1. DATA COMMUNICATION (ELA…) CIRCUIT SWITCHING AND PACKET SWITCHING 1

2. S WITCHED N ETWORK

3. N ODES  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  have two different switching technologies circuit switching packet switching

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

5. P UBLIC C IRCUIT S WITCHED N ETWORK

6. C IRCUIT E STABLISHMENT

7. C IRCUIT S WITCH E LEMENTS

8. B LOCKING OR N ON - 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 (in pair) at once used for some data connections

9. S PACE D IVISION S WITCH

10. 3 S TAGE S PACE D IVISION S WITCH

11. T IME D IVISION S WITCHING  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. T IME S LOT I NTERCHANGE  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. T RADITIONAL C IRCUIT S WITCHING

14. S OFTSWITCH

15. P ACKET S WITCHING  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 control info includes routing (addressing) info  packets are received, stored briefly (buffered) and passed on to the next node

16. P ACKET S WITCHING

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

18. P ACKET S WITCHING T ECHNIQUES  station breaks long message into packets  packets sent one at a time to the network  packets can be handled in two ways datagram virtual circuit

19. D ATAGRAM D IAGRAM

20. V IRTUAL C IRCUIT D IAGRAM

21. V IRTUAL C IRCUITS V D ATAGRAM  virtual circuits network can provide sequencing and error control packets are forwarded more quickly less reliable  datagram No setup phase more flexible more reliable

22. P ACKET S IZE

23. C IRCUIT V P ACKET S WITCHING  performance depends on various delays propagation delay - negligible transmission time node delay – processing time  range of other characteristics, including: Network size & topology Load pattern

24. E VENT T IMING

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. S UMMARY  circuit verses packet switching network approaches