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Local Area Networks Content Chapter 1: Introduction & Basic Principles

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1 Local Area Networks Content Chapter 1: Introduction & Basic Principles
Chapter 2: Topics in Data Communications Chapter 3: Protocols and the TCP/IP Suite Class 1

2 General Course Information
Instructor Info General & University Info Book & Course Material Course Schedule Grading & Exams Homework Spring 2005 Class 1: Introduction to LANs & WANs

3 Overview of LANs and MANs
The Need for Networking Driven by the decreasing cost of computer hardware and the dramatic increase in its capabilities Factors driving the creation of a new set of advanced desktop applications (with more on the way): Image Processing Speech Recognition Videoconferencing & Multimedia Three characteristics are of greatest use in classifying communication networks : Geographic Reach Topology Transmission Medium Spring 2005 Class 1: Introduction to LANs & WANs

4 LANs, MANs, and WANs Classification based on Geographic Reach
Characteristics of Wide Area Networks (WANs) Large Geographic Area Requires the crossing of public right-of-ways Partially or fully relies on common carrier circuits Slower speeds than LANs & MANs, although the spread of fiber optic facilities is beginning to change this Examples of WAN technologies: ISDN (BRI & PRI) SONET Frame Relay ATM Spring 2005 Class 1: Introduction to LANs & WANs

5 Class 1: Introduction to LANs & WANs
Comparison Spring 2005 Class 1: Introduction to LANs & WANs

6 LANs, MANs, and WANs Classification based on Geographic Reach
Characteristics of Local Area Networks (LANs) Small Geographic Area A LAN is completely owned and operated by a single organization The data rates of a LAN are usually an order of magnitude higher than a WAN Characteristics of Metropolitan Area Networks (MANs) Occupy the middle ground between LANs and WANs MANs typically adapt and extend LAN technologies to cover a larger geographic area Have provided greater bandwidth at lower costs within metropolitan areas Spring 2005 Class 1: Introduction to LANs & WANs

7 LANs, MANs, and WANs Applications
Personal Computer Local Networks Even with the proliferation of low cost PCs that allow staff members to do their own processing, there are still important reasons for networking these computer systems File and data sharing Share expensive network resources (printers, storage, etc.) Real-time and near real-time collaborative efforts Easy file and data protection (networked backups) Financially, the networking of low-cost PCs usually necessitates a low cost network technology Spring 2005 Class 1: Introduction to LANs & WANs

8 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

9 LANs, MANs, and WANs Applications
Back-end & Storage Area Networks (SANs) Used in large computer installations (e.g. mainframes) Key requirement is high-speed bulk data transfer between a small number of systems in a limited area Unlike traditional server-attached storage, SANs provide storage attached directly to the network (Increases efficiency) Key reasons for implementing a SAN Online backup systems Load leveling across multiple systems (storage ‘farms’) Wider accessibility of large amounts of data These requirements drive SANs to high bandwidth and high cost installations Spring 2005 Class 1: Introduction to LANs & WANs

10 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

11 LANs, MANs, and WANs Applications
High-Speed Office Networks Newer (particularly multimedia) applications are driving the development of higher speed LANs that are replacing the older PC Local Networks Use different technologies than SANs because they are meant to service a larger number of systems dispersed over a wider area Spring 2005 Class 1: Introduction to LANs & WANs

12 LANs, MANs, and WANs Applications
Backbone Local Networks Diverse requirements in typical organizations have led to the adoption of a multi-tiered LAN architecture Advantages of the multi-tiered LAN over the single-LAN architecture Greater reliability Greater capacity Lower overall cost The core of the multi-tiered LAN architecture is the backbone -- a high bandwidth network connecting together lower-speed, lower-cost LANs If the organization is geographically dispersed the backbone may be a MAN Spring 2005 Class 1: Introduction to LANs & WANs

13 LANs, MANs, and WANs Local Network Architecture
Information Distribution When setting requirements for a network installation, user traffic patterns must be explored What type of data will traverse the network? How is this data distributed? What is to be connected (PCs, servers, mainframes, all of the above, etc.)? As mentioned earlier, a multi-tiered network is typically the best approach to meeting organizational needs Typically a two or three tiered architecture is used Usually evolve in one of two ways, depending on how centralized the organization’s IT rules are: Bottom-up Top-down Spring 2005 Class 1: Introduction to LANs & WANs

