Business Data Communications and Networking

Business Data Communications and Networking
Raymond R. Panko Copyright 2001 Prentice Hall Revision 1: August 2000

Basic Concepts and Principles
Chapter 1 Copyright 2000 Panko

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Part A: Business Data Communications and Networking
What’s in a Title?

Business For IS (information systems) students in business schools
Computer science and electrical engineering students are trained to work in hardware, software, and networking vendor firms, such as Microsoft, IBM, Oracle, and Cisco Systems IS graduates are trained to work in end user organizations, such as banks, government agencies, and manufacturing firms--organizations that use IT (information technology) to get their work done

Business The IS Job: Full life cycle support
To help firms understand how networking will help them work better To do needs analysis To plan and develop new networks To manage new networks after they are developed

Network A Network is an Any-to-Any Communication System
Can connect any station to any other Network

Network Each Station has a Unique Network Address “Connect to GHI”
To connect, only need to know the receiver’s address Like telephone number GHI DEF “Connect to GHI” ABC MNO JKL

Data Communications Originally, There was a Sharp Distinction:
Voice and Video Communication versus Data Communications, in which one or both parties is a computer Database Electronic mail World Wide Web Distinction is fading because voice and video communication are increasingly computer- based

Voice and Video Networks
Telephone Network Customer premises (home or office) Local loop (access line) connects customer premises to first switching office Switching Office Local Loop (Access Line) Connection Customer Premises Customer Premises

Hierarchy of switches Trunk lines connect switches Trunk Line Switch

Circuit End-to-End Connection between Phones May pass through multiple switches And trunk lines Circuit Circuit

Reserved Capacity Circuit capacity is reserved during duration of each call At each switch On each trunk line Reserved Capacity Reserved Capacity Circuit

Reserved Circuit Capacity Guarantees Throughput Never get less than reserved capacity Nothing like congestion on the Internet Reserved Circuit Capacity is Expensive Pay for it whether you use it or not Good for voice, because conversations are fairly constant Bad for data, because most data transmission is bursty; e.g., in World Wide Web, download, then stare at screen for a long time until next download

Packet-Switched Data Networks
Packet Switching Circuit switching is expensive due to reserved capacity Packet switching breaks transmissions into messages Messages are short (averaging a few hundred bytes) because switches handle short messages efficiently Messages are called packets (sometimes, frames or other names) Message Packets

Packet-Switched Data Networks
Switching Decision When a packet arrives at a switch, the switch must decide which of several ports (connections) to use to send the packet back out Complex Made at each switch B B? D? Switch A D Packet C? C

Packet Switched Data Networks
Multiplexing Packets from many conversations are mixed (multiplexed) over each trunk line Only pay for the capacity used Dramatic trunk line cost savings The reason for packet switching Multiplexing on Trunk Line

Part B: More Basic Concepts
Analog and Digital Communication Modems LANs and WANs

Analog Transmission In analog transmission, the state of the line can vary continuously, rising and falling smoothly in intensity among an infinite number of states State may be voltage, frequency or another line signal characteristic The human voice is like this When we speak into a telephone, we generate analogous (similar) electrical signals, hence the name New Strength Time

Digital Transmission In digital transmission, time is divided into periods of fixed length called clock cycles The line is kept constant (in one state) during each clock cycle so that the receiver can sample it anywhere during the cycle and get the same result New Strength Time Clock Cycle

Digital Transmission The line is kept in one of only a few possible states (conditions) during each clock cycle 2, 4, 8, 16, 32, rarely more There are fairly large differences between states If a signal is near one state but a bit off, the receiver will still read it correctly as being at that state New Strength Time Clock Cycle

Digital Transmission At the end of each clock cycle, the line may change abruptly to another of these few states Can also stay the same Abrupt Change Strength Stays Same Time Clock Cycle

Digital Versus Binary Transmission
Digital transmission: a few states (2, 4, 8, 16, etc.) Binary transmission: exactly two states One state represents 1, the other 0 Few States Two States 1 Digital Binary

Digital Communication
Modems Computers have digital output Telephone network assumes analog input Modem translates between digital device and analog line for data transmission over the phone system Analog Signal Digital Signal Modem

LANs and WANs Networks Have Different Geographical Scopes
Local Area Networks (LANs) Small Office Office Building Industrial Park / University Campus Wide Area Networks (WANs) Connect corporate sites or Connect corporate sites with sites of customers and suppliers

Elements of a Simple LAN
Hub or Switch Hub or Switch connects all stations Wiring is standard business telephone wiring (4 pairs in a bundle) Wiring

Client PC Client PCs are used by ordinary managers and professionals; receive service Servers provide services to client PCs Server Server Server Client PC

