OSI MODEL

Sunawar Khan MS(CS)

IIUI

SK Ahsan

PROTOCOL STACK•Protocol Stack is a combination of different protocol.

•All these protocols works together to perform specific task.

•Every Layer Hs different protocol.

•We discuss aboouut layer

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LAYERED TASK•We use the concept of layers in our daily life.

•As an example would two friends who communicate through postal email.

•The process of sending a letter to a friend would be complex if there are no service available from the post office

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LAYERED TASKSender Receiver

The letter is written put in an envelope, and

dropped in a mailbox

The letter is delivered to carrier by the post office

The letter is carried from the mailbox to a post

office

The letter is picked up, removed from the envelop, and read

The letter is delivered to carrier by the post office

The letter is carried from the mailbox to a post

officeMiddle Layer

Lower Layer

Higher Layer

Parcel is Carried from the source to the destination

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THE OSI MODEL• ISO is an organization which is established in 1947.

•AN ISO standard that covers all aspects of network communication.

•Network communication model is defined in OSI.

• It was first introduced in the late 1970s, 1983

ISO is the organization.OSI is the model.

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WHY OSI MODEL•OSI model decide how different equipment from different vendors can communicate with one another• Communication process is divided into different subtasks.•Using OSI model NETWORK HARDWARE and SOFTWARE can easily communicate with one another. • If any kind of change is required then it occurs only in required layer.

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7 LAYERS OF OSI MODELApplication

Network process to ApplicationPresentation

Data Representation and Encryption

SessionInterhost Communication

TransportEnd to End Connection and

ReliabilityNetwork

Path Determination and IP(Logical) Add.

DataLinkMAC and LLC(Physical Addr)

PhysicalMedia, Signal and Binary

Transmission Send Packet in the form of BITS

Error Checking and Physical Connection

Sequencing and Address Information

Errors Control

Traffic Flow Information

Formatting and Encryption of Packets data

Accept request to CommunicateDATA

DATA

DATA

Segment

Packets

Frames

Bits

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MNEMONICS•The following mnemonics may help you remember the layers sequence and names. •All People Seems To Need Data Processing.•Please Do Not Take Sales People’s Advice.•People Design Networks To Send packets Accurately•Always Put Some Thoughts Into Designing Programs.

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LAYERING AND INTERNETWORKING

•Communication environments separate the networking functions and application processing are called LAYERING.• OSI divides the big task of host-to-host networking called INTERNETWORKING in to a vertical stack.• This OSI stack contains the seven numbered layers ,these indicate distinct functions.

CLIENT AND SERVER

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Application

Presentation

Session

Transport

Network

Datalink

Physical

Client Server

Application

Presentation

Session

Transport

Network

Datalink

PhysicalPhysical Link

Logical Link

SK Ahsan Figure:The interaction between layers in the OSI model

OSI Layers Interaction

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Transmission Medium

Figure: An exchange using the OSI model

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ARCHITECTURE DESCRIPTION

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PHYSICAL LAYER

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PHYSICAL LAYER• It transmits data over physical medium or on network like hardware like cables, cards, electrical, optical, mechanical and functional interface to the medium.• It handles the transmission of raw bits over a communication link.• It is responsible for transmitting bit(ZERO and ONE) by providing signaling of the message and the interface between the sender or receiver and the medium.

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PHYSICAL LAYER• Physical Layer must decide the following• Characteristics of Media• Representation of Bits•Data Rate• Synchronization• Line Configuration• Transmission Mode

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

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DATALINK LAYER

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DATA LINK LAYER• Frames not raw bits are actually delivered to the host.• The data link layer is responsible for moving frames from one hop (node) to the next.•Manage physical layer communication between connecting systems.• It is responsible for providing node to node communication on a single, local network.

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HOP TO HOP DELIVERY

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FUNCTIONS OF DATA LINK LAYER• It must provide an address mechanism that enable messages to be

delivered to the correct nodes. • Data units at the Data Link layer are most commonly called

frames, although the term packets is used with some protocols.• The single layer actually incorporates two sub-layers as IEEE

Logical Link Control Model.• The Lower of the two sub-layers is called the MAC and the upper

sub-layer is the LLC.• The MAC layer provides local addressing. Error correction and in

some cases includes a field to distinguish the frame type from the other types.

• Example of Data Link Standards include frame relay, ETHERNET, Token Ring and FDDI.