14 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

15 LANs, MANs, and WANs LANs, WANs, and the Internet
Most organizations are geographically distributed & must deal with connecting together widely dispersed LANs Most organizations have two choices for WAN connectivity A private WAN A public network or the Internet Spring 2005 Class 1: Introduction to LANs & WANs

16 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

17 LANs, MANs, and WANs LANs, WANs, and the Internet
A private WAN Provides a dedicated connection from leased lines or a similar service Good for security & sites with high & predictable inter-site traffic Can be expensive, especially for smaller organizations & sites A public network or the Internet Provides an inexpensive & quick solution for connectivity Can also provide an access path for mobile workers Performance is an issue with real-time traffic or large data transfers Virtual private networks (VPN) used to address security: Encapsulation & tunneling are the key concepts IPsec is an example of a network layer VPN technology Spring 2005 Class 1: Introduction to LANs & WANs

18 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

19 Homework & Reading Assignment #1 -- due at class #3 (two weeks)!
Stallings Chapter 3: 3.3, 3.5, 3.8 Search on the Web for a manufacturer of Category 7 twisted pair cabling & document the following: Manufacturer Name Cable specs: attenuation, NEXT, FEXT paramters Basic description of the cable’s construction (a diagram helps) Is the cable sold as part of a structured cabling system? If so, give a brief description of what components are in the system Install the OPNet software and complete Lab0 (“Getting Started”). Answer the questions and also print out and submit the graphs you generate in the final section of the 2nd lesson (“Comparing Results”). Reading This Class: Stallings Chapters 1 through 3 Next Week: Chapters 4 through 6 Spring 2005 Class 1: Introduction to LANs & WANs

20 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

21 Chapter 2 – Topics in Data Communications
Class 1

22 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

23 Data Communications Concepts Introduction
Essential definitions for Data Communications Data, Signaling, & Transmission Systems Analog & Digital Data are entities that convey meaning, while signaling is the transfer of encoded data thru a transmission system Analog versus digital signaling Digital signaling usually less expensive than analog but care must be taken to properly engineer system (e.g. - attenuation) Combinations of analog & digital data and signals Analog data -> Analog signals Digital data -> Analog signals (Key equipment is a modem) Analog data -> Digital signals (Key equipment is a codec) Digital data -> Digital signals Digital systems suffer more attenuation than analog (proper engineering) Spring 2005 Class 1: Introduction to LANs & WANs

24 Class 1: Introduction to LANs & WANs
Data Communications Concepts Analog versus Digital Transmission Systems Analog systems transmit analog signals without regard for the content of the signal Amplifiers are used to boost the energy of the signal Amplifiers also boost the strength of any noise on the line, introducing the possibility that the signal could be lost Digital Transmission Systems are concerned with the content of the signal Repeaters used to regenerate the signal, overcoming attenuation Repeaters output a new copy cleansed of any noise, so noise is not cumulative (however, bit errors can still occur if the signal is not regenerated before it degrades too much) Spring 2005 Class 1: Introduction to LANs & WANs

25 Data Encoding Techniques Introduction
Encoding is the process of mapping digital data into the appropriate signal elements for transmission Encoding may be very complex or as simple as using binary signal elements (0s and 1s) Encoding schemes are chosen to assist the receiver in its two key tasks: Determining when the signal element begins and ends (so sampling is done at the proper time) Determining the value of the signal element (Is it a one? A zero?) Attenuation, data rate, & noise all play a role at receiver With analog data the encoding scheme also plays a key role in system performance but the details are a little different Spring 2005 Class 1: Introduction to LANs & WANs

26 Data Encoding Techniques Analog encoding of digital data
The basis for analog encoding is a base signal called the carrier signal Digital data is encoded (and decoded at the other end) by a device called a modem Three basic schemes for analog encoding of digital data: Amplitude Shift-keying (ASK) Frequency Shift-keying (FSK) Phase Shift-keying (PSK) These schemes can be combined for more sophisticated digital transmission systems that carry more data per signal element Spring 2005 Class 1: Introduction to LANs & WANs

