Transcript Chapter 4 Lecture Presentation

Circuit Switching
Malathi Veeraraghavan
University of Virginia
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Outline
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
Types of switches
Add multiplexers and demultiplexers
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
TDM circuit switch
Practice: SONET switch
Some figures: Courtesy of Leon-Garcia & Widjaja’s textbook web site
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Types of switches
Line card Circuit-switch (CS)
(multiplexing) (position-based)
Packet-switch (PS)
(header-based)
Controller
(admission
control or not)
Connectionless (CL)
(no admission control)
Connection-oriented (CO)
(admission control)
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e.g., IP routers; Ethernet
switches
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
Types of switches
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The type of switch is determined by the
type of multiplexing used on its links
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Circuit switch:
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Position-based multiplexing
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Time/Frequency/Wavelength Division Multiplexing
TDM, FDM, WDM: Term WDM is used for optical range
Packet switch:
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Packet-based multiplexing
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Recall Time Division Multiplexing
Example: 12 OC1 signals multiplexed on to an OC12 signal
1
2
.
.
12
1
2
12
...........
90 x 9 x 8 bits
every 125s
12 x 90 x 9 x 8 bits
every 125s
RATE: 51.84Mbps - OC1
RATE: 622.08 - OC12
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Example of a circuit switch (TDM): SONET
Controller
1
OC12
2
..
..
..
..
.
.
.
.
OC12
OC1
OC1
OC12
Q
..
..
Routing and
signaling
..
..
PxP
space
switch
(also called
switch fabric
or
interconnection
fabric)
OC12
1
OC12
..
..
..
..
demultiplexers
Crossconnect rate: OC1
What is the relation between P and Q? Answer: ?
2
Q
.
.
.
.
OC12
multiplexers
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Example of a circuit switch: a SONET switch
Endpoint A
OC3
Ports
or interfaces
a
b
Endpoint B
OC3
SONET
switch
OC3
Endpoint C
c
d
OC3
Endpoint D
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)
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Example of what happens inside a
SONET switch (crossbar assumed)
Controller
125s
Endpoint
A
Endpoint
B
OC1
A2 A1
a
B1
b
C1
Endpoint
C
c
Endpoint
D
d
OC3
a
Input ports
b
c
d
EP B
EP C
A1
EP A
A2
C1 B1
Output ports
EP D
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Timeslot mapping table
Input
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Output
Port
Timeslot Port
Timeslot
a
c
1
1
c
a
1
1
a
b
2
1
b
a
1
2
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
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Circuit switch: position based
“Unfolded” View of Switch
 Input line card functions
Controller

Q
Line card
Line card
2
Line card
3
Line card
Line card
Line card

Q
Position-based demultiplexing
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Position-based multiplexing
Output line card functions
Space switch
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
…
1
…
…
3
Line card
Space switch
2
Line card
…
1
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Controller
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Input ports
Data path
Control path
Close crosspoints when a
circuit is setup
Transfer data bits between
line cards
Open crosspoints when a
circuit is released
Circuit setup/release phases
Next lecture
Output ports
(a)
Folded view: 1 line card has
both input and output functions
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Analogy for a circuit-switched
network
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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
http://www.wmata.com
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