1. Data and Computer Communications Chapter 10 – Circuit Switching and Packet Switching (Wide Area Networks)

2. Switched Network

3. Nodes  a collection of switching nodes and connections is a communications network  nodes may connect to other nodes only, or to stations and other nodes  network is usually partially connected some redundant connections are desirable some redundant connections are desirable  have two different switching technologies circuit switching circuit switching packet switching packet switching

4. Circuit Switching  uses a dedicated path between two stations  has three phases Establish - an end-to-end (station-to-station) circuit Establish - an end-to-end (station-to-station) circuit Transfer – Data transmitted through the network Transfer – Data transmitted through the network Disconnect - the connection is terminated, usually by of one of the two stations Disconnect - the connection is terminated, usually by of one of the two stations  inefficient channel capacity is dedicated for duration of connection channel capacity is dedicated for duration of connection if no data, capacity wasted (Client / server) if no data, capacity wasted (Client / server)  set up (connection) takes time  once connected, transfer is transparent (no delay)

5. Public Circuit Switched Network

6. Circuit Establishment

7. Circuit Switch Elements

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

9. Space Division Switch

10. 3 Stage Space Division Switch

11. Time Division Switching  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

12. Time Slot Interchange  TSI receives input in sequence, but sends them to the output out-of sequence (as needed by the devices)  Stored in memory, and scanned out  Delivery of data is delayed  # How many cross points are needed for a crossbar switch to connect 1000 telephones?

13. Traditional Circuit Switching

14. Softswitch

15. Packet Switching  circuit switching was designed for voice  packet switching was designed for data  transmitted in small packets (1000 octets)  packets contain user data and control info user data may be part of a larger message user data may be part of a larger message control info includes routing (addressing) info control info includes routing (addressing) info  packets are received, stored briefly (buffered) and passed on to the next node

16. Packet Switching

17. Advantages  line efficiency single link shared by many packets over time single link shared by many packets over time packets queued and transmitted as fast as possible packets queued and transmitted as fast as possible  data rate conversion stations connects to local node at own speed stations connects to local node at own speed nodes buffer data if required to equalize rates nodes buffer data if required to equalize rates  packets accepted even when network is busy  priorities can be used

18. Packet Switching Techniques  station breaks long message into packets  packets sent one at a time to the network  packets can be handled in two ways datagram datagram virtual circuit virtual circuit

19. Datagram Diagram

20. Virtual Circuit Diagram

21. Virtual Circuits v Datagram  virtual circuits network can provide sequencing and error control network can provide sequencing and error control packets are forwarded more quickly packets are forwarded more quickly less reliable less reliable  datagram No setup phase No setup phase more flexible more flexible more reliable more reliable

22. Packet Size

23. Circuit v Packet Switching  performance depends on various delays propagation delay - negligible propagation delay - negligible transmission time transmission time node delay – processing time node delay – processing time  range of other characteristics, including: Network size & topology Network size & topology Load pattern Load pattern

24. Event Timing

25.  # N = hops = 4, L = message length = 3200 bits, B = data rate = 9600, P = packet (data + overhead) size = 1024 bits, H = overhead = 16 bits, S = call set up time = 0.2 s, D = propagation delay / hop = 0.001 s. (ignore the time for ACK in circuit switching and virtual circuit packet switching)  Find end to end delay for circuit switching, datagram and virtual circuit packet switching.

26.  Circuit:  T = C1 + C2  C1 = S, C2 = Tr. + Prop. Time  Datagram:  T = D1 + D2 + D3 + D4  D1 = (Tr. + Prop. Time) of all packets over 1 st hop, Packet data = 1024 -16 =1008  D2 = D3 = D4 = (Tr. + Prop. Time) of the last frame over 2 nd, 3 rd, and 4 th hops.

27.  Virtual:  T = V1 + V2  V1 = S, V2 = Datagram T

28. Summary  circuit verses packet switching network approaches