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# Circuit Switching and Telephone Network - PowerPoint PPT Presentation

Circuit Switching and Telephone Network. 8 장 Circuit Switching and Telephone Network. 8.1 회선교환 (Circuit Switching) 8.2 전화망 (Telephone Network). Switching. 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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### Circuit Switching andTelephone Network

8장 Circuit Switching and Telephone Network

8.1 회선교환(Circuit Switching)

8.2 전화망 (Telephone Network)

• Switching

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

• Switching method

~ create a direct physical connection between two devices such as phones or computer.

• Circuit-switched network

• 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

• Circuit Switching

~ can use either two technologies.

• Switching

• 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.

• Crossbar switch

• 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

• 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

• Multiple paths

• 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

• 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.

• Time-division multiplexing without a time-slot interchange(TSI)

• Time-division multiplexing with a time-slot interchange(TSI)

• TSI 동작과정

• TDM Bus

• 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)

• TST switch

• 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

• Intra-LATA (local access transport area) services are provided by local exchange carriers. Since 1996, there are two types of LECs (local exchange carriers): incumbent local exchange carriers and competitive local exchange carriers.

• 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

• 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).

• 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