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University of Education 2

LectureRoadmap

Need of a Layered Architecture OSI Model

7 Layers of OSI Model Functional Details of OSI Layers

Physical Layer Data Link Layer Network Layer Transport Layer Session Layer

Presentation Layer Application Layer


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Layered Architecture

Design Philosophy of Layered Architecture The complex task of communication is broken into

simpler sub-tasks or modules 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 Helps in troubleshooting and identifying the problem


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An example Sending a letter


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OSI Model

To standardize the design of communicationsystem, the ISO created the OSI model.

Open Systems Interconnection Developed by the International Organization

for Standardization (ISO) Contains Seven layers It describes the functions to be performed at

each layer


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OSI Model

ISO Established in 1947ISO Established in 1947 ISO standard that covers all aspects of networkISO standard that covers all aspects of network

communications is the Open Systems Interconnectioncommunications is the Open Systems Interconnection((OSIOSI ) model.) model.

First introduced in the late 1970s.First introduced in the late 1970s. A layer model 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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ISO is the organization.OSI is the model.

Note


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OSI Model

ApplicationPresentation

Session Transport

NetworkData Link

Physical


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Peer-to-Peer Process


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An exchange using the OSI model


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OSI Model Physical Layer

Physical Physical interface between devices handles the transmission of bits over a

communications channel Choice of Wired / wireless medium Data is converted into signals Includes voltage levels, connectors, media

choice modulation techniques EIA/TIA-232, RJ45, NRZ.


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The physical layer is responsible for movements of individual bits from one hop (node) to the next.

Note


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OSI Model Data Link Layer

Data Link Transforms data into a frame Means of activating, maintaining and

deactivating a reliable link Error detection and control Flow Control Higher layers may assume error free

transmission Examples :- Ethernet, Frame Relay, FDDI.


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Data Link Layer


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The data link layer is responsible for movingframes from one hop (node) to the next.

Note


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OSI Model Network Layer

Network Transport of information Higher layers do not need to knowabout underlying technology

Responsible for creating, maintainingand ending network connections

Transfers a data packet from node tonode within the network .

Routing Not needed on direct links Examples :- IP, IPX, AppleTalk.


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Network Layer


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The network layer is responsible for the delivery of individual packets from the source host to thedestination host.

Note


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Transport Layer

Transport Exchange of data between end

systems (end to end flow control)

Error free In sequence

Quality of service Layer 4 protocols include TCP (Transmission

Control Protocol) and UDP (User DatagramProtocol).


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Transport Layer


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The transport layer is responsible for the deliveryof a message from one process to another.

Note


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OSI Model Session Layer

Session Control of dialogues between

applications Half Duplex Full Duplex

Synchronization Points (backup points)

Examples :- SQL, ASP(AppleTalk SessionProtocol), NETBIOS, RPC, PAP.


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The session layer is responsible for dialog control andsynchronization.

Note


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OSI Model PresentationLayer

Presentation Data formats and coding

Data compression Encryption Examples :- JPEG, MPEG, ASCII,

EBCDIC, HTML.


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The presentation layer is responsible for translation,compression, and encryption.

Note


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OSI Model ApplicationLayer

Application Layer where the application using thenetwork resides.

Common network applications include remote login file transfer e-mail

web page browsing etc. Means for applications to access OSIenvironment


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The application layer is responsible for providingservices to the user.

Note


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Summary of layers


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OSI Layers


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The OSI Environment


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The OSI Environment


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TCP/IP Protocol Suit

TCP/IP suite is the set of protocols thatimplement the protocol stack on whichthe Internet runs. It is sometimes calledthe Internet Model.

This model consists of five orderedlayers

In a protocol stack, each layer solves aset of problems involving thetransmission of data, and provides awell-defined service to the higher layers

Developed by research foundation byUS department of defense


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Internet layers


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TCP/IP Protocol ArchitectureModel


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Some Protocols in TCP/IP Suite

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