1 Circuit switch controller: Routing and signaling Malathi Veeraraghavan University of Virginia Circuit switch –Routing –Signaling Difference in use of addresses Examples used in practice

2 A network of circuit switches Control plane –Switch controllers exchange routing information –Switch controllers exchange signaling messages to check if there is sufficient bandwidth to admit the call (call setup) and after use, release the bandwidth Data plane –Data frames carrying user data are switched from link to link across each switch based on their "positions" (time slots/wavelengths)

3 Control plane: Routing protocol exchanges + routing table precomputation IV I III II Dest.Next hop III-* IV Dest.Next hop III-* III Dest.Next hop III-B III-C Host I-A Host III-B Host III-C Similar to the routing protocol exchanges used in connectionless (CL) packet-switched networks More emphasis on exchanging loading information Routing table (will have other entries)

4 Control plane: Signaling Call setup Host I-A Host III-B I IV III II a b c a b c d a b Connection setup (Destination: III-B; Bandwidth: OC1; Timeslot: a, 1) Dest.Next hop III-* IV Routing table Connection setup actions at each switch on the path: 1.Parse message to extract parameter values 2.Lookup routing table for next hop to reach destination 3.Read and update CAC (Connection Admission Control) table 4.Select timeslots on output port 5.Configure switch fabric: write entry into timeslot mapping table 6.Construct setup message to send to next hop

5 Call setup contd. Connection setup actions at each switch on the path: 1.Parse message to extract parameter values 2.Lookup routing table for next hop to reach destination 3.Read and update CAC (Connection Admission Control) table 4.Select timeslots on output port 5.Configure switch fabric: write entry into timeslot mapping table 6.Construct setup message to send to next hop Host I-A Host III-B I IV III II a b c a b c d a b Dest.Next hop III-* IV Routing table Next hop Interface (Port); Capacity; Avail timeslots IV c; OC3; 1, 3 CAC table Connection setup (Destination: III-B; Bandwidth: OC1; Timeslot: a, 1) INPUT Port /Timeslot OUTPUT Port/Timeslot a/1 c/3 Timeslot mapping table Connection setup Update to remove timeslot 3 from available list

6 Call setup contd. Host I-A Host III-B I IV III II Connection setup a b c a b c d a b INPUT Port /Timeslot OUTPUT Port/Timeslot a/3 c/2 Perform same set of 6 connection setup steps at switch IV write timeslot mapping table entry, update CAC table and send connection setup message to the next hop Connection setup (Destination: III-B; Bandwidth: OC1; Timeslot: a, 3) say, timeslot 2 was free on interface c Output time slot assigned for a given circuit at a switch is the same as the input time slot assigned to that circuit at the next-hop

7 Call setup contd. Host I-A Host III-B I IV III II a b c a b c d a b INPUT Port /Timeslot OUTPUT Port/Timeslot d/2 b/1 Connection setup Circuit setup complete Perform same set of 6 connection setup steps at switch III Reverse setup-confirmation messages typically sent from destination through switches to source host Connection setup

8 Analogy Call setup: analogous to an airline passenger calling ahead to make reservations for a seat on each leg of a multi-flight trip Reserved time slots on each link: similar to seat assigments on each flight –just as seat assignments can change from flight-to-flight, so can the assigned time slot on the various links of the end-to-end circuit When trip actually starts and passenger arrives on one flight at an airport, he/she simply "moves" to assigned seat on next flight - next slide - user data forwarding

9 Data plane: User-data transfer Bits arriving at switch I on time slot 1 at port a are switched to time slot 3 of port c Host I-A Host III-B I IV III II a b c a b c d a b OUT Port/Timeslot IN Port /Timeslot a/1 c/3 IN Port /Timeslot OUT Port/Timeslot a/3 c/2 IN Port /Timeslot OUT Port/Timeslot d/2 b/ In this example, what is the assumed data rate of the four links through which the circuit is routed?

10 Release procedure When the communication session using the circuit ends, there is a hop-by-hop release procedure (similar to the setup procedure) to release timeslots (bandwidth) for the next call

11 Unidirectional vs. bidirectional circuits Was the circuit that was setup in the example a unidirectional circuit or a bidirectional circuit? Which step would need to change?

12 Outline check Circuit switch –Routing –Signaling  Difference in use of addresses Examples used in practice

13 Difference in use of addresses Where are addresses used: control plane or data plane? –In connectionless packet-switched networks, destination addresses are carried in packet headers Hence, data plane –In circuit-switched networks, these addresses are carried in call-setup signaling messages Hence, control plane

14 Examples used in practice Addressing –Ethernet switched network 6-byte MAC address –IP-based networks 4-byte IP addresses –Telephone networks 8-byte E.164 address (telephone number)

15 Examples used in practice Routing schemes –In Ethernet networks Address learning and the spanning tree algorithm –In the Internet: Open Path Shortest First (OSPF) Border Gateway Protocol (BGP) –In telephone networks: Real-Time Network Routing (RTNR)

16 Examples used in practice Signaling protocols –SS7 (Signaling System No. 7) used to set up and release DS0 (64kbps) circuits in a telephone (circuit-switched) network –Resource reSerVation Protocol with Traffic Engineering (RSVP-TE) used in optical circuit-switched networks such as SONET networks

17 Test your learning Network types Addresses used in data path or control path? Routing (place check mark if this function is needed) Signaling (place check mark if this function is needed) Connectionless packet switched Connection-oriented circuit switched