27 Data Encoding Techniques Analog encoding of digital data
Amplitude-shift Keying Data represented by different amplitude levels of the carrier signal Simplest scheme, but inefficient and prone to noise Most valuable use is in optical systems Frequency-shift Keying Data represented by different frequency values near the carrier signal frequency Less prone to errors but requires more complex circuitry Phase-shift Keying Data represented by different phase shifts to the carrier frequency More efficient and noise resistant than ASK or FSK but requires more complex circuitry Spring 2005 Class 1: Introduction to LANs & WANs

28 Data Encoding Techniques Digital Encoding of Digital Data
The most common way to encode digital data is to use a binary signaling scheme consisting of two voltage levels NRZ-L (Non-Return to Zero Level) Each voltage level defines the value of the digital data Used only in very short connections NRZ-I (Non-Return to Zero Inverted) A transition at the beginning of a signal unit denotes a binary one This type of signaling is known as differential signaling; it is usually easier to detect a transition out of the background noise and the signals are polarity insensitive Clocking and DC current are usually problems Spring 2005 Class 1: Introduction to LANs & WANs

29 Data Encoding Techniques Digital Encoding of Digital Data
Manchester Encoding Example of a bi-phase coding; up to two signaling transitions per signal element (needs more bandwidth to transmit a given data rate) The mid-signal transition provides clocking as well as the data value (a zero data element is a high-to-low transition and a one is a low-to-high transition) Used in Ethernet LANs (IEEE 802.3) Differential Manchester Encoding Another bi-phase code The mid-signal transition provides clocking; the transition at the beginning of the signal element represents data (a zero data element has no transition at the beginning of a bit time while a one does) Used in Token Ring LANs (IEEE 802.5) Spring 2005 Class 1: Introduction to LANs & WANs

30 Data Encoding Techniques Digital Encoding of Analog Data
Pulse Code Modulation (PCM) is an example – used in the phone system to transmit analog data across digital networks Sampling rate based on the Nyquist theorem Digitized into 8 bit samples based on a nonlinear scale that provides good reproduction of the human voice Other digital-to-analog encoding schemes: Adaptive Differential Pulse Code Modulation (ADPCM) - used with voice transmission Delta Modulation - used rarely but also for voice transmission systems Code Excited Linear Prediction (CELP) - used in very low-bandwidth voice and multimedia communication systems Spring 2005 Class 1: Introduction to LANs & WANs

31 Multiplexing Introduction
Allows a transmission system to carry multiple independent signals simultaneously for higher efficiency Two general schemes are in use: FDM and TDM Frequency Division Multiplexing (FDM) Takes advantage of the fact that the useful bandwith of the transmission system exceeds the required bandwidth of a given signal Allows frequency spectrum to be divided & allocated to different signal sources Most commonly used with analog signaling and transmission Time Division Multiplexing (TDM) Spring 2005 Class 1: Introduction to LANs & WANs

32 Multiplexing Techniques
Allows a transmission system to carry multiple independent signals simultaneously for higher efficiency Two general schemes are in use: FDM and TDM Time Division Multiplexing (TDM) Takes advantage of the fact that the maximum bit rate of the system exceeds the required bit rate of the digital signal Each source is allocated a ‘time slot’ in the multiplexor Analog signals can be time division multiplexed, but it is very uncommon Two varieties of TDM: statistical and fixed time-slot Both FDM and TDM can be used in a synchronous or asynchronous manner Spring 2005 Class 1: Introduction to LANs & WANs

33 Transmission Media Introduction
The transmission media is the physical signal path between the transmitter and the receiver Can be guided (cables, waveguides, etc.) or unguided (open air) Our key concerns for transmission systems are data rate and distance Influencing factors: Bandwidth of the media Transmission impairments Interference Number of Receivers Spring 2005 Class 1: Introduction to LANs & WANs

