Source generates data to be transmitted Transmitter Converts data into transmittable signals Transmission System Carries data Receiver Converts received signal into data Destination Takes incoming data | William Stallings Data and Computer Communications Chapter 1 Introduction A Communications Model Source generates data to be transmitted Transmitter Converts data into transmittable signals Transmission System Carries data Receiver Converts received signal into data Destination Takes incoming data * Simplified Communications Model - Diagram * Key Communications Tasks Transmission System Utilization Interfacing Signal Generation Synchronization Exchange Management Error detection and correction Addressing and routing Recovery Message formatting Security Network Management * Simplified Data Communications Model * Networking Point to point communication not usually practical Devices are too far apart Large set of devices would need impractical number of connections Solution is a communications network * Simplified Network Model * Wide Area Networks Large geographical area Crossing public rights of way Rely in part on common carrier circuits Alternative technologies Circuit switching Packet switching Frame relay Asynchronous Transfer Mode (ATM) * Circuit Switching Dedicated communications path established for the duration of the conversation . telephone network * Packet Switching Data sent out of sequence Small chunks (packets) of data at a time Packets passed from node to node between source and destination Used for terminal to computer and computer to computer communications * Frame Relay Packet switching systems have large overheads to compensate for errors Modern systems are more reliable Errors can be caught in end system Most overhead for error control is stripped out * Asynchronous Transfer Mode ATM Evolution of frame relay Little overhead for error control Fixed packet (called cell) length Anything from 10Mbps to Gbps Constant data rate using packet switching technique * Integrated Services Digital Network ISDN Designed to replace public telecom system Wide variety of services Entirely digital domain * Local Area Networks Smaller scope Building or small . | William Stallings Data and Computer Communications Chapter 1 Introduction A Communications Model Source generates data to be transmitted Transmitter Converts data into transmittable signals Transmission System Carries data Receiver Converts received signal into data Destination Takes incoming data * Simplified Communications Model - Diagram * Key Communications Tasks Transmission System Utilization Interfacing Signal Generation Synchronization Exchange Management Error detection and correction Addressing and routing Recovery Message formatting Security Network Management * Simplified Data Communications Model * Networking Point to point communication not usually practical Devices are too far apart Large set of devices would need impractical number of connections Solution is a communications network * Simplified Network Model * Wide Area Networks Large geographical area Crossing public rights of way Rely in part on common carrier circuits Alternative technologies Circuit switching .
