1 Lecture #2: Components of Network. Communication Subnetwork C o n t e n t s l Network Architecture: –Terminal Network –Computer Network l Data Transmission Modes –Circuit Switching –Message switching –Packet Switching virtual channelsvirtual channels datagram switchingdatagram switching l Communication Subnetwork l Network Components

2 Network Architecture: Terminal Network l From Terminal Complex to Terminal Network l Terminal Network Structure: –host, –communication processor, –concentrator, –terminal processor

3 Network Architecture: Computer Network l From Terminal Network to Computer Network: –distributed control –distributed resources –remote access l Network Range: –LAN (local area) –MAN (metropolitan area) –WAN (wide area) –Global Network l Network Topology: star, ring, tree, complete, irregular.

4 Data Transmission Modes - Circuit Switching l Messages: information transmitted between source and receiver l Circuit switching: set of connected channels for monopoly use during whole transmission (e.g. phone lines) l Message switching: dynamical routing of the messages; intermediate buffering (drawback: long buffers) l Packet switching: messages divided in fixed size short packets (e.g 1Kb -10 Kb)

5 Packet Switching - Transmission Modes l Transmission Modes l Virtual Channel: sequenced packets’ order provided by the communication subnetwork l 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.

6 Communication Subnetwork l 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 l Network Components: hosts, routers, hubs, terminals, concentrators, terminal processors, synchronous and asynchronous adapters, modems, interfaces, synchronous and asynchronous multiplexor, intersystem adapter (host-host).

7 Communication Subnetwork l 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)

8 DTE/DCE Interfaces l Interface - hardware or software components for interconnection between different type devices l Serial Interfaces: bit slice transmission l Parallel Interfaces: byte slice transmission

9 Serial Interfaces l Main Serial Interfaces l 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 bussesInformation 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”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)Timing busses: TC_1(15), TC_2(24), RC(17) Ground linesGround lines ReservedReserved

10 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 ) marks the start and the end of the information block. “Zero bit insertion” procedure for differing the info data from the TAG.