1 14 장 switching : a network layer function 14.1 회선교환 (circuit switching) 14.2 패킷...
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14 장 SWITCHING :A NETWORK LAYER FUNCTION
14.1 회선교환 (Circuit Switching)
14.2 패킷 교환 (Packet Switching)
14.3 메시지 교환 (Message Switching)
14.4 네트워크층
14.5 요약
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Switching(cont’d)Switching
~ whenever we have multiple devices, we have the problem the problem of how to connect them to make one-one-one communication possible.
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14.1 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
~ 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)
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)
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 crosspoint are in use at a given time.
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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)Block
~ 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)
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)
Time-division multiplexing, without and with a time-slot interchange(TSI) - No switching
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Circuit Switching(cont’d)
Time-division multiplexing, without and with a time-slot interchange(TSI) - Switching
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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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14.2 Packet Switching
~ data are transmitted in discrete units of potentially variable length blocks cabled packets.
Packet switching approaches
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Packet Switching(cont’d)Datagram Approach
~ each packet is treated independently from all others (datagram)
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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)
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)SVC(Switched Virtual Circuit)
~ is comparable conceptually to dial-up circuit switching
a. b.
c.
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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 user always get the same route
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14.4 Network Layer
~ is responsible for establishing, managing, and termination connections between physical network
protocols at this layer provide transparent routing and relaying services between networks
OSI model support two type of protocol : CONS and CLNS
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Network Layer(cont’d)CONS(Connection-Oriented Network Service)
~ establishes a virtual circuit for the transmission of data that is active for the entire transmission
process
sender transmit a connection-request packet
receiver acknowledge with a connection-confirm packet
sender transmit data
sender transmit a disconnect-request packet
receiver acknowledge with a disconnect-confirm packet