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Kyung Hee University

Prof. Choong Seon HONG

SwitchingSwitching

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1414 장 장 SWITCHING : A NETWORK LAYER FUNCTIONSWITCHING : A NETWORK LAYER FUNCTION

14.1 회선교환 (Circuit Switching)

14.2 패킷 교환 (Packet Switching)

14.3 메시지 교환 (Message Switching)

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Switching(cont’d)Switching(cont’d)

Switching

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

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Switching(cont’d)Switching(cont’d)

Switching method

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14.1 Circuit Switching14.1 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(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)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(cont’d)

Circuit Switching

~ can use either two technologies.

Switching

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Circuit Switching(cont’d)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)Circuit Switching(cont’d)

Crossbar switch

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Circuit Switching(cont’d)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 crosspoints are in use at a given time.

the rest are idle

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Circuit Switching(cont’d)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)Circuit Switching(cont’d)

Multiple paths

a. b.

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Circuit Switching(cont’d)Circuit Switching(cont’d)

Blocking

~ 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)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)Circuit Switching(cont’d)

Time-division multiplexing, without and with a time-slot

interchange(TSI)

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Circuit Switching(cont’d)Circuit Switching(cont’d)

Time-division multiplexing, without and with a time-slot

interchange(TSI)

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Circuit Switching(cont’d)Circuit Switching(cont’d)

TSI 동작과정

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Circuit Switching(cont’d)Circuit Switching(cont’d)

TDM Bus

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Circuit Switching(cont’d)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)Circuit Switching(cont’d)

TST switch

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Circuit Switching(cont’d)Circuit Switching(cont’d)

PSTN Hierarchy

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Circuit Switching(cont’d)Circuit Switching(cont’d)

Touch-Tone Dialing

For example, the number, two bursts of analog signals with frequencies 852 and 1336 Hz are sent to the end office

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14.2 Packet Switching14.2 Packet Switching

~ data are transmitted in discrete units of potentially vari

able length blocks of packets.

Packet switching approaches

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Packet Switching(cont’d)Packet Switching(cont’d)Datagram Approach

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

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Packet Switching(cont’d)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)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)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)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 users always get the same route

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Packet Switching(cont’d)Packet Switching(cont’d)

PVC

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Packet Switching(cont’d)Packet Switching(cont’d)

Dedicated versus shared

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Packet Switching(cont’d)Packet Switching(cont’d)

Path versus route

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14.3 Message Switching14.3 Message Switching

is best known by the descriptive term store and forward