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The Open Systems Interconnection (OSI) model (ISO/IEC 7498-1) is a conceptual model that characterizes and standardizes the internal functions of a communication system by partitioning it into abstraction layers. The model is a product of the Open Systems Interconnection project at the International Organization for Standardization (ISO).
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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.