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Lecture #2: Components of Network. Communication Subnetwork C o n t e n t s • Network Architecture: • Terminal Network • Computer Network • Data Transmission Modes • Circuit Switching • Message switching • Packet Switching • virtual channels • datagram switching • Communication Subnetwork • Network Components 2 4 5 6 9
Network Architecture: Terminal Network • From Terminal Complex to Terminal Network • Terminal Network Structure: • host, • communication processor, • concentrator, • terminal processor
Network Architecture: Computer Network • From Terminal Network to Computer Network: • distributed control • distributed resources • remote access • Network Range: • LAN (local area) • MAN (metropolitan area) • WAN (wide area) • Global Network • Network Topology: star, ring, tree, complete, irregular.
Data Transmission Modes - Circuit Switching • Messages: information transmitted between source and receiver • Circuit switching: set of connected channels for monopoly use during whole transmission (e.g. phone lines) • Message switching: dynamical routing of the messages; intermediate buffering (drawback: long buffers) • Packet switching: messages divided in fixed size short packets (e.g 1Kb -10 Kb)
Packet Switching - Transmission Modes • Transmission Modes • Virtual Channel: sequenced packets’ order provided by the communication subnetwork • Datagram Switching: packets (called datagrams) are provided with destination address and ordering number fields. Routing is random for any datagram. The message is completed only in the end station. Advantages: speed and traffic balancing; Drawbacks: communication overload.
Communication Subnetwork • Specialized equipment for data tranmission- • separates data processing and communication tasks: hosts perform user data processing • communication devoted resources:transmission channels; buffers; error control processing; fault tolerant algorithms • Network Components: hosts, routers, hubs, terminals, concentrators, terminal processors, synchronous and asynchronous adapters, modems, interfaces, synchronous and asynchronous multiplexor, intersystem adapter (host-host).
Communication Subnetwork • Interface standards: • DTE (Data Terminal Equipment): host, terminal or any end processing device • DCE (Data Circuit-Termination Equipment): modem i.e. data transmission unit • Standard Interface RS 232(evolved in RS 422 / EIA-422)
DTE/DCE Interfaces • Interface - hardware or software components for interconnection between different type devices • Serial Interfaces: bit slice transmission • Parallel Interfaces: byte slice transmission
Serial Interfaces • Main Serial Interfaces • RS 232: • voltage levels: [-15,-3] [+3,+15] • busses • Information busses- TxD(2) , RxD (3): bit-slice (serial) data transmit from-DTE-to-DCE/receive from-DCE-to-DTE depending on control busses • Control busses: RTS(4), DTR(20), CTS (5), DSR (6): “1” allow transmit/receive or denote “ready” device; “0” forbid transmit/recive, or device “not ready” • Timing busses: TC_1(15), TC_2(24), RC(17) • Ground lines • Reserved
Information Transmission Protocols • Byte Oriented Protocols - for symbol transmission (e.g. using ASCII) synchronization symbols (bytes) in the beginning and the end of each block • Bit Oriented Protocols - for symbol and data transmission - binary coding of text and data (universal use). Special sequence called TAG (usually 01111110) marks the start and the end of the information block. “Zero bit insertion” procedure for differing the info data from the TAG.