1. Chapter 8 Circuit Switching and Telephone Network

2. 8장 Circuit Switching and Telephone Network

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

4. Switching(cont’d)
Switching method

5. 8.1 Circuit Switching
~ create a direct physical connection between two devices such as phones or computer.
Circuit-switched network

6. 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

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

8. 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.

9. Circuit Switching(cont’d)
Crossbar switch

10. 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

11. 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

12. Circuit Switching(cont’d)
Multiple paths

13. 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

14. 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.

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

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

17. Circuit Switching(cont’d)
TSI 동작과정

18. Circuit Switching(cont’d)
TDM Bus

19. 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

20. Telephone Network (cont’d)

21. 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).

22. 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