1 kyung hee university circuit switching and telephone network

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Circuit Switching andCircuit Switching andTelephone NetworkTelephone Network

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88 장 장 Circuit Switching and Telephone NetworkCircuit Switching and Telephone Network

8.1 회선교환 (Circuit Switching)

8.2 전화망 (Telephone Network)

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SwitchingSwitching

Switching

~ whenever we have multiple devices, we have 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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8.1 Circuit Switching8.1 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 Switch

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)

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

Combines crossbar switches in several stages

Provides multiple paths connecting each pair of linked devices

Reduction in crosspoints results in blocking during heavy traffic

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

Multiple paths

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

Crosspoint

~ 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 a time-slot

interchange(TSI)

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

Time-division multiplexing 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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8.2 Telephone Network8.2 Telephone Network

Major Components

• local loop connects subscriber to nearest end office, 1st 3 digits of phone number define the office, next four define the local loop number

• trunks are the transmission media handling the communication between offices

• switching office has switches that connects several local loops or trunks

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Telephone Network (cont’d)Telephone Network (cont’d)

Intra-LATA (local access transport area) services are pr

ovided by local exchange carriers. Since 1996, there are

two types of LECs (local exchange carriers): incumbent

local exchange carriers and competitive local exchange

carriers.

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Telephone Network (cont’d)Telephone Network (cont’d)

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Telephone Network (cont’d)Telephone Network (cont’d)

IXCs are interexchange carriers (long-distance companies)

POPs are points of presence – a switching office in a LATA

that allows an IXC to provide inter-LATA services

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Telephone Network (cont’d) - POPsTelephone Network (cont’d) - POPs

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Telephone Network (cont’d)Telephone Network (cont’d)

Voice communication used analog signals in the past,

but is now moving to digital signals. On the other hand,

dialing started with digital signals (rotary) and is now

moving to analog signals (touch-tone).

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

Touch-Tone Dialing

When a user dials, for example, the number 8, two bursts of analog signals with frequencies 852 and 1336 Hz are sent to the end office