer Ethernet/IP packet services for building MAN/WAN networks Gigabit Ethernet fiber optic networks (bypassing common carrier network) Currently offer CIR speeds from 1 Mbps to 1 Gbps at 1/4 the cost of more traditional services No need to translate LAN protocol (Ethernet/IP) to the protocol used in MAN/WAN services X.25, ATM, Frame Relay and SMDS use different protocols requiring translation from/to LAN protocols Emerging technology; expect changes Copyright 2005 John Wiley & Sons, Inc

Virtual Private Networks
Provides equivalent of a private packet switched network over public Internet Use PVCs (tunnels) that run over the Internet Appear to the user as private networks Encapsulate the packets sent over these tunnels Using special protocols that also encrypt the IP packets they enclose Provides low cost and flexibility Uses Internet; Can be setup quickly Disadvantages of VPNs: Unpredictability of Internet traffic Lack of standards for Internet-based VPNs, so that not all vendor equipment and services are compatible Copyright 2005 John Wiley & Sons, Inc

VPN Architecture ISP Access Server VPN Device leased circuits Office Telephone Line VPN Device Employee’s Home Internet Backbone VPN Tunnel VPN Tunnel Office VPN Device VPN is transparent to the users, ISP, and the Internet as a whole; It appears to be simply a stream of packets moving across the Internet Backbone Copyright 2005 John Wiley & Sons, Inc

VPN Encapsulation of Packets
Packet from the client computer Packet in transmission through the Internet PPP IP TCP SMTP ATM IP L2TP PPP IP TCP SMTP ISP L2TP: Layer 2 Tunneling Protocol (An emerging VPN Layer-2 access protocol) Telephone Line Access Server VPN Device Employee’s Home Packet from the VPN VPN Tunnel PPP IP TCP SMTP Outgoing packets from the VPN are sent through specially designed routers or switches. Internet VPN Device Access Server VPN Encapsulation of Packets Backbone Copyright 2005 John Wiley & Sons, Inc

VPN Types Intranet VPN Provides virtual circuits between organization offices over the Internet Extranet VPN Same as an intranet VPN except that the VPN connects several different organizations, e.g., customers and suppliers, over the Internet Access VPN Enables employees to access an organization's networks from remote locations Copyright 2005 John Wiley & Sons, Inc

MAN/WAN Design Practices
Difficult to recommend best practices Services, not products, being bought Fast changing environment with introduction of new technologies and services from non-traditional companies Factors used Effective data rates and cost Reliability Network integration Design Practices Start with flexible packet switched service Move to dedicated circuit services, once stabilized May use both: packet switched services as backup Copyright 2005 John Wiley & Sons, Inc

Recommendations for the Best MAN/WAN Practices
>>>>>>>>>Fig 9-16 goes here Copyright 2005 John Wiley & Sons, Inc

Improving MAN/WAN Performance
Handled in the same way as improving LAN performance By checking the devices in the network, By upgrading the circuits between computers By changing the demand placed on the network Copyright 2005 John Wiley & Sons, Inc

Improving Device Performance
Upgrade the devices (routers) and computers that connect backbones to the WAN Select devices with lower “latency” Time it takes in converting input packets to output packets Examine the routing protocol (static or dynamic) Dynamic routing Increases performance in networks with many possible routes from one computer to another Better suited for “bursty” traffic Imposes an overhead cost (additional traffic) Reduces overall network capacity Should not exceed 20% Copyright 2005 John Wiley & Sons, Inc

Improving Circuit Capacity
Analyze the traffic to find the circuits approaching capacity Upgrade overused circuits Downgrade underused circuits to save cost Examine why circuits are overused Caused by traffic between certain locations Add additional circuits between these locations Capacity okay generally, but not meeting peak demand Add a circuit switched or packet switched service that is only used when demand exceeds capacity Caused by a faulty circuit somewhere in the network Replace and/or repair the circuit Make sure that circuits are operating properly Copyright 2005 John Wiley & Sons, Inc

