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Circuit Switching

Circuit Switching. Outline Types of switches Add multiplexers and demultiplexers TDM circuit switch Practice: SONET switch. Malathi Veeraraghavan University of Virginia. Some figures: Courtesy of Leon-Garcia & Widjaja’s textbook web site. Types of switches.

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Circuit Switching

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  1. Circuit Switching • Outline • Types of switches • Add multiplexers and demultiplexers • TDM circuit switch • Practice: SONET switch Malathi Veeraraghavan University of Virginia Some figures: Courtesy of Leon-Garcia & Widjaja’s textbook web site

  2. Types of switches • Routing: Required in controller for all three types of switches • Signaling: Admission control – hence required only for connection-oriented switches

  3. Types of switches • The type of switch is determined by the type of multiplexing used on its links • Circuit switch: • Position-based multiplexing • Time/Frequency/Wavelength Division Multiplexing • TDM, FDM, WDM: Term WDM is used for optical range • Packet switch: • Packet-based multiplexing

  4. Recall Time Division Multiplexing Example: 12 OC1 signals multiplexed on to an OC12 signal 1 2 . . 2 1 12 12 ........... 90 x 9 x 8 bits every 125s RATE: 51.84Mbps - OC1 12 x 90 x 9 x 8 bits every 125s RATE: 622.08 - OC12

  5. Example of a circuit switch (TDM): SONET Routing and signaling Controller OC1 OC1 OC12 OC12 PxP space switch (also called switch fabric or interconnection fabric) 1 1 . . . . . . . . OC12 OC12 2 2 . . . . . . . . . . . . . . . . OC12 OC12 Q Q . . . . . . . . demultiplexers multiplexers Crossconnect rate: OC1 What is the relation between P and Q? Answer: ?

  6. Example of a circuit switch: a SONET switch Endpoint A Endpoint C OC3 Ports or interfaces OC3 SONET switch a c b d OC3 Endpoint B OC3 Endpoint D Create a bidirectional OC1 circuit between host A and host C Use it for application 1 (leased-line from one customer) Create another bidirectional OC1 circuit between host A and host B Use it for application 2 (leased-line from another customer)

  7. Example of what happens inside a SONET switch (crossbar assumed) Controller 125ms OC1 Endpoint A A1 A2 a B1 Endpoint B b C1 c Endpoint C d Endpoint D OC3 a b c d Input ports Output ports B1 EP D EP A EP B EP C A1 A2 C1

  8. Timeslot mapping table • We need to use timeslot 2 on port a to/from host A for the AB OC1 circuit since timeslot 1 on this port was already used for the AC OC1 circuit

  9. “Unfolded” View of Switch Input line card functions Position-based demultiplexing Output line card functions Position-based multiplexing Space switch Close crosspoints when a circuit is setup Transfer data bits between line cards Open crosspoints when a circuit is released Controller Circuit setup/release phases Next lecture Line card Line card Line card Line card Circuit switch: position based Controller 1 Line card 1 2 2 Line card 3 3 Line card Space switch … … … … Q Q Line card Input ports Output ports Folded view: 1 line card has both input and output functions Data path Control path (a)

  10. Analogy for a circuit-switched network

  11. Analogy for "position based" multiplexing Think of Metro Center as a circuit switch If trains run exactly on time, the switching action of which train (red line, orange line) to direct to which outgoing track would be time-dependent http://www.wmata.com

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