Network Applications and Layered Architectures Protocols OSI Reference

Network Applications and Layered Architectures Protocols OSI Reference Model

What is Computer Networks? l A collection of autonomous computers interconnected by a single technology l Interconnected via: Copper wire l Fiber optics l Microwaves l Infrared l Communication satellites, etc. l

Open Systems Interconnection l l Network architecture: l Definition of all the layers l Design of protocols for every layer By the 1970 s every computer vendor had developed its own proprietary layered network architecture Problem: computers from different vendors could not be networked together Open Systems Interconnection (OSI) was an international effort by the International Organization for Standardization (ISO) to enable multivendor computer interconnection

7 -Layer OSI Reference Model Application End-to-End Protocols Application Layer Presentation Layer Session Layer Transport Layer Network Layer Data Link Layer Physical Layer Communicating End Systems One or More Network Nodes

Headers & Trailers l l Each protocol uses a header that carries addresses, sequence numbers, flag bits, length indicators, etc… CRC check bits may be appended for error detection Application APP DATA Application Layer AH APP DATA Application Layer TH AH APP DATA Transport Layer NH TH AH APP DATA Network Layer Transport Layer Network Layer Data Link Layer Physical Layer DH NH TH AH APP DATA CRC bits Data Link Layer Physical Layer

Classification of interconnected processors by scale.