Data and Computer Data and Computer CommunicationsCommunications

Presentation by Presentation by

Ihab AliIhab AliOriginal slides by Lawrie BrownOriginal slides by Lawrie Brown

Lecture #1Lecture #1

Data Communications, Data Data Communications, Data Networks, and the InternetNetworks, and the Internet

The fundamental problem of The fundamental problem of communication is that of reproducing at communication is that of reproducing at one point either exactly or approximately a one point either exactly or approximately a message selected at another point message selected at another point - - The The Mathematical Theory of CommunicationMathematical Theory of Communication, , Claude ShannonClaude Shannon

Communications TasksCommunications Tasks

Transmission system utilization Addressing

Interfacing Routing

Signal generation Recovery

Synchronization Message formatting

Exchange management Security

Error detection and correction Network management

Flow control

Data Communications ModelData Communications Model

Need For Need For ProtocolProtocol ArchitectureArchitecture

data exchange can involve complex data exchange can involve complex procedures, cf. file transfer exampleprocedures, cf. file transfer example

better if task broken into subtasksbetter if task broken into subtasks implemented separately in layers in stackimplemented separately in layers in stack

each layer provides functions needed to each layer provides functions needed to perform comms for layers aboveperform comms for layers above

using functions provided by layers belowusing functions provided by layers below peer layers communicate with a protocolpeer layers communicate with a protocol

TCP/IP Protocol ArchitectureTCP/IP Protocol Architecture

developed by US Defense Advanced developed by US Defense Advanced Research Project Agency (DARPA) Research Project Agency (DARPA)

for ARPANET packet switched networkfor ARPANET packet switched network used by the global Internetused by the global Internet protocol suite comprises a large collection protocol suite comprises a large collection

of standardized protocolsof standardized protocols

Simplified Network Simplified Network ArchitectureArchitecture

TCP/IP LayersTCP/IP Layers

no official model but a working one no official model but a working one Application layerApplication layer Host-to-host, or transport layerHost-to-host, or transport layer Internet layerInternet layer Network access layerNetwork access layer Physical layerPhysical layer

Physical LayerPhysical Layer

concerned with physical interface between concerned with physical interface between computer and networkcomputer and network

concerned with issues like:concerned with issues like: characteristics of transmission mediumcharacteristics of transmission medium signal levelssignal levels data ratesdata rates other related mattersother related matters

Network Access LayerNetwork Access Layer

exchange of data between an end system exchange of data between an end system and attached networkand attached network

concerned with issues like :concerned with issues like : destination address provisiondestination address provision invoking specific services like priorityinvoking specific services like priority access to & routing data across a network link access to & routing data across a network link

between two attached systemsbetween two attached systems allows layers above to ignore link specificsallows layers above to ignore link specifics

Internet Layer (IP)Internet Layer (IP)

routing functions across multiple networksrouting functions across multiple networks for systems attached to different networksfor systems attached to different networks using IP protocolusing IP protocol implemented in end systems and routersimplemented in end systems and routers routers connect two networks and relays routers connect two networks and relays

data between themdata between them

Transmission MediumTransmission Medium

selection is a basic choiceselection is a basic choice internal use entirely up to businessinternal use entirely up to business long-distance links made by carrierlong-distance links made by carrier

rapid technology advances change mixrapid technology advances change mix fiber opticfiber optic wirelesswireless

transmission costs still hightransmission costs still high hence interest in efficiency improvementshence interest in efficiency improvements

NetworkingNetworking

growth of number & power of computers is growth of number & power of computers is driving need for interconnectiondriving need for interconnection

also seeing rapid integration of voice, also seeing rapid integration of voice, data, image & video technologiesdata, image & video technologies

two broad categories of communications two broad categories of communications networks:networks: Local Area Network (LAN)Local Area Network (LAN) Wide Area Network (WAN)Wide Area Network (WAN)

Wide Area NetworksWide Area Networks

span a large geographical areaspan a large geographical area cross public rights of waycross public rights of way rely in part on common carrier circuitsrely in part on common carrier circuits alternative technologies used include:alternative technologies used include:

circuit switchingcircuit switching packet switchingpacket switching frame relayframe relay Asynchronous Transfer Mode (ATM)Asynchronous Transfer Mode (ATM)

Local Area NetworksLocal Area Networks

smaller scopesmaller scope Building or small campusBuilding or small campus

usually owned by same organization as usually owned by same organization as attached devicesattached devices

data rates much higherdata rates much higher switched LANs, eg Ethernetswitched LANs, eg Ethernet wireless LANswireless LANs

The InternetThe Internet

Internet evolved from ARPANETInternet evolved from ARPANET first operational packet networkfirst operational packet network applied to tactical radio & satellite nets alsoapplied to tactical radio & satellite nets also had a need for interoperabilityhad a need for interoperability led to standardized TCP/IP protocolsled to standardized TCP/IP protocols

Internet ElementsInternet Elements

Internet ArchitectureInternet Architecture

Example ConfigurationExample Configuration

Transport Layer (TCP)Transport Layer (TCP)

common layer shared by all applicationscommon layer shared by all applications provides reliable delivery of dataprovides reliable delivery of data in same order as sentin same order as sent commonly uses TCPcommonly uses TCP

Application LayerApplication Layer

provide support for user applicationsprovide support for user applications need a separate module for each type of need a separate module for each type of

applicationapplication

Operation of TCP and IPOperation of TCP and IP

Addressing RequirementsAddressing Requirements

two levels of addressing requiredtwo levels of addressing required each host on a subnet needs a unique each host on a subnet needs a unique

global network addressglobal network address its IP addressits IP address

each application on a (multi-tasking) host each application on a (multi-tasking) host needs a unique address within the hostneeds a unique address within the host known as a portknown as a port

Operation of TCP/IPOperation of TCP/IP

Transmission Control Protocol Transmission Control Protocol ((TCP)TCP)

usual transport layer is (TCP)usual transport layer is (TCP) provides a reliable connection for transfer of provides a reliable connection for transfer of

data between applicationsdata between applications a TCP segment is the basic protocol unita TCP segment is the basic protocol unit TCP tracks segments between entities for TCP tracks segments between entities for

duration of each connectionduration of each connection

User Datagram ProtocolUser Datagram Protocol(UDP)(UDP)

an alternative to TCPan alternative to TCP no guaranteed deliveryno guaranteed delivery no preservation of sequenceno preservation of sequence no protection against duplicationno protection against duplication minimum overheadminimum overhead adds port addressing to IPadds port addressing to IP

TCP/IP ApplicationsTCP/IP Applications

have a number of standard TCP/IP have a number of standard TCP/IP applications such asapplications such as Simple Mail Transfer Protocol (SMTP)Simple Mail Transfer Protocol (SMTP) File Transfer Protocol (FTP)File Transfer Protocol (FTP) TelnetTelnet

OSIOSI

Open Systems InterconnectionOpen Systems Interconnection developed by the International developed by the International

Organization for Standardization (ISO)Organization for Standardization (ISO) has seven layershas seven layers is a theoretical system delivered too late!is a theoretical system delivered too late! TCP/IP is the de facto standardTCP/IP is the de facto standard

OSI LayersOSI Layers

OSI v TCP/IPOSI v TCP/IP

Standardized Protocol Standardized Protocol ArchitecturesArchitectures