Data Transmission, MediaSignal Encoding TechniquesData Communication TechniquesData Link Control, ATMComputer Communication NetworksIntroductory LectureMultiplexing, Switching, RoutingSpread Spectrum, Wireless NetworksLocal and Wide Area Networks

Course OverviewData Communication Networks and Open System StandardsData TransmissionData Link ControlsTechnologies of Local Area Networks and Wide Area NetworksCommunication Architecture and Protocols

Course ObjectivesThe aim of this course is to provide a unified overview in the basic principles of data communications and computer networks. The lectures emphasize basic principles and topics of fundamental importance concerning the technology and architecture of this field, as well as providing the state of the art topics.

Course ObjectivesFollowings are the basic objectives :To provide a conceptual foundation for the study of data communications using the Open Systems Interconnect (OSI) model for layered architecture To develop an understanding in basic hardware and software environments for data communications and computer networks

Text BooksData and Computer Communications, 7th Edition, Prentice Hall, 2004

by William Stallings

Data Communication and Networking, 3rd Edition, McGraw-Hill, 2004

by Behrouz A. Forouzan

Course Websitehttp://web.uettaxila.edu.pk/cms/teCCNmsAU09/

Class Schedule [Tuesdays 4~6 / 6~9]

No.Lecture TopicsText's slides1Course Orientation, Overviewchapter 1, chapter 22Data Transmission, Mediachapter 3, chapter 43Signal Encoding Techniqueschapter 54Data Communication Techniqueschapter 65Data Link Controlchapter 76Multiplexingchapter 87Spread Spectrumchapter 98Circuit and Packet Switching, ATMchapter 109Routing/Congestion Control in Switched Networkschapter 12, chapter 1310Cellular Wireless Networkschapter 1411LANschapter 1512High Speed LANschapter 1613Class Summary

Overview

Simplified Communications ModelSourceGenerates data to be transmittedTransmitterConverts data into transmittable signalsTransmission SystemCarries dataReceiverConverts received signal into dataDestinationTakes incoming data

Simplified Communications Model - Diagram

Simplified Data Communications Model

NetworkingPoint to point communication not usually practicalDevices are too far apartLarge set of devices would need impractical number of connectionsSolution is a communications networkWide Area Network (WAN)Local Area Network (LAN)

AB

Connecting N users: Directly ...Bus: broadcast, collisions, media access controlFull mesh: Cost vs simplicity

. . .Full meshBus Address concept needed if we want the receiver alone to consume the packet!

Connecting N users: IndirectlyStar: One-hop path to any node, reliability, forwarding functionSwitch S can filter and forward!Switch may forward multiple packets in parallel for additional efficiency!

StarS

Connecting N users: Indirectly Ring: Reliability to link failure, near-minimal links All nodes do forwarding and filtering

Ring

Topologies: Indirect Connectivity

RingStarSTree

Inter-Networks: Networks of Networks=InternetOur goal is to design this black box on the right

Wide Area NetworksLarge geographical areaCrossing public rights of wayRely in part on common carrier circuitsAlternative technologiesCircuit switchingPacket switchingFrame relayAsynchronous Transfer Mode (ATM)

Circuit SwitchingDedicated communications path established for the duration of the conversatione.g. telephone network

Packet SwitchingData sent out of sequenceSmall chunks (packets) of data at a timePackets passed from node to node between source and destinationUsed for terminal to computer and computer to computer communications

Frame RelayPacket switching systems have large overheads to compensate for errorsModern systems are more reliableErrors can be caught in end systemMost overhead for error control is stripped out

Asynchronous Transfer ModeATMEvolution of frame relayLittle overhead for error controlFixed packet (called cell) lengthAnything from 10Mbps to many GbpsConstant data rate using packet switching technique

Local Area NetworksSmaller scopeBuilding or small campusUsually owned by same organization as attached devicesData rates much higherUsually broadcast systemsNow some switched systems and ATM are being introduced

LAN ConfigurationsSwitchedSwitched Ethernet

May be single or multiple switchesATM LANFibre ChannelWirelessMobilityEase of installation

Metropolitan Area NetworksMANMiddle ground between LAN and WANPrivate or public networkHigh speedLarge area

NetworkingConfiguration

Further ReadingStallings, W. [2003] Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, Chapter 1Web site for Stallings bookhttp://williamstallings.com/DCC7e.html

Protocols and Architecture

Need For Protocol ArchitectureE.g. File transferSource must initiate communications. Find Path or inform network of destinationSource must check destination is prepared to receiveFile transfer application on source must check destination file management system will accept and store file for his userMay need file format translationTask broken into subtasksImplemented separately in layers in stackFunctions needed in both systemsPeer layers communicate

Key Elements of a ProtocolSyntaxData formatsSignal levelsSemanticsControl informationError handlingTimingSpeed matchingSequencing

Protocol ArchitectureTask of communication broken up into modulesFor example file transfer could use three modulesFile transfer applicationCommunication service moduleNetwork access module

Simplified File Transfer Architecture

A Three Layer ModelNetwork Access LayerTransport LayerApplication Layer

Network Access LayerExchange of data between the computer and the networkSending computer provides address of destinationMay invoke levels of serviceDependent on type of network used (LAN, packet switched etc.)