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DATA LINK LAYER

•Datalink layer must decide the following•Framing •Flow control•Error Control•Access Control

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

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NETWORK LAYER

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SOURCE TO DESTINATION DELIVERY

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NETWORK LAYER• The network layer handles routing among nodes within a packet switched network.• The network layer operates independently of the physical medium, which is a concern of the physical layers.• Routers are network layer devices, they can be used to forward packets between physically different networks. • It adds a header to the message that includes the source and destination network address.• This combination of data plus the network layer is called a PACKETS

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NETWORK LAYER• It translates logical addresses and names into physical

addresses for Packets Delivery.• The addressing which makes this delivery can be thought of

as a universal address as compared to the local addressing of the MAC.• It determines routes for sending, managing network traffic

problems, packet switching, routing, data congestion and reassembling data. • It control end-to-end flow of segmentation and reassembly

functions of large packets of data which exceed the Maximum Transmission Units.• The Internet Protocol(IP) is the most common example.

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NETWORK LAYER

•Some responsibilities of the network layer are as follows•Logical Addressing

•Routing

The network layer is responsible for the delivery of individual packets from

the source host to the destination host.

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TRANSPORT LAYER

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RELIABILITY

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TRANSPORT LAYER

• It translates system names into addresses.• The unit of data exchange is commonly called MESSAGE rather

than a packet or frame. • It divides messages into fragments that fit within the size

limitation established by the network.• It allows users to segments/reassemble several upper layer

application on to the same transport data stream. • It ensure host to host session connection. • This layer is responsible for addressing, determining network

traffic problems, packet switching, routing, congestion and reassembling data at receiving end to recover the original message.

TRANSPORT LAYER

• It ensures that the segments delivered will be acknowledge back too the sender. • It provides retransmission of segments those are not acknowledged.• Puts segments back into their correct sequence at the destination. • To enable packets reassemble in their original order, this layer include a MESSAGE SEQUENCE NUMBER in its header.• Sometimes it provides a multiplexing between the same two end-points.• Delivery may be GUARANTEED or CONNECTION-ORIENTED streams like TCP or UDP SK Ahsan

TRANSPORT LAYER

• It is also responsible for delivering message from a specific process on one computer to the corresponding process on the destination computer. •Transport layer assigns a service access point to each packet. In TCP/IP terms that is called PORT.•One more responsibility of the transport layer is DETECTING ERRORS In transmitting data.

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TRANSPORT LAYER•Some responsibilities of the transport layer are as follows•Service Point Addressing•Segmentation and Re-assembly•Connection Control•Flow Control•Error Control

The transport layer is responsible for the delivery

of a message from one process to another.

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SESSION LAYER

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SESSION LAYER

• It establishes, manages and terminates session between application.• It provides mechanism for managing end-user, host, process

operations termination and restart procedures.• It is responsible for dialog control between nodes. Dialog is a formal

conversation in which two nodes agree to exchange data.• The communication across a network can take place and controlled

in one of three dialog modes are simplex, Half Duplex and Full Duplex.• Testing for out-of-sequence packet is handles also.• Session enables communication in organized manner in three

phases as Connection Establishment, Data Transfer and Connection Release.

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PRESENTATION LAYER

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PRESENTATION LAYER• This layer provides data communication and code formatting.• It provides a way for a remote host to inform the local client

how to present the data to the application or client.• It ensures that the data that arrives from the network can be

used by the application, and information send by the application can be transmitted on the network.• It directly translates data from one format to another. • It provides data encryptioiin, decryption, compression and

decompression. • It delivers and format information for application layer

processing.

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PRESENTATION LAYER•Presentation Layer perform the following•Data Reformatting•Encryption

The presentation layer is responsible for translation,

compression, and encryption.

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APPLICATION LAYER

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APPLICATION LAYER• The application layer provides different services to user application. • It interfaces directly to these services and provide conversion between associated application process.• It contains a variety of protocols that are commonly needed.• Another application layer function is file transfer. • Different file system have different file naming conventions. • Transferring a file between two different system requires handling all incompatibilities.

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APPLICATION LAYER•Application Layer provide different information services as•File Transfer•Mail Services•Directory Services

The application layer is responsible for

providing services to the user.

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SUMMARY

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REFERENCES• Behroz A Frozen, Textbook Chapter 2, Topic 2.1, 2.2• Larry and Peterson, Textbook Chapter 1

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ABOUT• Sunawar Khan Ahsan

• Sk_ahsan38@yahoo.com• +923334892200

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