34 Transmission Media (2) Twisted Pair Cable
Consists of a minimum of two copper wires twisted together and enclosed within a protective sheath Advantages: inexpensive, easy to work with, may already be installed where needed Disadvantages: limited in distance, data rate, and bandwidth; susceptible to interference Comes in two general varieties: shielded twisted pair (STP) and unshielded twisted pair (UTP) Shielding provides more noise immunity, especially at lower data rates STP costs more and is more difficult to work with Spring 2005 Class 1: Introduction to LANs & WANs

35 Transmission Media (3) Twisted Pair Cable
Category 3 and Category 5 UTP Rating standards devised by the Electronic Industries Association (EIA) The higher the category the better the cable; Cat 3 designed to support 10Mbps Ethernet while Cat 5 will support 100Mbps Ethernet The key difference between the two categories is the number of twists per unit length of cable Near-end Crosstalk (NEXT) is a key transmission impairment to minimize in any twisted pair cabling system While these are regarded as the most commonly found UTP installations, there are higher performance UTP choices Spring 2005 Class 1: Introduction to LANs & WANs

36 Transmission Media Twisted Pair Cable
High-performance Twisted Pair Category 5e (or enhanced Category 5): supports 125-MHz bandwidth on all four pairs, allowing Gigabit Ethernet to run over UTP up to 100 meters Category 6: supports over 200-MHz bandwidth on all four pairs; could potentially run high data rate ATM connections Category 7: will require special shielding and will likely support up to 700-MHz bandwidth on each pair Spring 2005 Class 1: Introduction to LANs & WANs

37 Transmission Media Coaxial Cable
Provides a two conductor transmission system where one conductor is situated inside the outer hollow conductor with an insulating dielectric in between Because of its structural characteristics coaxial cable is more resistant to noise than twisted pair Harder to work with and more expensive than twisted pair Coax systems can be grouped in three categories based on the type of signaling used: Baseband: digital signaling occupies the entire spectrum of the cable Broadband: carrier-band analog signaling is used, allowing multiple channels on the cable Carrierband: carrier-band analog signaling with low-end components; signal occupies entire spectrum of cable Spring 2005 Class 1: Introduction to LANs & WANs

38 Transmission Media Fiber Optic Cabling
A transmission system composed of a guided medium that allows the propagation of optical rays A range of fiber optic cabling exists for various needs, from ultra-pure fused silica (expensive but high data rate) to plastic (cheap with lower data rate for short runs) Advantages Huge bandwidth capacity Smaller size and lightweight Lower attenuation Electromagnetic isolation (high security & minimal interference) Common transmitters used are LEDs for (low-cost & low-speed systems) or Injection Laser Diodes (long-haul high-speed systems) Spring 2005 Class 1: Introduction to LANs & WANs

39 Transmission Media Fiber Optic Cabling
Basic fiber types Step-index multimode: cheapest to manufacture but allows light to travel different paths down the fiber, causing signal distortion & lowering the maximum data rate. Graded-index multimode: Higher grade of fiber with a varying refractive index that limits distortion of the signal. Singlemode: contains a core with a diameter close to the wavelength to be transmitted; allows only a single transmission path down the fiber which practically eliminates distortion Three wavelength ‘windows’ provide the best light propagation: 850, 1300, & 1550 nm Most multimode systems use the 850 nm window Long-haul transmission systems use the 1550 nm window because loss is lower at higher wavelengths Spring 2005 Class 1: Introduction to LANs & WANs

40 Transmission Media Unguided Media
Microwave Occupies the frequency spectrum from 1GHz to 30GHz; can provide either a highly directional or omni-directional system There are 3 main challenges to using microwave for data transmission: Frequency Allocation and licensing Interference Security Infrared Uses light in the infrared spectrum for data transmission Must be used line-of-sight or in an environment that allows infrared waves to be reflected Less issues associated with microwave but only for specialized uses Spring 2005 Class 1: Introduction to LANs & WANs

41 Data Communication Networks Introduction
For most WAN and MANs, transmission of data usually involves a number of intermediate switching nodes that move the data between source and destination The complete set of end nodes, data links, & intermediate switches is known as a communications network There is a spectrum of communication switching techniques; the two main variations are circuit and packet switching Spring 2005 Class 1: Introduction to LANs & WANs

