OSI Model

OSI MODEL:

The open systems interconnection (OSI) model was developed by the International Organization for Standardization (ISO) as a model for a computer communications architecture and as a framework for developing protocol standards. It consists of seven layers:

•  Application
•  Presentation
•  Session
•  Transport
•  Network
•  Data Link
•  Physical

  

Function of OSI Layers

• Layer # 1 (Physical Layer)

• Physical characteristics of interfaces and media.
• Representation of bits (types of encoding)
• Date rate (transmission rate (duration of bits))
• Synchronization of bits
• Line configuration (point-to-point configuration, multipoint configuration)
• Physical topology (mesh, ring, bus topology etc)
• Transmission mode (simplex, half/full duplex)

• Layer # 2 (Data Link Layer)

• Frames
• Framing
• Physical addressing (source/destination address)
• Flow control (prevent overwhelming)
• Error control
• Access control

• Layer # 3 (Network Layer)

• Packets
• Source to destination delivery of packets
• Logical addressing
• Routing

• Layer # 4 (Transport Layer)

• Segment
• Source to destination (end-to-end) delivery of entire message
• Service point addressing
• Segmentation and reassembly
• Connection control (connection oriented / connection less)
• Flow control (perform end to end)
• Error control (perform end to end)

• Layer # 5 (Session Layer)

• Establish, maintain, synchronize and terminates session between two
• communication systems
• Dialog control
• Synchronization

• Layer # 6 (Presentation Layer)

• Translation
• Encryption / decryption
• Compression

• Layer # 7 (Application Layer)

• Network virtual terminal
• File transfer, access and management (FTAM)
• Mail services
• Directory services