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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. A network of circuit switches. Control plane Switch controllers exchange routing information

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circuit switch controller routing and signaling
Circuit switch controller:Routing and signaling

Malathi Veeraraghavan

University of Virginia

  • Circuit switch
    • Routing
    • Signaling
  • Difference in use of addresses
  • Examples used in practice
a network of circuit switches
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)
control plane routing protocol exchanges routing table precomputation

Dest.

Next hop

III-B

III-B

III-C

III-C

Dest.

Next hop

III-*

III

Control plane: Routing protocol exchanges+ routing table precomputation
  • Similar to the routing protocol exchanges used in connectionless (CL) packet-switched networks
  • More emphasis on exchanging loading information

II

4

5

1

Host I-A

Host III-B

I

III

1

1

IV

Host III-C

Dest.

Next hop

III-*

IV

Routing table

(will have other entries)

control plane signaling call setup
Control plane: Signaling Call setup

Connection setup (Destination: III-B;

Bandwidth: OC1;

Timeslot: a, 1)

Connection setup actions at each switch on the path:

  • Parse message to extract parameter values
  • Lookup routing table for next hop to reach destination
  • Read and update CAC (Connection Admission Control) table
  • Select timeslots on output port
  • Configure switch fabric: write entry into timeslot mapping table
  • Construct setup message to send to next hop

II

a

b

Host I-A

a

III

b

I

Host III-B

c

b

d

c

IV

a

Dest.

Next hop

Routing

table

III-*

IV

call setup contd
Call setup contd.

Connection setup (Destination: III-B;

Bandwidth: OC1;

Timeslot: a, 1)

Connection setup actions at each switch on the path:

  • Parse message to extract parameter values
  • Lookup routing table for next hop to reach destination
  • Read and update CAC (Connection Admission Control) table
  • Select timeslots on output port
  • Configure switch fabric: write entry into timeslot mapping table
  • Construct setup message to send to next hop

II

b

a

Host I-A

a

b

III

I

Connection setup

Host III-B

c

b

d

c

IV

a

Dest.

Next hop

Routing

table

III-*

IV

Interface (Port);

Capacity; Avail timeslots

CAC

table

Next hop

c; OC3; 1, 3

IV

INPUT

Port /Timeslot

OUTPUT

Port/Timeslot

Timeslot

mapping table

a/1

c/3

Update to remove timeslot 3

from available list

call setup contd1
Call setup contd.

II

b

a

b

Host I-A

a

Connection setup

III

I

c

Host III-B

b

d

c

IV

a

Connection setup

(Destination: III-B;

Bandwidth: OC1;

Timeslot: a, 3)

INPUT

Port /Timeslot

OUTPUT

Port/Timeslot

say, timeslot 2 was free

on interface c

a/3

c/2

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

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

call setup contd2
Call setup contd.

INPUT

Port /Timeslot

OUTPUT

Port/Timeslot

II

d/2

b/1

b

a

Host I-A

a

Connection setup

III

I

Host III-B

b

c

b

d

c

IV

a

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

analogy
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
data plane user data transfer
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

IN

Port /Timeslot

OUT

Port/Timeslot

1

2

3

II

d/2

b/1

1

2

3

b

a

1

2

3

Host I-A

a

III

I

Host III-B

b

c

1

2

3

b

d

c

IV

a

IN

Port /Timeslot

OUT

Port/Timeslot

IN

Port /Timeslot

OUT

Port/Timeslot

a/1

c/3

a/3

c/2

In this example, what is the assumed data rate of the four links

through which the circuit is routed?

release procedure
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
unidirectional vs bidirectional circuits
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?
outline check
Outline check
  • Circuit switch
    • Routing
    • Signaling
  • Difference in use of addresses
  • Examples used in practice
difference in use of addresses
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
examples used in practice
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)
examples used in practice1
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)
examples used in practice2
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