42 Data Communication Networks Circuit Switching
Communication between end nodes is via a dedicated communications channel Communications via circuit switching involves three phases: Circuit establishment: the path is established before any data is transferred Data transfer Circuit disconnect: release of resource dedicated to the connection The fixed capacity of the channel is allocated for the duration of the connection; can be very inefficient with bursty traffic Circuit switching is best suited for synchronous data such as voice or real-time video Spring 2005 Class 1: Introduction to LANs & WANs

43 Data Communication Networks Packet Switching
Packet switching breaks data up into a series of packets, each appended with enough control information to ensure the packet transits the network successfully from source to destination Developed to address problems certain data sources have with circuit switching: Bursty data transmission Source and destination must operate at the same data rate Inefficient resource allocation Connection setup can be too slow for certain applications In addition to addressing the above problems, packet switching also has other benefits for data transmission: Under heavy load the network will accept packets but delay increases Priorities for transmission of the packets can be set Spring 2005 Class 1: Introduction to LANs & WANs

44 Data Communication Networks Packet Switching
Two main varieties: datagrams or virtual circuits Datagram Approach: Each packet is routed independently of all others, leading to the following consequences: Packets don’t take the same routes, may arrive out of sequence No circuit setup time, so data flow begins without delay Data can easily flow around problems in the network Virtual Circuit Approach: a preplanned route through the network is established before any data is sent Requires circuit setup and teardown but routes along the connection are shared with other packets A routing decision does not have to be made for every packet May provide enhanced services such as error & flow control, and packet sequencing not available in a datagram environment Spring 2005 Class 1: Introduction to LANs & WANs

45 Data Communication Networks Hybrids
Multi-rate Circuit Switching Extends circuit switching to allow one or more fundamental channels to be bundled together to provide a range of data connection rates Examples of multi-rate switching are ISDN and inverse multiplexing Frame Relay WAN service based on a connection-oriented packet data protocol Frame Relay evolved from X.25; the new protocol was streamlined by eliminating features necessary on earlier, less reliable X.25 data communications networks Cell Relay (ATM) A further evolution of connection-oriented packet data services Unlike frame relay fixed length data units (cells) are used which allow high-speed hardware based switching Spring 2005 Class 1: Introduction to LANs & WANs

46 Class 1: Introduction to LANs & WANs
Comparison Packet Switching vs. Circuit Switching Is packet switching a “clear winner?” Great for bursty data Resource sharing No call setup Excessive congestion: packet delay and loss Protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? Bandwidth guarantees needed for audio/video apps Still an unsolved problem Spring 2005 Class 1: Introduction to LANs & WANs

47 Class 1: Introduction to LANs & WANs
Routing Routing in Packet-Switched Networks Goal: move packets among routers from source to destination We’ll study several path selection algorithms (chapter 5) Datagram network: Destination address determines next hop Routes may change during session Analogy: postal service Virtual circuit network: Each packet carries tag (virtual circuit ID), tag determines next hop Fixed path determined at call setup time, remains fixed through call Routers maintain per-call state Spring 2005 Class 1: Introduction to LANs & WANs

48 Class 1: Introduction to LANs & WANs
Taxonomy Telecommunication networks Circuit-switched networks Packet-switched networks Datagram networks VC Based networks TDM FDM Spring 2005 Class 1: Introduction to LANs & WANs

49 Class 1: Introduction to LANs & WANs
Network Access End hosts are connected to edge routers through access networks Types of access networks: Residential access Company access Mobile access Types of physical media technologies for access networks: Fiber Coaxial cable Twisted-pair telephone wire Radio spectrum Spring 2005 Class 1: Introduction to LANs & WANs

50 Class 1: Introduction to LANs & WANs
Access Network Access Network: Residential Access Connects home end systems to the network edge Typically, through an ISP End hosts are PCs AKA last mile Means of residential access: dialup, DSL, Cable, etc. Dial-up modem Uses POTS line  twisted pair copper wire Calls ISP’s number Max. data rate: 56 Kbps Phone line is tied up when connected to ISP Digital Subscriber Line (DSL) Does not tie up the phone line Uses existing twisted-pair line Asymmetric upstream and downstream data rates Downstream: 384 Kb/s—1.5 Mb/s Upstream: 128—256 Kb/s Hybrid Fiber Coaxial (HFC) Cable Utilizes distribution network of video broadcast cable Cable modem uses two channels for data transmission Shared among subscribers 10 Base-T Ethernet port Spring 2005 Class 1: Introduction to LANs & WANs