Reducing Network Demand
Determine impact on network Require a network impact statement for all new application software Use data compression of all data in the network Shift network usage From peak or high cost times to lower demand or lower cost times e.g., transmit reports from retail stores to headquarters after the stores close Redesign the network Move data closer to applications and people who use them Use distributed databases to spread traffic across Copyright 2005 John Wiley & Sons, Inc

Changing role of networking and telecom managers Increased and mostly digitized data transmission causing the merger of these positions Changing technology Increasing dominance of VPNs, Frame Relay and Ethernet/IP Decreasing cots of setting up MANs/WANs Changing vendor profiles From telecom vendors to vendors with Ethernet and Internet experiences Copyright 2005 John Wiley & Sons, Inc

Internet Most used network in the world Not one network, but a network of networks Made up of thousands of networks of National and state government agencies, Non-profit organizations and for-profit companies. A rigidly controlled club To exchange data, these networks must agree to use Internet protocols TCP/IP MUST be supported by all networks Unrestricted applications and contents Developed freely Copyright 2005 John Wiley & Sons, Inc

Internet’s Hierarchical Structure
National Internet Service Providers (ISPs) Provide services to their customers and sell access to regional ISPs and local ISPs Regional ISPs Connect with National ISPs Provide services to their customers and sell access to local ISPs Local ISPs Connected to National or Regional ISPs Sell access to individuals Copyright 2005 John Wiley & Sons, Inc

Internet’s Access Points
Network Access Points (NAPs) Connect National ISPs together Sometimes large regional and local ISPs also have access directly to NAPs Indiana University, for example, which provides services to about 40,000 individuals, connects directly to the Chicago NAP About a dozen NAPs in the U.S. Run by common carriers such as Sprint and AT&T Metropolitan Area Exchanges (MAEs) Connect Regional ISPs together About 50 such MAEs in the U.S. today Copyright 2005 John Wiley & Sons, Inc

Basic Internet Architecture

Packet Exchange Charges
Peering ISPs at the same level usually do not charge each other for exchanging messages Higher level ISPs charge lower level ones National ISPs charge regional ISPs which in turn charge local ISPs Local ISPs charge individuals and corporate users for access Copyright 2005 John Wiley & Sons, Inc

Connecting to an ISP Done by through ISP’s Point of Presence (POP) A place ISP provides service to its customers Individual users Typically through a dial-up line using the PPP protocol Handled by the ISP’s modem pool Userid and password checked by Remote Access Server (RAS) Once logged in, the user can send packets over the phone line Corporate users Typically access the POP using a T-1, T-3 or ATM OC-3 connections provided by a common carrier Cost = ISP charges + circuit charges Copyright 2005 John Wiley & Sons, Inc

Inside an ISP POP Individual Dial-up Customers ISP Point-of Presence ISP POP Modem Pool ISP POP Corporate T1 Customer T1 CSU/DSU Layer-2 Switch ATM Switch Corporate T3 Customer ISP POP T3 CSU/DSU Remote Access Server Corporate OC-3 Customer ATM Switch NAP/MAE Copyright 2005 John Wiley & Sons, Inc

Inside an Internet NAP (Chicago)
One of the busiest (4 Gbps; 140 ISPs) ATM Switch Route Server Router ISP A ISP B ISP C ISP D ISP E ISP F Used to exchange routing information through BGP Copyright 2005 John Wiley & Sons, Inc

Internet Backbones in 2002 Backbone circuits for national ISPs OC-48 and OC-192 (10 Gbps) becoming common To be converted to OC-192 (10 Gbps) by 2005 OC-768 (40 Gbps) and use OC-3072 (160 Gbps) in experiment stage Aggregate Internet traffic Growing rapidly Expected to reach 40 Terabits per second (Tbps) by 2007. NAPs and MAEs becoming bottlenecks Requiring larger and larger switches Copyright 2005 John Wiley & Sons, Inc

