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