51 Class 1: Introduction to LANs & WANs
LAN access LAN access Company/university local area network (LAN) connects end system to edge router Ethernet: Shared or dedicated cable connects end system and router 10 Mbs, 100Mbps, Gigabit Ethernet Deployment: institutions, home LANs soon LANs: Link layer (chapter 5) Wireless Access Networks Shared wireless access network connects mobile end system to router at a base station Laptops, PDAs, etc. Wireless LANs: Radio spectrum replaces wire Wireless LANs are based on IEEE b standard (11 Mbps) Wider-area wireless access CDPD (Cellular Digital Packet Data): wireless access to ISP router via cellular network Third Generation (3G) wireless: packet-switched wide-area Internet access at 384 Kbps Spring 2005 Class 1: Introduction to LANs & WANs

52 Class 1: Introduction to LANs & WANs
Example 1 How long will it take to send a file of 640,000 bits from host A to host B over a circuit-switched network. Suppose all links in the network are TDM with: 24 slots and have a bit rate of 1.536Mbps It takes 500 msec to establish an end-to-end circuit before host A begins transmitting to B How long will it take to send file? Spring 2005 Class 1: Introduction to LANs & WANs

53 Class 1: Introduction to LANs & WANs
Example 1 How long will it take to send a file of 640,000 bits from host A to host B over a circuit-switched network. Suppose all links in the network are TDM with: 24 slots and have a bit rate of 1.536Mbps It takes 500 msec to establish an end-to-end circuit before host A begins transmitting to B How long will it take to send file? Transmission rate for each circuit = Mbps / 24 = 64 Kbps Time to send 640 Kbits file = ( bits)/(64 Kbits/sec) = 10 seconds Including circuit setup overhead, time to send file is 10.5 seconds This calculation is independent of the # of end-to-end links and does not include propagation delays Spring 2005 Class 1: Introduction to LANs & WANs

54 Class 1: Introduction to LANs & WANs
Example 2 Packet Switching: Two forwarding mechanisms: No segmentation  message switching With segmentationpipelining Example: 7.5 million bits message sent over 3 links, each of 1.5 Mbps Time required without segmentation = (7.5/1.5)x3=15 sec Now segment packet into 5000 chunks each of 1500 bits Time for whole packet = sec Pipelining results in reduction of delays as all links are being utilized simultaneously Spring 2005 Class 1: Introduction to LANs & WANs

55 Delay in Packet-Switched networks
Transmission delay: R=link bandwidth (bps) L=packet length (bits) Time to send bits into link = L/R Propagation delay: d = length of physical link s = propagation speed in medium (~2x108 m/sec) Propagation delay = d/s Spring 2005 Class 1: Introduction to LANs & WANs

56 Class 1: Introduction to LANs & WANs
Example 3 Packet Switching Calculation of delay: A packet of L bits Q links between source and destination hosts Each link has a data rate of R bits/sec Assume: No queuing delays No end-to-end propagation delays No connection establishment is required How long it takes to send this L bit packet from source to destination? Time to traverse the first link from source host: L/R seconds Q-1 more such links are traversed before reaching destination Thus, total delay: QL/R seconds  more delay for larger packets Spring 2005 Class 1: Introduction to LANs & WANs

57 Chapter 3 – Protocols & the TCP/IP Suite
Class 1

58 Protocols & the TCP/IP Suite The Need for a Protocol Architecture
Communication between a set of networked systems can involve a very complex set of procedures Example tasks for file transfer: Communication link setup Ensure the receiver is ready to accept data Make sure the file management application at the receiver is prepared to receive and store the file Do file translation if necessary Confirm delivery & check for errors Networking protocols use the concept of modularity well known in the software development arena Spring 2005 Class 1: Introduction to LANs & WANs

