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14 장 SWITCHING :A NETWORK LAYER FUNCTION

14.1 회선교환 (Circuit Switching)

14.2 패킷 교환 (Packet Switching)

14.3 메시지 교환 (Message Switching)

14.4 네트워크층14.5 요약

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Switching(cont’d)Switching

~ whenever we have multiple devices, we have the problem the problem of how to connect them to make one-one-one communication possible.

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Switching(cont’d)

Switching method

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14.1 Circuit Switching~ create a direct physical connection between

two devices such as phones or computer.Circuit-switched network

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Circuit Switching(cont’d)Circuit Switching

~ is a device with n inputs and m outputs that creates a temporary connection between an input link and output link.

A circuit switch

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Circuit Switching(cont’d)n-by-n folded switch can connect n lines in

full-duplex mode

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Circuit Switching(cont’d)Circuit Switching

~ can use either two technologies.

Switching

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Circuit Switching(cont’d)

Space-Division Switches the paths in the circuit are separated from each

other spatially(crossbar switch)

Crossbar switch~ connect n input to m output in a grid, using

electronic microswitch(transistor) at each crosspoint.

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Circuit Switching(cont’d)

Crossbar switch

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Circuit Switching(cont’d)Limitation of crossbar switch

The number of switch(huge size): connect n inputs by m output -- require n * m crosspoint.(ex : 1000 input, 1000 output → 1,000,000 crosspoint)

inefficient~ fewer than 25% of the crosspoint are in use at a given time.

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Circuit Switching(cont’d)Multistage Switches

~ devices are linked to switches that, in turn are linked to a hierarchy of other switches

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Circuit Switching(cont’d)

Multiple paths

a. b.

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Circuit Switching(cont’d)Block

~ compare the number of crosspoints in a 15-by-15 single-stage crossbar switch with the 15-by-15 multistage switch.

single-stage switch~ need 225 crosspoint(15 * 15)

multistage switch~ first-stage : 10 crosspoint(5 * 2) *3 = 30 crosspoint~ second-stage : 9 crosspoint(3 *3) * 2 = 18 crosspoint ~ third-stage : 10 crosspoint(5 * 2) *3 = 30 crosspoint

total number of crosspoint : 78

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Circuit Switching(cont’d)

Time-Division Switch~ is accomplished using TDM(Time-division

multiplexing) and TSI(Time-Slot Interchange)

TSI - change the ordering of the slots based on the desired connections.

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Circuit Switching(cont’d)

Time-division multiplexing, without and with a time-slot interchange(TSI) - No switching

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Circuit Switching(cont’d)

Time-division multiplexing, without and with a time-slot interchange(TSI) - Switching

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Circuit Switching(cont’d)TSI 동작과정

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Circuit Switching(cont’d)

Space-and Time-Division Switching Combinations~ combine space-division and time-division

technology to take advantage of the best of both

TST(time-space-time) TSST(time-space-space-time) STTS(space-time-time-space)

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Circuit Switching(cont’d)TST switch

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14.2 Packet Switching

~ data are transmitted in discrete units of potentially variable length blocks cabled packets.

Packet switching approaches

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Packet Switching(cont’d)Datagram Approach

~ each packet is treated independently from all others (datagram)

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Packet Switching(cont’d)Multiple channels in datagram approach

~ packets can be carried simultaneously by either TDM or FDM multiplexing

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Packet Switching(cont’d)

Virtual Circuit Approach~ A single route is chosen between sender and

receiver at the beginning of the session

SVC(Switched Virtual Circuit) PVC(Permanent Virtual Circuit)

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Packet Switching(cont’d)SVC(Switched Virtual Circuit)

~ is comparable conceptually to dial-up circuit switching

a. b.

c.

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Packet Switching(cont’d)

PVC(Permanent Virtual Circuit)~ is comparable to leased lines same virtual circuit is provided between two users

on a continuous basis circuit is dedicated to the specific user two PVC user always get the same route

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14.3 Message Switching~ is best known by the descriptive term store an

d forward

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14.4 Network Layer

~ is responsible for establishing, managing, and termination connections between physical network

protocols at this layer provide transparent routing and relaying services between networks

OSI model support two type of protocol : CONS and CLNS

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Network Layer(cont’d)CONS(Connection-Oriented Network Service)

~ establishes a virtual circuit for the transmission of data that is active for the entire transmission

process sender transmit a connection-request packet receiver acknowledge with a connection-confirm packet sender transmit data sender transmit a disconnect-request packet receiver acknowledge with a disconnect-confirm packet

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Network Layer(cont’d)

CLNS(Connection less Network Service)~ each packet of a multipacket transmission is

treated as an independent unit process

~ is simpler than that of a CONS

Sender transmit data