Transcript routing-sig - University of Virginia

Circuit switch controller:
Routing and signaling
Malathi Veeraraghavan
University of Virginia
• Circuit switch
– Routing
– Signaling
• Difference in use of addresses
• Examples used in practice
1
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)
2
Control plane: Routing protocol exchanges
+ routing table precomputation
II
4
5
Dest.
Next hop
III-B
III-C
III-B
III-C
1
Host
I-A
I
III
1
Dest.
Next hop
III-*
IV
Routing table
(will have other entries)
1
IV
Host
III-B
Host
III-C
Dest.
Next hop
III-*
III
• Similar to the routing protocol exchanges used in
connectionless (CL) packet-switched networks
• More emphasis on exchanging loading information
3
Control plane: Signaling
Call setup
Connection setup
(Destination: III-B;
Bandwidth: OC1;
Timeslot: a, 1)
II
a
b
Host
I-A
a
I
III
c
b
c
Routing
table
Dest.
Next hop
III-*
IV
b
d
Host
III-B
IV
a
Connection setup actions at each switch on the path:
1.
2.
3.
4.
5.
6.
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
4
Call setup contd.
Connection setup
(Destination: III-B;
Bandwidth: OC1;
Timeslot: a, 1)
II
b
a
a
Host
I-A
I
Connection
setup
b
c
III
c
Routing
table
CAC
table
Dest.
Next hop
III-*
IV
a
Interface (Port);
Next hop Capacity; Avail timeslots
c; OC3; 1, 3
IV
Timeslot
mapping table
INPUT
Port /Timeslot
a/1
OUTPUT
Port/Timeslot
b
d
Host
III-B
IV
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
c/3
Update to remove timeslot 3
from available list
5
Call setup contd.
II
b
Host
I-A
a
a
I
c
b
Connection
setup
III
b
Host
III-B
d
c
Connection setup
(Destination: III-B;
Bandwidth: OC1;
Timeslot: a, 3)
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
IV
a
INPUT
OUTPUT
Port /Timeslot Port/Timeslot
a/3
c/2
say, timeslot 2 was free
on interface c
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
6
Call setup contd.
INPUT
OUTPUT
Port /Timeslot Port/Timeslot
II
d/2
b
Host
I-A
b/1
a
a
I
c
b
Connection
setup
c
a
III
Host
III-B
b
d
IV
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
7
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
8
Data plane: User-data transfer
IN
OUT
Port /Timeslot Port/Timeslot
12 3
II
b
Host
I-A
d/2
12 3
a
12 3
a
I
c
b
a
a/1
c/3
b
12 3
Host
III-B
IV
IN
OUT
Port /Timeslot Port/Timeslot
a/3
•
III
d
c
IN
OUT
Port /Timeslot Port/Timeslot
b/1
c/2
Bits arriving at switch I on time slot 1 at port a are switched to time slot 3 of port c
In this example, what is the assumed data rate of the four links
through which the circuit is routed?
9
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
10
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?
11
Outline check
• Circuit switch
– Routing
– Signaling
 Difference in use of addresses
• Examples used in practice
12
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
13
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)
14
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)
15
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
16
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
17