59 Protocols & the TCP/IP Suite The Need for a Protocol Architecture
In Networking protocol architectures, the modules are arranged in a vertical stack Each layer performs a distinct & essential set of tasks; more ‘primitive’ tasks are usually found in lower layers (‘closer’ to the transmission medium) Layers should be defined so changes in one layer do not necessitate changes in the other layers It takes at least two systems to communicate across a network and each of these systems need the same layers The peer layers on each system communicate with each other; the set of rules governing it is known as a protocol Syntax Semantics Timing Spring 2005 Class 1: Introduction to LANs & WANs

60 Protocols & the TCP/IP Suite The TCP/IP Protocol Architecture
The TCP/IP protocol suite is a large collection of public standards approved by the IAB (IETF) and used as the foundation for the Internet and similar private networks Communication across a network using TCP/IP protocols involves two general steps: Getting the data across the network to the destination systems Getting the data within the destination system to the right application Because of layering & the general steps above, the TCP/IP protocol suite was designed with five layers (lowest to highest): Physical Layer: the physical interface between the network and the attached system; covers the nature of the data signals, characteristics of the transmission medium, the data rate, etc. Spring 2005 Class 1: Introduction to LANs & WANs

61 Protocols & the TCP/IP Suite The TCP/IP Layers
Network Access Layer: specifies how data is exchanged between the attached system and the network; will include addressing, framing, and other features such as prioritization Details of this layer depends on the physical layer; separating this layer from higher layer functions allows higher layers to be used over a wide range of network technologies Concerned with delivering data across a single network only Internet Layer: specifies how data can be routed across multiple networks All devices across an internet must share a common internetworking layer to relay the data Routers are the devices responsible for relaying data in an internet A global address space is an essential feature of this layer Spring 2005 Class 1: Introduction to LANs & WANs

62 Protocols & the TCP/IP Suite The TCP/IP Layers
Transport Layer: specifies a set of end-to-end services usually common to a number of applications communicating across an internet (error-free, sequenced data delivery, etc.) Currently there are two transport layer specifications in the TCP/IP suite: the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP) TCP provides a reliable connection-oriented transport service UDP provides a low overhead transport service with no payload error checking, flow control, or sequencing Application Layer: specifies the functionality of the application itself (file transfer, remote terminal access, etc.) Spring 2005 Class 1: Introduction to LANs & WANs

63 Protocols & the TCP/IP Suite The Operation of TCP & IP
For successful communication across an internet, each system must have at least one globally unique address Also, each host process needs a locally unique address An example TCP/IP based data transfer [Figure 3.1] Spring 2005 Class 1: Introduction to LANs & WANs

64 Protocols & the TCP/IP Suite The Operation of TCP & IP
The key to operation of the protocol stack is encapsulation Spring 2005 Class 1: Introduction to LANs & WANs

65 Protocols & the TCP/IP Suite Examples of TCP/IP Applications
Electronic Mail relies on the Simple Mail Transfer Protocol (SMTP) – this covers the addressing and delivery of messages; other standards cover message format File Transfer functionality relies on the File Transfer Protocol (FTP), which provides an authenticated means for accessing and transferring files to and from a remote system Remote Terminal Access functionality relies on the TELNET protocol; it emulates a variety a hardwired terminals over a network connection Other important TCP/IP Applications include the World Wide Web (HTTP or the Hypertext Transfer Protocol), Network News (NNTP or the Network News Transfer Protocol), and Directory Services (LDAP or the Lightweight Directory Access Protocol) Spring 2005 Class 1: Introduction to LANs & WANs

66 Protocols & the TCP/IP Suite The OSI Protocol Architecture
The ISO (an international standards body) has also developed a network protocol reference standard called the OSI model While useful to know and important in the context of some international networks, the OSI model has not flourished for two primary reasons: The TCP/IP have matured and equipment using these protocols were widely adopted before the OSI model was finished The OSI model and standards developed using it tend to be very complex, making them harder to implement and operate Spring 2005 Class 1: Introduction to LANs & WANs

