Computer and Data Communications Read Chapters 1 & 2

A Communications Model output information Input device Input device Transmiter Transmission medium Transmission medium Receiver Output Devices Output Devices input information input data transmitted signal received signal output data data : A representation of facts, concepts in a formalized manner suitable for communication information : The meaning that is currently assigned to data by means of the conventions applied to those data

Communication Tasks Transmission system utilization Interfacing Signal generation Exchange management Error detection and correction System management Flow control Addressing Routing Recovery Message formatting Protection

Data Communication Network Communication Network Communication Network Node Network Station

Data communication networks Public Switched Telephone Network (PSTN) Local Area Network (LAN) Leased lines Public switched data network (PSDN) Integrated services digital network (ISDN)

PSTN modem modem link via PSTN PSTN

LANhub hub hub hub 1st floor 2nd floor 3rd floor 4th floor router confined geographical area confined geographical area under single management under single management high data rate high data rate server station station station

Leased lines Lease pubic circuits to connect different sites Communication channel is privated LAN Voice LAN Voice LAN Voice leased circuit

PSDN PSDN= Public Switched Data Network = LAN PSDN PSDN is designed specifically for the transmission of data rather than voice Communication is shared

ISDN ISDN NTE NTE = Network termination equipment ISDN = Integrated services digital network Using ISDN to carry both voice and data

Computer Communication Architecture Communication-related messages Network interface File and file transfer command Communication network File transfer application Communications service module Network access module Computer A File transfer application Communications service module Network access module Computer B

Three-layer's model Applications Transport Network access

Communication architectures and networks Applications Transport Network access Applications Transport Network access Applications Transport Network access Communication network Service Access Point Network Address

Protocol layers Transport protocol Network Access Protocol Application protocol Application Transport Network access Computer A Application Transport Network access Computer B

Protocol data unit Application data Application data Transport header Transport header Transport header Transport header Network header Network header Transport protocol data unit (TPDU) Network protocol data unit (NPDU) Application data Application data Application data control info + data in each layer = protocol data unit (PDU)

OSI reference Model Layer 1 Physical link Layer 2 Data link layer Layer 3 Network layer Layer 4 Transport layer Layer 5 Session layer Layer 6 Presentation layer Layer 7 Application layer developed by ISO (International Standards Organization)

Standards Integrated computer and telecommunications industry Integrated computer and telecommunications industry ISO ITU-T International Standards (Open Systems Interconection) Telecommunications Industry Telecommunications Industry ITU-T CEPT ANSI Interface standards (multi-vendor systems) Computer Industry Computer Industry Proprietary standards (closed systems) ECMA EIA IEEE