Client PC Begin with stand-alone PC Add a network interface card (NIC) to deal with the network Networks have many client PCs Server Most PC nets have multiple servers

Part C: Distributed Processing
Terminal-Host Systems File Server Program Access Client Server Processing

Terminal-Host Systems
Created in the 1960s Central host computer does all the processing Terminal is dumb--only a remote screen and keyboard Created in the 1960s, when microprocessors for terminal intelligence did not exist Terminals Host

Sizes Mainframes are the largest business hosts Optimized for business uses--file access speed is more crucial than mathematical processing

Many Mainframe Applications Were Created in the 1960s through 1980s Legacy systems--systems created by your predecessors Would not use the same platform today if built new But too expensive to rewrite all legacy applications at once Must live with many host legacy applications for now Older networks can be legacy systems as well; “legacy system” is not just limited to mainframe applications

PC Networks The Most Common Platform in Organizations
Allows PCs to share resources Both Wintel (Windows/Intel) PCs and Macintoshes Network

PC Network Components File Servers File Server
Store files (data files and programs) The most common type of server in PC networks Almost all file servers are themselves PCs File Server

File Server Program Access
File Server Program Access is the Most Common Way to Execute Programs in PC Networks Program files are stored on the file server before execution Stored on the File Server Client PC File Server

Program and data files are downloaded (copied) to the Client PC Executed on the client PC, not on the file server File server merely stores programs and data files Downloaded to Client PC, Executed There Client PC File Server

PC Processing Power Limits FSPA Programs Client PCs do not get very large Only programs small enough to operate on limited client PCs can be used Executed on the Client PC Client PC File Server

Client/Server Processing
Client and Server Machines Neither has to be a PC Platform independent Client Machine Server

C/S Servers often are Workstation Servers
Are computers more powerful (and expensive) than PCs Do not use standard Intel PC microprocessors Usually run the UNIX operating system Client and server workstations Confusingly, Windows NT client operating system is called Windows NT Workstation, where workstation is synonymous with “client”

Two Programs Client program on client machine Server program on server machine Work together to do the required processing Server Program Client Program Client Machine Server

Division of Labor Client program handles lighter work, such as user interface chores and light processing chores Server program handles heavy work, such as database retrieval Server Program Client Program Client Machine Server

Cooperation Through Message Exchange Client program sends Request message, such as a database retrieval request Server program sends a Response message to deliver the requested information or an explanation for failure Server Program Client Program Request Response Client Machine Server

Widely Used on the Internet For instance, webservice Client program (browser) sends an HTTP request asking for a webserver file Server program (webserver application program) sends an HTTP response message with the requested webpage HTTP Request Message HTTP Response Message

On the Internet, a Single Client Program--the Browser (also known as the client suite)--Works with Many Kinds of C/S server applications WWW, some , etc. Server Browser Webserver

Program Functionality (Size)
High program functionality requires large program size File Server Program Access Poor: client PCs are small, can only execute small programs Client/Server Processing Good: not limited to client PC processing power Heavy work can be done on the server machine Terminal-Host Systems Good: Hosts can be very large

Platform Independence
File Server Program Access Poor: Only works with PC clients and PC file servers Client/Server Processing Excellent: use any server you want, also any client Terminal-Host Systems Poor: Hosts require terminals and only work with a few terminal types

Scalability Ability to grow as demand grows File Server Program Access
Poor: client PCs do not get very large Client/Server Processing Very good: Platform independence allows servers to be larger than PCs To grow, leave client machine the same, increase the size of the server machine Terminal-Host Systems Excellent: have an enormous range of processing power

User Interface File Server Program Access Client/Server Processing
Very good: uses local PC processing power Client/Server Processing Very good: uses local PC processing power for user interface Terminal-Host System Poor: Relies on distant hosts; user interface quality limited by high long-distance transmission costs Monochrome, text-only screen; no animation

Response Time (When User Hits a Key)
File Server Program Access Very good: uses local PC processing power Client/Server Processing Very good: local PC processing power for user interface But retrievals from the server can cause delays Terminal-Host System Poor: Relies on distant hosts; long delays if overloaded

Part D: Accessing the World Wide Web from Home
Many students access the World Wide Web from home Here is how it works, in terms of standards

Accessing the WWW from Home
A Common and Important Situation Must be understood Good way of introducing networking concepts

The Internet The Internet is a Worldwide Group of Networks
Not a single network Individual networks on the Internet are called subnets

The Internet Messages are Broken into Small Packets for Transmission, as Noted Earlier More efficient than sending long messages Message Packets

The Internet Routers Connect the Internet’s individual networks (subnets) Cooperate to give an end-to-end route for each packet Routers Route

The Internet Hosts Any computer attached to the Internet is a host
Webservers are host Desktop and notebook PCs are hosts too Host Host

