DATA COMMUNICATION(ELA…)

PROTOCOLS AND ARCHITECTURE1

PROTOCOLS

Used for communications between entities in different systems

Must speak the same language

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KEY ELEMENTS OF A PROTOCOL Syntax

Data formatsSignal levels

SemanticsControl informationError handling

TimingSpeed matchingSequencing

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SERVER

RFLINK

PC

EXAMPLE: THREE-LAYER MODEL Communications can be said to involve

three agents:`

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EXAMPLE: THREE-LAYER MODEL Makes sense to organize the

communication task into three, relatively independent layers

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CommTask

EXAMPLE: THREE-LAYER MODEL Network Access Layer Functions

Exchange of data between the computer and the network

Sending computer provides address of destination to help in determining routing options

May invoke levels of service (i.e., priority) Software used in this layer depends on type of

network used

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EXAMPLE: THREE-LAYER MODEL Computer-Transport Layer Functions

Reliable data exchange Data arrive at destination application Same order in which they were sent

Independent of network being used Independent of application

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EXAMPLE: THREE-LAYER MODEL Application Layer Functions

Support for different user applications User applications refer to network applications Examples

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EXAMPLE: THREE-LAYER MODEL Addressing Requirements

Two levels of addressing required Each computer needs unique network address Each application on a multi-tasking computer needs a

unique address within the computerService Access Point (SAP)

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PROTOCOL ARCHITECTURES AND NETWORKS

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PROTOCOL DATA UNITS

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OSI – THE MODEL

Open Systems Interconnection (OSI) Developed by the International

Organization for Standardization (ISO) Seven layers A theoretical system delivered too late! TCP/IP is the de facto standard

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OSI – THE MODELLayering is the key! Each layer performs a subset of the

required communication functions Each layer relies on the next lower

layer to perform more primitive functions

Each layer provides services to the next higher layer

Changes in one layer should not require changes in other layers

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THE OSI ENVIRONMENT

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STANDARDIZATION WITHIN THE OSI FRAMEWORK

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ELEMENTS OF STANDARDIZATION

Protocol specificationOperates between the same layer on two

systemsMay involve different operating systemProtocol specification must be precise

Format of data units Semantics of all fields Allowable sequence of PDUs

Service definitionFunctional description of what is provided

AddressingReferenced by SAPs

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LAYER SPECIFIC STANDARDS

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ISO OSI REFERENCE MODEL

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Application Layer (7)

Presentation Layer (6)

Session Layer (5) Transport Layer (4)

Network Layer (3) Data Link Layer

(2) Physical Layer (1)

Application orientedNetwork oriented

NETWORK-DEPENDENT LAYERS

Physical LayerConcerned with the physical and electrical

interfaces b/w the user equipment and the network equipment

Responsible for the transmission of bitsAlways implemented using hardwarePhysical layer standards

RS-232-C RS-449 RS-422-A RS-423-A

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NETWORK-DEPENDENT LAYERS

Data Link LayerAssembles data bits into a block, or frameResponsible for ensuring error-free, reliable

transmission of dataRequests retransmission or correction if any

errors occurExample protocols

BSC SDLC HDLC PPP

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NETWORK-DEPENDENT LAYERS Network Layer

Responsible for appropriate routing of messages across a network

Only layer concerned with types of switching networks used to route data

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USE OF A RELAY

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APPLICATION-ORIENTED LAYERS Transport Layer

Responsible for: Monitoring the quality of the communications channel Selecting the most cost-efficient communication

service based on reliability required for a particular transmission

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APPLICATION-ORIENTED LAYERS

Session Layer Requests that a logical connection be established

based on the end user’s request Transfer a file

File location File destination

Controls any necessary log-ons and passwords Responsible for terminating connection

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APPLICATION-ORIENTED LAYERS

Presentation Layer Provides format and code conversion services

Printing operations Concerned with syntax and semantics of the

information transmitted File transfers b/w heterogeneous hosts

Data compression Data encryption

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APPLICATION-ORIENTED LAYERS Application layer

Provides access to the network for the end user Remote terminal access File transfer

Network management statistics and diagnostics can also be implemented in this layer

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TCP/IP PROTOCOL SUITE Dominant commercial protocol architecture Specified and extensively used before OSI Developed through the US Department of

Defense Used by the Internet

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TCP/IP LAYERS Physical Layer Network Access Layer Internet Layer Transport Layer (a.k.a., Host-to-host) Application Layer

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PHYSICAL LAYER Physical interface between data transmission

device (e.g. computer) and transmission medium or network Characteristics of transmission medium Signal levels Data rates

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NETWORK ACCESS LAYER Exchange of data between end system and

network Destination address provision Invoking services like priority Software depends on type of network

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INTERNET LAYER (IP) Systems may be attached to different

networks Routing functions across multiple networks Implemented in end systems and routers

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TRANSPORT LAYER Reliable delivery of data Ordering of delivery Uses Transmission Control Protocol (TCP)

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APPLICATION LAYER Support for user applications

HTTP Simple Mail Transfer Protocol (SMTP) Telnet FTP

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OPERATION OF TCP AND IP

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PDUS IN TCP/IP

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SOME PROTOCOLS IN TCP/IP SUITE

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OSI VS. TCP/IP

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STANDARDS

Required to allow for interoperability between equipment

AdvantagesEnsures a large market for equipment and

softwareAllows products from different vendors to

communicate Disadvantages

Freeze technologyMay be multiple standards for the same

thing e.g., military vs. commercial

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STANDARDS ORGANIZATIONS

Internet Society ISO International Telecommunications Union –

Telecommunications Sector (ITU-T) ATM forum

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