Sprint’s Internet Backbone
A national ISP in North America Circuits: mostly ATM OC-12; few OC-48 and OC-192 >>>> Fig 10.4 goes here Copyright 2005 John Wiley & Sons, Inc

Internet Access Technologies
Most commonly used 56K dial-up lines (individuals) T1 or T3 lines into ISPs (organizations) New access technologies Commonly called “broadband access” Provide higher speed access Digital Subscriber Line (DSL) Cable Modems Fixed Wireless (including satellite access) Mobile Wireless (WAP) Copyright 2005 John Wiley & Sons, Inc

Digital Subscriber Line (DSL)
A family of point-to-point technologies Designed to provide high speed data transmission over traditional telephone lines Traditional telephone lines (local loop) Limited capacity due to telephone and switching equipment at the end offices Constrained by 4 KHz voice channel Much higher bandwidth possible (with new technology based equipment  DSL) Requires changing telephone equipment; not rewiring the local loop Not available in all locations in the US More wide spread in Asia, Europe and Canada Copyright 2005 John Wiley & Sons, Inc

Voice Telephone Network Copyright 2005 John Wiley & Sons, Inc
DSL Architecture Customer Premises Local Carrier End Office DSL Modem Line Splitter Main Distribution Frame Voice Telephone Network Local Loop Hub Telephone ATM Switch ISP POP Computer DSL Access Multiplexer Computer Customer Premises ISP POP ISP POP ISP POP Customer Premises Copyright 2005 John Wiley & Sons, Inc

Types of DSL Asymmetric DSL (ADSL) Uses three FDM channels 4 KHz analog voice channel A simplex data channel for downstream traffic A slower full-duplex data channel for Upstream traffic Size of digital channels Depends on the distance (CPE-Office) (up to 18,000 ft) Most common (T1): 1.5 Mbps down; 384 Kbps up Very high data rate DSL (VDSL) Designed for local loops of 4500 ft or less (1000 ft ideal) Also uses three FDM channels as in ADSL Size of digital channels (distance sensitive) Most common (1/4OC1): 12 Mbps down; 1.6 Mbps up Copyright 2005 John Wiley & Sons, Inc

ADSL Data Rates Type Maximum Length of Local Loop Maximum Downstream Rate Maximum Upstream Rate T1 18,000 feet 1.5 Mbps 384 Kbps E1* 16,000 feet 2.0 Mbps T2 12,000 feet 6.1 Mbps E2* 9,000 feet 8.4 Mbps 640 Kbps * E1 and E2 are the European standard services similar to T1 and T2 services in North America Copyright 2005 John Wiley & Sons, Inc

Cable Modems A digital service offered by cable television companies Data Over Cable Service Interface Specifications (DOCSIS) Most common protocol used for cable modems Not a formal standard Offers vary (depends on the quality of cable plant) In theory: downstream: 27-55Mbps; upstream: 2-10 Mpbs Typical: downstream: Mbps; upstream 0.2 – 2 Mbps A few cable companies offer downstream services only Upstream communications using regular telephone lines Copyright 2005 John Wiley & Sons, Inc

Cable Modem Architecture
Similar to DSL (with one main difference): DSL: point-to-point technology Cable modems: use shared multipoint circuits All messages on the circuit heard by all computers on the circuit  security issue 300 – 1000 customers per cable segment Type of equipment used Cable Modem Termination System (CMTS) Used for upstream traffic only Converts data from DOCSIS to Internet protocols Fiber Node with an Optical Electrical (OE) converter Combiner (for downstream traffic only) Combines Internet traffic with TV video traffic Copyright 2005 John Wiley & Sons, Inc

