A TECHNICAL SEMINAR

ON OSI MODEL

OSI modelOSI model OSI LayersOSI Layers InteractionInteraction between layers in the OSI modelbetween layers in the OSI model Data Exchange Using OSI ModelData Exchange Using OSI Model Headers and TrailersHeaders and Trailers Physical LayerPhysical Layer Data Link LayerData Link Layer Network Layer Network Layer Transport LayerTransport Layer Session LayerSession Layer Presentation LayerPresentation Layer Application LayerApplication Layer Summary of LayersSummary of Layers ConclusionConclusion

CONTENTSCONTENTS

OSI Model

• OSI or Open Systems Interconnection model is an ISO standard that covers all aspects of network communications.

• Open system: allows different systems to communicate regardless of their underlying architecture or supplier

• OSI model allows complete transparency between otherwise incompatible systems.

OSI Model • OSI model consists of seven separate

layers, each defines a segment of the process of moving information across a network

– physical (layer 1)

– data link (layer 2)

– network (layer 3)

– transport (layer 4)

– session (layer 5)

– presentation (layer 6)

– application (layer 7)

SEVEN LAYERS OF THE OSI MODEL

Interaction between layers in the OSI model

Data Exchange Using OSI Model

Headers and Trailers I

• Each layer adds own information to the message it receives from the layer just above it

• On the receive side, layers strip information added on peer layer of transmit side before passing the message to next higher layer

• Added “control data” is placed to the beginning (header) or/and end of a data packet (trailer)

Headers and Trailers II

• The whole package (packet or frame) is passed to the layer just below it.

• Headers are added to the message at layers 6, 5, 4, 3, and 2. A trailer is added only at layer 2.

• Examples of header info: checksum, sender/receiver address, service type

Physical Layer

Physical Layer• Purpose: Coordinates the functions

required to transmit and receive streams of bits, over physical communication medium

• Major issues: ·  what type of signals?

·  how are bits represented by signals?

·  what physical medium to use?

·  interface: electrical and mechanical

·  How bits are synchronized in Tx and Rx?

Data Link Layer

Node-to-node delivery

Data Link layer (1)

• Purpose: error-free delivery of frames between two systems on the same network (Node-to-Node)

Major issues: 

• what information goes into header/trailer?

• how are stations addressed? Physical Address

• how are transmission errors detected and corrected (Error Control)

Data Link layer (2)

• how is transmission flow between stations regulated? Flow Control

 • how is access to “shared transmission

channel” regulated? Access Control • For LANs, this layer has been

subdivided into two sub-layers: “logical link control” (LLC) and “media access control” (MAC) sub-layers

Data Link Layer Example

Network Layer

Source-to-destination delivery

Network Layer• Purpose: source to destination delivery

of packet , possibly across multiple networks 

Major Issues: • what info goes into header? (e.g. end-to-

end (logical) addresses: source and destination)  

• how is packet routed from source to destination? 

• regulation transmission flow between network nodes

Network Layer Example

Network Layer Example

Transport layer• Purpose: error free source to destination

delivery of (entire) messages

• how is message segmented into packets?

• how are packets reassembled into messages?

• how are packets delivered to correct application (port address)?

• how is the connection between source and

destination? connectionless or connection oriented

Transport Layer

Reliable process-to-process delivery of a message

Session Layer

Presentation Layer

Application Layer

FTP FTPSMTP TelnetSMTPTelnet

Summary of Layer Functions

Conclusion

The International Standard Organization created a model called the open system interconnection, which allows diverse system to communicate. The seven layer OSI model provides guidelines for the developments universally compatible networking protocol.