1 Kyung Hee University Prof. Choong Seon HONG Switching.
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1414 장 장 SWITCHING : A NETWORK LAYER FUNCTIONSWITCHING : A NETWORK LAYER FUNCTION
14.1 회선교환 (Circuit Switching)
14.2 패킷 교환 (Packet Switching)
14.3 메시지 교환 (Message Switching)
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Switching(cont’d)Switching(cont’d)
Switching
~ whenever we have multiple devices, we have the problem the problem of how to connect them to make one-to-one communication possible.
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14.1 Circuit Switching14.1 Circuit Switching
~ create a direct physical connection between two
devices such as phones or computer.
Circuit-switched network
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Circuit Switching
~ is a device with n inputs and m outputs that creates a temporary connection between an input link and output link.
A circuit switch
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Circuit Switching(cont’d)Circuit Switching(cont’d)
n-by-n folded switch can connect n lines in full-duplex
mode
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Circuit Switching
~ can use either two technologies.
Switching
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Space-Division Switches
the paths in the circuit are separated from each other spatially(crossbar switch)
Crossbar switch
~ connect n input to m output in a grid, using electronic microswitch(transistor) at each crosspoint.
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Limitation of crossbar switch
The number of switch(huge size)
: connect n inputs by m output
require n * m crosspoint.
(ex : 1000 input, 1000 output → 1,000,000 crosspoint)
inefficient
fewer than 25% of the crosspoints are in use at a given time.
the rest are idle
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Multistage Switches
Devices are linked to switches that, in turn are linked to a hierarchy of other switches
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Blocking
~ compare the number of crosspoints in a 15-by-15 single-stage crossbar switch with the 15-by-15 multistage switch.
single-stage switch
need 225 crosspoint(15 * 15)
multistage switch
first-stage : 10 crosspoint(5 * 2) *3 = 30 crosspoint second-stage : 9 crosspoint(3 *3) * 2 = 18 crosspoint third-stage : 10 crosspoint(5 * 2) *3 = 30 crosspoint
total number of crosspoint : 78
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Time-Division Switch
~ is accomplished using TDM(Time-division multiplexing) and TSI(Time-Slot Interchange)
TSI - change the ordering of the slots based on the desired connections.
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Time-division multiplexing, without and with a time-slot
interchange(TSI)
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Time-division multiplexing, without and with a time-slot
interchange(TSI)
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Space-and Time-Division Switching Combinations
~ combine space-division and time-division technology to take advantage of the best of both
TST(time-space-time)
TSST(time-space-space-time)
STTS(space-time-time-space)
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Circuit Switching(cont’d)Circuit Switching(cont’d)
Touch-Tone Dialing
For example, the number, two bursts of analog signals with frequencies 852 and 1336 Hz are sent to the end office
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14.2 Packet Switching14.2 Packet Switching
~ data are transmitted in discrete units of potentially vari
able length blocks of packets.
Packet switching approaches
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Packet Switching(cont’d)Packet Switching(cont’d)Datagram Approach
~ each packet is treated independently from all others (datagram)
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Packet Switching(cont’d)Packet Switching(cont’d)
Multiple channels in datagram approach
~ packets can be carried simultaneously by either TDM or FDM multiplexing
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Packet Switching(cont’d)Packet Switching(cont’d)
Virtual Circuit Approach
~ A single route is chosen between sender and receiver at the beginning of the session
SVC(Switched Virtual Circuit)
PVC(Permanent Virtual Circuit)
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Packet Switching(cont’d)Packet Switching(cont’d)
SVC(Switched Virtual Circuit)
~ is comparable conceptually to dial-up circuit switching
a. b.
c.
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Packet Switching(cont’d)Packet Switching(cont’d)
PVC(Permanent Virtual Circuit)
~ is comparable to leased lines
same virtual circuit is provided between two users on a continuous basis
circuit is dedicated to the specific user
two PVC users always get the same route
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