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 Line card (multiplexing) Controller (admission control or not) Circuit-switch (CS) (position-based) Packet-switch (PS) (header-based) Connectionless (CL) (no admission control) e.g., IP routers; Ethernet switches Connection-oriented (CO) (admission control) e.g., telephone network circuit switches, SONET switches Virtual-circuit 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 x 9 x 8 bits every 125  s RATE: 51.84Mbps - OC x 90 x 9 x 8 bits every 125  s RATE: OC12 Example: 12 OC1 signals multiplexed on to an OC12 signal

5 Example of a circuit switch (TDM): SONET 11 2 Q 2 Q demultiplexersmultiplexers OC12 OC1 Crossconnect rate: OC1 Controller Routing and signaling What is the relation between P and Q? Answer: ? PxP space switch (also called switch fabric or interconnection fabric)

6 Example of a circuit switch: a SONET switch Endpoint A Endpoint D Endpoint B SONET switch a b c d OC3 Endpoint C 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) Ports or interfaces

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

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 InputOutput PortTimeslotPortTimeslot a1c1 c1a1 a2b1 b1a2

9 Controller Q Line card Space switch Line card Q Input portsOutput ports Data path Control path (a) … … … … Circuit switch: position based “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 Folded view: 1 line card has both input and output functions

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