67 Protocols & the TCP/IP Suite The OSI Protocol Architecture
The OSI model consists of seven layers (from bottom up): Physical: concerned with the transmission and signaling across the physical media (same as TCP/IP model) Data Link: provides reliable transfer on a physical link by formatting data in frames; providing timing, error, & flow control Network: provides a universal switching/routing layer to insulate upper layers from differing data link & physical layers Transport: provides reliable, transparent end-to-end delivery of data; may also provide end-to-end error recovery & flow control Session: establishes, manages, and terminates connections between communicating applications Presentation: specifies how data should be represented between communicating applications Application: provides user access to networked resources through a specific functional program Spring 2005 Class 1: Introduction to LANs & WANs

68 Protocols & the TCP/IP Suite Internetworking
It is very common for an organization to have different varieties of LANs as well as geographically dispersed networks A quick review of Internetworking Terms Communication Network Internet (internet) Intranet End System Intermediate System Bridge Router Spring 2005 Class 1: Introduction to LANs & WANs

69 Protocols & the TCP/IP Suite Routers
Routers are key pieces of equipment that allow internetworking across dissimilar networks Essential functions for a router: Provide links between physically distinct (and heterogeneous) networks Decide when and where to forward packets to attached networks Provide these functions in such a way that no modifications are required to the attached networks Networking issues routers must deal with: Layer 2 Addressing Schemes Maximum Packet sizes Interfaces Reliability Spring 2005 Class 1: Introduction to LANs & WANs

70 Protocols & the TCP/IP Suite An Internetworking Example [Figure 3.5]
Spring 2005 Class 1: Introduction to LANs & WANs

71 Protocols & the TCP/IP Suite Appendix: IP, TCP, and UDP
IP version 4 (IPv4) The current version of the network layer protocol used in the Internet IPv4 header fields: Spring 2005 Class 1: Introduction to LANs & WANs

72 Protocols & the TCP/IP Suite Appendix: IP version 6 (IPv6)
Next generation version promises a number of improvements: HUGE address space, with support for a many addressing schemes Different header structure and options to speed processing Built-in Quality of Service and security functionality IPv6 Header fields: Spring 2005 Class 1: Introduction to LANs & WANs

73 Class 1: Introduction to LANs & WANs
Protocols & the TCP/IP Suite Appendix: the Transmission Control Protocol (TCP) Provides a sophisticated connection-oriented transport service to networked applications on an IP network TCP provides reliable and sequenced streaming delivery of application-layer data TCP Header fields: Spring 2005 Class 1: Introduction to LANs & WANs

74 Class 1: Introduction to LANs & WANs
Protocols & the TCP/IP Suite Appendix: the User Datagram Protocol (UDP) Provides a basic low-overhead connectionless transport service to networked applications on an IP network UDP provides unreliable delivery of application-layer data in which delivery or duplication of data is not guaranteed UDP is good for applications that provide their own enhanced delivery services as well as multicast and streaming applications UDP Header fields: Spring 2005 Class 1: Introduction to LANs & WANs

75 Homework & Reading Assignment #1 -- due at class #3 (two weeks)!
Stallings Chapter 3: 3.3, 3.5, 3.8 Search on the Web for a manufacturer of Category 7 twisted pair cabling & document the following: Manufacturer Name Cable specs: attenuation, NEXT, FEXT paramters Basic description of the cable’s construction (a diagram helps) Is the cable sold as part of a structured cabling system? If so, give a brief description of what components are in the system Install the OPNet software and complete Lab0 (“Getting Started”). Answer the questions and also print out and submit the graphs you generate in the final section of the 2nd lesson (“Comparing Results”). Reading This Class: Stallings Chapters 1 through 3 Next Week: Chapters 4 through 6 Spring 2005 Class 1: Introduction to LANs & WANs

76 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

77 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

78 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

79 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

80 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

81 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

82 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

83 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

84 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

85 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

86 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

87 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

88 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

89 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

90 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

91 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

92 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

93 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

94 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

95 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

96 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

97 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

98 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

99 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

100 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

101 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

102 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

103 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

104 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

105 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

106 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

107 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs

108 Class 1: Introduction to LANs & WANs
Spring 2005 Class 1: Introduction to LANs & WANs


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