Circuit Switching and Telephone Network

8장 Circuit Switching and 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.

Switching(cont’d) Switching method

8.1 Circuit Switching ~ create a direct physical connection between two devices such as phones or computer. Circuit-switched network

Circuit Switching(cont’d) 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(cont’d) ~ can use either two technologies. Switching

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.

Circuit Switching(cont’d) Crossbar switch

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

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

Circuit Switching(cont’d) Multiple paths

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

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.

Circuit Switching(cont’d) Time-division multiplexing without a time-slot interchange(TSI)

Circuit Switching(cont’d) Time-division multiplexing with a time-slot interchange(TSI)

Circuit Switching(cont’d) TSI 동작과정

Circuit Switching(cont’d) TDM Bus

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)

Circuit Switching(cont’d) TST switch

8.2 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

Telephone Network (cont’d) 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.

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

Telephone Network (cont’d) - POPs

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).

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