Basic Cable Modem Architecture
Cable Company Distribution Hub Cable Company Fiber Node Customer Premises Cable Modem Cable Splitter TV Video Network Downstream Combiner Optical/ Electrical Converter Upstream Hub TV Router Shared Coax Cable System Cable Company Fiber Node Computer Cable Modem Termination System Computer ISP POP Customer Premises Customer Premises Copyright 2005 John Wiley & Sons, Inc

Fixed Wireless Requires “line of sight” access between transmitters Requires tall buildings and towers Common use: provide Internet access to multi-tenant buildings (apartment buildings, hotels, etc.,) Types of FWA Point-to-point types Used to connect only two locations Point-multipoint types Allow access by a limited number of stations Designed as an alternative to DSL, cable modems Data access speeds Range from 1.5 to 11 Mbps Copyright 2005 John Wiley & Sons, Inc

Mobile Wireless Allows users to access the Internet from any location Next major challenge in networking: Widespread mobile high speed Internet access Current Mobile wireless technologies Slow access speeds compared to DSL,cable modem WLAN: Higher speed, but limited range and locations Wireless Application Protocol (WAP) Based on Wireless Application Environment (WAE) and Wireless Markup Language (WML) Streamlines HTTP and HTML for use in the very limited low speed and small screens of mobile devices Copyright 2005 John Wiley & Sons, Inc

Future Access Technologies
Passive Optical Networking (PON) Also called Fiber to the Home Potential of optical fiber communications to end users Possibility of thousands of channels (with WDM) Doesn’t require electricity, thus “passive” Limits its maximum distance (about 10 miles) No standards yet Ethernet to the Home Yipes.com is now doing this in several large US cities Gives home users 10BaseT or 100BaseT connections A TCP/IP router installed into the customer’s network connect to an Ethernet MAN No protocol conversion required Copyright 2005 John Wiley & Sons, Inc

Internet Governance No one operates the Internet Closest thing: Internet Society (ISOC) Open membership professional society Over 175 organizational and 8000 individual members in over 100 countries Mission: “Open development, evolution and use of the Internet for the benefit of the people in the world.” ISOC work areas Public policy: Involves in debates in copyright, censorship, privacy Education Training and education programs Standards Copyright 2005 John Wiley & Sons, Inc

ISOC Standard Bodies Internet Engineering Task Force (IETF) Concerned with evolution of Internet architecture and smooth operation of Internet Work through groups (organized by topics) Request For Comments (RFC): basis of Internet standards Internet Engineering Steering Group (IESG) Responsible for management of the standard process Establishes and administers rules in creating standards Internet Architecture Board (IAB) Provides strategic architectural oversight, guidance Internet Research Task Force (IRTF) Focus on long-term specific issues Copyright 2005 John Wiley & Sons, Inc

Internet 2 Many new projects designing new technologies to evolve Internet Primary North American projects Next Generation Internet (NGI) funded by NSF Developed very high performance Backbone Network Service (vBNS) Run by WorldCom University Corporation for Advanced Internet Development (UCAID) with 34 universities Developed Abilene network (also called Internet 2) Advanced Research and Development Network Operations Center (ARDNOC) funded by Canadian government Developed CA*Net Copyright 2005 John Wiley & Sons, Inc

Features of Future Internet
Access via Gigapops, similar to NAPs Operate at very high speeds (622 Mbps to 2.4 Gbps) using SONET, ATM and IPv6 protocols IPv6 not IPv4 New protocol development focuses on issues like Quality of Service Multicasting New applications include Tele-immersion Videoconferencing Copyright 2005 John Wiley & Sons, Inc

Concern about traffic slowing down Internet New fiber based circuits deployment  overbuilt Many new broadband technologies for high speed Internet access Simple to move large amount of data into most homes and business  richer multimedia apps Which access technology to dominate? Challenge: Figure out which one Copyright 2005 John Wiley & Sons, Inc

Prof. M. Ulema Manhattan College Computer Information Systems

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Prof. M. Ulema Manhattan College Computer Information Systems

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