The Internet Network deliver messages based on network addresses
The Internet has two addressing systems for hosts IP addresses Host names Host Host

The Internet Host IP addresses Strings of 32 ones and zeros
Usually represented by four number segments separated by dots: dotted decimal notation For example, Official addresses for hosts

The Internet Dotted Decimal Notation
IP addresses are really strings of 32 bits (1s and 0s) To convert this to dotted decimal notation, first, divide them into four bytes (also called octets) Both octets and bytes are collections of eight bits

The Internet Dotted Decimal Notation
Convert each binary (Base 2) octet into decimal (Base 10) is 128 is 171 is 17 is 13

The Internet Binary 10100011 = Decimal 163 Note: Starts with 0
Position 7 Position Position (N) Value (2N) Bit Decimal Binary = Decimal 163 7 128 1 128 6 64 5 32 1 32 4 16 3 8 2 4 1 2 1 2 Note: Starts with 0 1 1 1 163

The Internet Why dotted decimal notation?
Strings of 32 bits are very difficult to memorize Dotted decimal representations of IP addresses are (somewhat) easier to remember So dotted decimal notation is merely a mnemonic device for representing IP addresses

CNN.COM The Internet Host Names
The other network addressing system on the Internet Easy to remember voyager.cba.hawaii.edu Two or more text “labels” separated by dots No relationship between segments and labels

CNN.COM The Internet Host Names Like nicknames Not official addresses
Each host must have an IP address But only some hosts have host names If you give it a host name, your browser must look up IP address of host (Chapter 2 discusses how) CNN.COM

The Internet Internet Service Providers (ISPs) Carrier Access Line
You must have an account with an ISP Connects you to the Internet May provide other services ( account, etc.) Carrier Access Line Usually provided by local telephone carrier Connects you to the ISP You pay for this separately from your ISP charges ISP Carrier Access Line

The Internet The Internet is Not Free
You pay your ISP around $20 per month, sometimes more Part of this pays for ISP expenses Part of this pays the Internet backbone to carry your messages You Usually Also Pay the Telephone Carrier Separately for the Carrier Access Line ISP Carrier Access Line

The Internet Some ISPs are “free” New
More correctly, they are advertiser supported You must see advertisements every time you use a free ISP ISP Carrier Access Line

The Internet Internet Backbone
Itself consists of many competing but interconnected backbone carriers Sometimes, backbone carriers are also ISPs Internet Backbone ISP ISP Carriers

The Internet ISPs Began in the United States
Is being copied and adopted by other countries However, not universal

Layered Standards Architectures
Part E: Standards Layered Standards Architectures TCP, IP, and TCP/IP Other Architectures

Standards Standards are rules of operation that most or all vendors follow Open standards are created and owned by public standards organizations No single vendor controls these standards

Standards Are Layered For Internet Access to a Webserver, standards are set at five layers Application Transport Internet Data Link Physical Together, these standards provide all that is needed for application programs on different hosts on different networks to work together

Internet Standards Messages are Exchanged at Multiple Layers App HTTP
Trans TCP Trans Int IP Int IP Int DL PPP DL ? DL Phy Modem Phy ? Phy User PC Router Webserver

Internet Standards Application Layer Standards
Standards at the application layer specify how two application programs communicate For example, browser on user PC and webserver application program on webserver Webserver Application Program Browser

Internet Standards HTTP (HyperText Transfer Protocol)
World Wide Web standard for browser-webserver application program exchanges Other applications ( , etc.) have different application standards Webserver Application Program Browser HTTP

Internet Standards Transport Layer Protocols PC or Other Computer PC
Standards at the transport layer specify how two host computers will work together, even if they are of different platform types (PCs, workstations, mainframes, and so forth) For instance, PC and non-PC webserver PC or Other Computer PC

Internet Standards The Transport Layer Gives Platform Independence
Two computers do not have to be of the same platform type A PC user does not even know what kind of computer the webserver is ? PC

Internet Standards HTTP Requires the Use of the TCP Transport Standard
Transmission Control Protocol TCP messages are called TCP segments TCP

Internet Standards Internet Layer Protocols
Standards at the internet layer specify how hosts and routers will act to route packets end to end, from the source host to the destination host, across many single networks (subnets) connected by routers Route Host Single Network (Subnet) Host

Internet Standards The Internet Protocol (IP) is the Main Protocol for Routing Packets Across the Internet The IP in “TCP/IP” IP messages are called packets All internet layer messages are called packets Packet IP

Internet Standards Subnets
Single networks (LANs, WANs, point-to-point link) on the Internet A packet will pass through several subnets along its route across the Internet Subnet Subnet Subnet

