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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)

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Control plane: Routing protocol exchanges+ routing table precomputation

IV

IIII

II

Dest. Next hop

III-* IVDest. Next hop

III-* III

Dest. Next hop

III-B III-BIII-C 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

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1 1

4

1

Routing table(will have other entries)

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Control plane: Signaling Call setup

Host I-A Host

III-B

I

IV

III

II

ab

c

a

b

cd

a

b

Connection setup (Destination: III-B; Bandwidth: OC1; Timeslot: a, 1)

Dest. Next hop

III-* IV

Routingtable

Connection setup actions at each switch on the path:1. Parse message to extract parameter values2. Lookup routing table for next hop to reach destination3. Read and update CAC (Connection Admission Control) table4. Select timeslots on output port5. Configure switch fabric: write entry into timeslot mapping

table6. Construct setup message to send to next hop

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Call setup contd.

Connection setup actions at each switch on the path:1. Parse message to extract parameter values2. Lookup routing table for next hop to reach destination3. Read and update CAC (Connection Admission Control) table4. Select timeslots on output port5. Configure switch fabric: write entry into timeslot mapping table6. Construct setup message to send to next hop

Host I-A Host

III-B

I

IV

III

II

a

b

c

a

b

cd

a

b

Dest. Next hop

III-* IV

Routingtable

Next hopInterface (Port);

Capacity; Avail timeslots

IV c; OC3; 1, 3

CACtable

Connection setup (Destination: III-B; Bandwidth: OC1; Timeslot: a, 1)

INPUTPort /Timeslot

OUTPUTPort/Timeslot

a/1 c/3

Timeslotmapping table

Connection setup

Update to remove timeslot 3from available list

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Call setup contd.

Host I-A Host

III-B

I

IV

III

II

Connection setup

a

b

c

a

b

cd

ab

INPUTPort /Timeslot

OUTPUTPort/Timeslot

a/3 c/2

Perform same set of 6 connection setup steps at switch IV write timeslot mapping table entry, update CAC table andsend connection setup message to the next hop

Connection setup(Destination: III-B; Bandwidth: OC1;

Timeslot: a, 3)say, timeslot 2 was freeon interface cOutput 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

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Call setup contd.

Host I-A Host

III-B

I

IV

III

II

a

b

c

a

b

cd

a

b

INPUTPort /Timeslot

OUTPUTPort/Timeslot

d/2 b/1

Connectionsetup

Circuit setupcomplete

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

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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

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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

bc d

a

b

OUTPort/Timeslot

INPort /Timeslot

a/1 c/3IN

Port /TimeslotOUT

Port/Timeslot

a/3 c/2

INPort /Timeslot

OUTPort/Timeslot

d/2 b/1

1 2 3

1 2 31 2 3

1 2 3

In this example, what is the assumed data rate of the four links through which the circuit is routed?

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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

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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?

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Outline check

• Circuit switch– Routing

– Signaling

Difference in use of addresses

• Examples used in practice

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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

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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)

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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)

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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

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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