Transport LayerReliable data exchangeIndependent of network being usedIndependent of application

Application LayerSupport for different user applicationse.g. e-mail, file transfer

Protocol Architectures and Networks

Addressing RequirementsTwo levels of addressing requiredEach computer needs unique network addressEach application on a (multi-tasking) computer needs a unique address within the computerThe service access point or SAPThe port on TCP/IP stacks

Protocols in Simplified Architecture

Protocol Data Units (PDU)At each layer, protocols are used to communicateControl information is added to user data at each layerTransport layer may fragment user dataEach fragment has a transport header addedDestination SAPSequence numberError detection codeThis gives a transport protocol data unit

Protocol Data Units

Network PDUAdds network headernetwork address for destination computerFacilities requests

Operation of a Protocol Architecture

Standardized Protocol ArchitecturesRequired for devices to communicateVendors have more marketable productsCustomers can insist on standards based equipmentTwo standards:OSI Reference model

Never lived up to early promisesTCP/IP protocol suite

Most widely usedAlso: IBM Systems Network Architecture (SNA)

OSIOpen Systems InterconnectionDeveloped by the International Organization for Standardization (ISO)Seven layersA theoretical system delivered too late!TCP/IP is the de facto standard

OSI - The ModelA layer modelEach layer performs a subset of the required communication functionsEach layer relies on the next lower layer to perform more primitive functionsEach layer provides services to the next higher layerChanges in one layer should not require changes in other layers

OSI Layers

The OSI Environment

OSI as Framework for Standardization

Layer Specific Standards

Elements of StandardizationProtocol specificationOperates between the same layer on two systemsMay involve different operating systemProtocol specification must be precise

Format of data unitsSemantics of all fieldsallowable sequence of PDUsService definitionFunctional description of what is providedAddressingReferenced by SAPs

Service Primitives and ParametersServices between adjacent layers expressed in terms of primitives and parametersPrimitives specify function to be performedParameters pass data and control info

Primitive Types

REQUEST A primitive issued by a service user to invoke some service and to pass the parameters needed to specify fully the requested service INDICATION A primitive issued by a service provider either to: indicate that a procedure has been invoked by the peer service user on the connection and to provide the associated parameters, or notify the service user of a provider-initiated action RESPONSE A primitive issued by a service user to acknowledge or complete some procedure previously invoked by an indication to that user CONFIRM A primitive issued by a service provider to acknowledge or complete some procedure previously invoked by a request by the service user

Timing Sequence for Service Primitives

OSI Layers (1)PhysicalPhysical interface between devices

MechanicalElectricalFunctionalProceduralData LinkMeans of activating, maintaining and deactivating a reliable linkError detection and controlHigher layers may assume error free transmission

OSI Layers (2)NetworkTransport of informationHigher layers do not need to know about underlying technologyNot needed on direct linksTransportExchange of data between end systemsError freeIn sequenceNo lossesNo duplicatesQuality of service

OSI Layers (3)SessionControl of dialogues between applicationsDialogue disciplineGroupingRecoveryPresentationData formats and codingData compressionEncryptionApplicationMeans for applications to access OSI environment

Use of a Relay

TCP/IP Protocol ArchitectureDeveloped by the US Defense Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)Used by the global InternetNo official model but a working one.Application layerHost to host or transport layerInternet layerNetwork access layerPhysical layer

Physical LayerPhysical interface between data transmission device (e.g. computer) and transmission medium or networkCharacteristics of transmission mediumSignal levelsData ratesetc.

Network Access LayerExchange of data between end system and networkDestination address provisionInvoking services like priority

Internet Layer (IP)Systems may be attached to different networksRouting functions across multiple networksImplemented in end systems and routers

Transport Layer (TCP)Reliable delivery of dataOrdering of delivery

Application LayerSupport for user applicationse.g. http, SMTP

OSI v TCP/IP

TCPUsual transport layer is Transmission Control ProtocolReliable connectionConnectionTemporary logical association between entities in different systemsTCP PDU Called TCP segmentIncludes source and destination port (c.f. SAP)

Identify respective users (applications)Connection refers to pair of portsTCP tracks segments between entities on each connection

UDPAlternative to TCP is User Datagram ProtocolNot guaranteed deliveryNo preservation of sequenceNo protection against duplicationMinimum overheadAdds port addressing to IP

TCP/IP Concepts

Addressing levelLevel in architecture at which entity is namedUnique address for each end system (computer) and routerNetwork level address IP or internet address (TCP/IP)Network service access point or NSAP (OSI)Process within the systemPort number (TCP/IP)Service access point or SAP (OSI)

Trace of Simple OperationProcess associated with port 1 in host A sends message to port 2 in host BProcess at A hands down message to TCP to send to port 2TCP hands down to IP to send to host BIP hands down to network layer (e.g. Ethernet) to send to router JGenerates a set of encapsulated PDUs

PDUs in TCP/IP

Example Header InformationDestination portSequence numberChecksum

Some Protocols in TCP/IP Suite

Required ReadingStallings, W. [2003] Data and Computer Communications (7th edition), Prentice Hall, Upper Saddle River NJ, Chapter 2Web site for Stallings bookhttp://williamstallings.com/DCC7e.htmlRFCs from Internet

Q&A?