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Lecture #2: Components of Lecture #2: Components of Network. Communication Network. Communication

SubnetworkSubnetworkC o n t e n t s C o n t e n t s Network Architecture:Network Architecture:

– Terminal NetworkTerminal Network– Computer NetworkComputer Network

Data Transmission Modes Data Transmission Modes – Circuit SwitchingCircuit Switching– Message switchingMessage switching– Packet SwitchingPacket Switching

• virtual channelsvirtual channels• datagram switchingdatagram switching

Communication SubnetworkCommunication Subnetwork Network ComponentsNetwork Components

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Network Architecture: Network Architecture: Terminal Network Terminal Network

From Terminal Complex to From Terminal Complex to Terminal NetworkTerminal Network

Terminal Network Structure: Terminal Network Structure: – host, host, – communication processor, communication processor, – concentrator, concentrator, – terminal processor terminal processor

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Network Architecture: Network Architecture: Computer NetworkComputer Network

From Terminal Network to Computer From Terminal Network to Computer Network:Network:– distributed controldistributed control– distributed resourcesdistributed resources– remote accessremote access

Network Range:Network Range:– LAN (local area)LAN (local area)– MAN (metropolitan area)MAN (metropolitan area)– WAN (wide area)WAN (wide area)– Global NetworkGlobal Network

Network Topology: star, ring, tree, Network Topology: star, ring, tree, complete, irregular.complete, irregular.

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Data Transmission Data Transmission Modes - Circuit Modes - Circuit

SwitchingSwitching Messages: information transmitted Messages: information transmitted between source and receiverbetween source and receiver

Circuit switching: set of connected Circuit switching: set of connected channels for monopoly use during channels for monopoly use during whole transmission (e.g. phone lines)whole transmission (e.g. phone lines)

Message switching: dynamical Message switching: dynamical routing of the messages; routing of the messages; intermediate buffering (drawback: intermediate buffering (drawback: long buffers)long buffers)

Packet switching: messages divided Packet switching: messages divided in fixed size short packets (e.g 1Kb -in fixed size short packets (e.g 1Kb -10 Kb) 10 Kb)

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Packet Switching - Packet Switching - Transmission ModesTransmission Modes

Transmission ModesTransmission Modes Virtual Channel: sequenced packets’ order Virtual Channel: sequenced packets’ order

provided by the communication subnetworkprovided by the communication subnetwork Datagram Switching: packets (called Datagram Switching: packets (called

datagrams) are provided with destination datagrams) are provided with destination address and ordering number fields. Routing address and ordering number fields. Routing is random for any datagram. The message is is random for any datagram. The message is completed only in the end station. completed only in the end station. Advantages: speed and traffic balancing; Advantages: speed and traffic balancing; Drawbacks: communication overload.Drawbacks: communication overload.

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Communication SubnetworkCommunication Subnetwork Specialized equipment for data tranmission-Specialized equipment for data tranmission-

– separates data processing and communication separates data processing and communication

tasks: hosts perform user data processingtasks: hosts perform user data processing

– communication devoted resources:transmission communication devoted resources:transmission

channels; buffers; error control processing; fault channels; buffers; error control processing; fault

tolerant algorithms tolerant algorithms

Network Components: Network Components: hosts, routers, hubs, hosts, routers, hubs,

terminals, concentrators, terminal processors, terminals, concentrators, terminal processors,

synchronous and asynchronous adapters, modems, synchronous and asynchronous adapters, modems,

interfaces, synchronous and asynchronous multiplexor, interfaces, synchronous and asynchronous multiplexor,

intersystem adapter (host-host).intersystem adapter (host-host).

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Communication Communication SubnetworkSubnetwork

Interface standards:Interface standards:

– DTEDTE (Data Terminal Equipment): (Data Terminal Equipment): host, terminal or any end processing host, terminal or any end processing devicedevice

– DCEDCE (Data Circuit-Termination (Data Circuit-Termination Equipment): modem i.e. data Equipment): modem i.e. data transmission unittransmission unit

– Standard Interface Standard Interface RS 232RS 232 (evolved in RS 422 / EIA-422)(evolved in RS 422 / EIA-422)

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DTE/DCE InterfacesDTE/DCE Interfaces

Interface - hardware or Interface - hardware or software components for software components for interconnection between interconnection between different type devicesdifferent type devices

Serial Interfaces: bit slice Serial Interfaces: bit slice transmissiontransmission

Parallel Interfaces: byte slice Parallel Interfaces: byte slice transmission transmission

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Serial InterfacesSerial Interfaces Main Serial InterfacesMain Serial Interfaces RS 232RS 232::

– voltage levels: voltage levels: [-15,-3] [+3,+15][-15,-3] [+3,+15]– bussesbusses

• Information busses- Information busses- TxDTxD(2) , (2) , RxDRxD (3): bit-slice (3): bit-slice (serial) data transmit from-DTE-to-DCE/receive (serial) data transmit from-DTE-to-DCE/receive from-DCE-to-DTE depending on control bussesfrom-DCE-to-DTE depending on control busses

• Control busses: Control busses: RTSRTS(4), (4), DTRDTR(20), (20), CTSCTS (5), (5), DSRDSR (6): “1” allow transmit/receive or denote “ready” (6): “1” allow transmit/receive or denote “ready” device; “0” forbid transmit/recive, or device “not device; “0” forbid transmit/recive, or device “not ready”ready”

• Timing busses: Timing busses: TC_1TC_1(15), (15), TC_2TC_2(24), (24), RCRC(17)(17)• Ground linesGround lines• ReservedReserved

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Information Information Transmission Protocols Transmission Protocols

– Byte Oriented ProtocolsByte Oriented Protocols - for symbol - for symbol transmission (e.g. using ASCII) transmission (e.g. using ASCII) synchronization symbols (bytes) in the synchronization symbols (bytes) in the beginning and the end of each block beginning and the end of each block

– Bit Oriented ProtocolsBit Oriented Protocols - for symbol and - for symbol and data transmission - binary coding of text and data transmission - binary coding of text and data (universal use). Special sequence data (universal use). Special sequence called TAG (usually called TAG (usually 0111111001111110) marks the ) marks the start and the end of the information block. start and the end of the information block. “Zero bit insertion” procedure for differing “Zero bit insertion” procedure for differing the info data from the TAG.the info data from the TAG.