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Data and Computer Communications

Learn about circuit switching and packet switching in wide area networks, including setup phases, connection types, time division elements, and advantages of packet switching. Understand the differences in switching techniques and network designs.

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Data and Computer Communications

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  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 • have two different switching technologies • circuit 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 • 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. 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 • used on voice systems • non-blocking network • permits all stations to connect (in pair) at once • 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 • 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 • 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. 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 • virtual circuit

  19. DatagramDiagram

  20. VirtualCircuitDiagram

  21. Virtual Circuits v Datagram • 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. Packet Size

  23. Circuit v Packet Switching • 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. 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 1st hop, Packet data = 1024 -16 =1008 • D2 = D3 = D4 = (Tr. + Prop. Time) of the last frame over 2nd, 3rd, and 4th hops.

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

  28. Summary • circuit verses packet switching network approaches

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