1. Chapter 8 Switching Switching at the physical layer in the traditional telephone network uses the circuit-switching approach.

2. Figure 8.2 Taxonomy of switched networks Figure 8.1 Switched network

3. CIRCUIT-SWITCHED NETWORKS A circuit-switched network consists of a set of switches connected by physical links. A connection between two stations is a dedicated path made of one or more links. However, each connection uses only one dedicated channel on each link. Each link is normally divided into n channels by using FDM or TDM. has three phases –Establish –Transfer –Disconnect inefficient –channel capacity dedicated for duration of connection –if no data, capacity wasted set up (connection) takes time once connected, transfer is transparent

4. Figure 8.3 A trivial circuit-switched network A circuit-switched network is made of a set of switches connected by physical links, in which each link is divided into n channels.

5. Public Circuit Switched Network Circuit Establishment

6. Packet Switching circuit switching was designed for voice packet switching was designed for data transmitted in small packets packets contains user data and control info –user data may be part of a larger message –control info includes routing (addressing) info packets are received, stored briefly (buffered) and past on to the next node In a packet-switched network, there is no resource reservation; resources are allocated on demand.

7. Packet Switching

8. Packet Switching Datagram Approach Packet Switching Virtual Circuit Approach

9. Blocking or Non-blocking blocking network –may be unable to connect stations because all paths are in use –used on voice systems non-blocking network –permits all stations to connect at once –used for some data connections

10. 8-4 STRUCTURE OF A SWITCH Figure 8.17 Crossbar switch with three inputs and four outputs

11. Circuit Switch Elements

12. Figure 8.18 Multistage switch In a three-stage switch, the total number of crosspoints is 2kN + k(N/n) 2 which is much smaller than the number of crosspoints in a single-stage switch (N 2 ).

13. Design a three-stage, 200 × 200 switch (N = 200) with k = 4 and n = 20. Solution In the first stage we have N/n or 10 crossbars, each of size 20 × 4. In the second stage, we have 4 crossbars, each of size 10 × 10. In the third stage, we have 10 crossbars, each of size 4 × 20. The total number of crosspoints is 2kN + k(N/n) 2, or 2000 crosspoints. This is 5 percent of the number of crosspoints in a single-stage switch (200 × 200 = 40,000). Example 8.3 According to the Clos criterion: n = (N/2) 1/2 k > 2n – 1 Crosspoints ≥ 4N [(2N) 1/2 – 1]

14. Redesign the previous three-stage, 200 × 200 switch, using the Clos criteria with a minimum number of crosspoints. Solution We let n = (200/2) 1/2, or n = 10. We calculate k = 2n − 1 = 19. In the first stage, we have 200/10, or 20, crossbars, each with 10 × 19 crosspoints. In the second stage, we have 19 crossbars, each with 10 × 10 crosspoints. In the third stage, we have 20 crossbars each with 19 × 10 crosspoints. The total number of crosspoints is 20(10 × 19) + 19(10 × 10) + 20(19 ×10) = 9500. Example 8.4

15. Figure 8.19 Time-slot interchange modern digital systems use intelligent control of space & time division elements use digital time division techniques to set up and maintain virtual circuits partition low speed bit stream into pieces that share higher speed stream individual pieces manipulated by control logic to flow from input to output Time Division Switching

16. Figure 8.20 Time-space-time switch

17. Figure 8.21 Packet switch components

18. Figure 8.22 Input port Figure 8.23 Output port

19. Figure 8.24 A banyan switch

20. Figure 8.25 Examples of routing in a banyan switch

21. Figure 8.26 Batcher-banyan switch

22. In Channel Signaling Use same channel for signaling and call –Requires no additional transmission facilities Inband –Uses same frequencies as voice signal –Can go anywhere a voice signal can –Impossible to set up a call on a faulty speech path Out of band –Voice signals do not use full 4kHz bandwidth –Narrow signal band within 4kHz used for control –Can be sent whether or not voice signals are present –Need extra electronics –Slower signal rate (narrow bandwidth)

23. Drawbacks of In Channel Signaling Limited transfer rate Delay between entering address (dialing) and connection Overcome by use of common channel signaling

24. Common Channel Signaling Control signals carried over paths independent of voice channel One control signal channel can carry signals for a number of subscriber channels Common control channel for these subscriber lines Associated Mode –Common channel closely tracks interswitch trunks Disassociated Mode –Additional nodes (signal transfer points) –Effectively two separate networks

25. Common v. In Channel Signaling

26. Common Channel Signaling Modes