Point-to-Point Subnet
Internet Standards Different Subnets Can Have Different Subnet Protocols IP at the internet layer routes across different protocols at the subnet layer LAN Subnet Protocol 3 Point-to-Point Subnet Protocol 1 WAN Subnet Protocol 2

Subnets Standards Subnets are Single Networks on the Internet
Subnet Standards Divided into Two Layers Physical layer standards govern the transmission of individual bits within a subnet Data Link layer standards govern the transmission of messages within a subnet Organize individual bits into structured messages

Internet Standards Data Link Layer Standards
Standards at the data link layer specify how to transmit messages within a single network Messages at the data link layer are called frames Frame Data Link

Internet Standards Data Link Layer Standards
For accessing the Internet from home ... Point-to-Point Protocol (PPP) dominates Only used between home and ISP! Other subnets connecting routers are likely to use different subnet protocols! PPP ? ISP

Internet Standards Physical Layer Standards
While the data link layer is concerned with the organization and transmission of organized messages, standards at the physical layer specify how to transmit single bits one at a time Work bit by bit; no frame organization

Internet Standards Physical Layer Standards in Internet Access from Home Telephone jack (RJ11) Telephone wire Serial port connection to external modem Modem Serial Port External Modem Telephone Wire Wall Jack

Internet Standards Subnet Versus Internet Layer Standards
Internet layer provides routing across multiple subnets Subnet layer standards (data link and physical) provide for transmission within a single network Internet Layer Subnet Layer

Internet Standards Analogy for Subnet versus Internet Take a vacation
Route from beginning to end (like internet layer) For different parts, may travel by car, airplane, or boat (like subnet layer) Internet Layer Subnet Layer

Standards Organizations and Architectures
Architecture is a Design for Standards Creation Specifies what types of standards are needed (application, transport, etc.) After architecture is designed, individual standards of each type are created Analogy: architecture of house specifies what rooms will be needed and their relationships. After architecture is settled, individual rooms are designed

TCP/IP Standards Created by the Internet Engineering Task Force (IETF) Named after its two most widely known standards, TCP and IP TCP/IP is the architecture, while TCP and IP are individual standards However, these are not its only standards, even at the transport and internet layers IETF standards dominate in corporations at the application, transport, and internet layers However, application, transport, and internet standards from other architectures are still used

OSI Standards Reference Model of Open Systems Interconnection Created by the International Telecommunications Union-Telecommunications Standards Sector (ITU-T) And the International Organization for Standardization (ISO) OSI standards dominate the data link and physical layers Other architectures specify the use of OSI standards at these layers

Internet Standards 5-Layer Hybrid TCP/IP-OSI Architecture
Most widely used architecture in organizations today Used on the Internet Application TCP/IP Transport Internet Data Link OSI Physical

Internet Standards Recap: Accessing the WWW from Home App HTTP App
Trans TCP Trans Int IP Int IP Int DL PPP DL ? DL Phy Modem Phy ? Phy User PC Router Webserver

TCP/IP versus OSI Lowest Four Layers are Comparable in Functionality
Box Lowest Four Layers are Comparable in Functionality TCP/IP OSI Application Presentation Session Transport Internet Network Data Link (use OSI) Data Link Physical (use OSI) Physical

OSI Divides the Application Layer
Box OSI Session Layer Sets up a connection between two application programs on different machines Manage streams of transactions (session); if there is a break, can resume at the last roll-back point Transactions

Box OSI Presentation Layer Handles presentation differences between the two machines (how data are stored and represented) Two presentation layer processes select and use a common format for exchanging data Application Data Exchange in Common Format

Box OSI Application Layer Governs application-to-application communication freed from concerns about presentation format and transaction management

Quality of Service (QoS) Security
F. Tomorrow Quality of Service (QoS) Security

Quality of Service (QoS)
Throughput Problems and Guarantees Congestion When too many transmissions are on a network, traffic will slow down; this is congestion Latency Latency is the amount of time that packets or frames are delayed because of congestion. Measured in milliseconds (ms), Want guarantees of worst-case latency Throughput Throughput is the guaranteed speed in bits per second

Quality of Service (QoS)
Reliability Measures Availability Availability is the percentage of time the network is available to users. Telephone system has % availability Error Rate Error rate is the percentage of bits or messages that contain errors 3% - 6% of all packets are lost on the Internet

Security A Growing Problem Encryption for Confidentiality
Sender encrypts messages before sending them so that anyone intercepting them en route cannot read them Receiver can decrypt encrypted messages and read them Have confidentiality (unreadability by interceptors) New Encryption Decryption 47 101101 47

Security Authentication Access Control
Sender of a message must prove their identity To thwart impostors who impersonate people Access Control Prohibits or authorizes access to various resources (files, programs, etc.) Needs authentication but also more Access control lists for resources specify what resources the authorized person may use and how they may use them

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