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Published byGriselda Wilson Modified over 9 years ago
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1 Kyung Hee University Prof. Choong Seon HONG Switching
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2 Kyung Hee University 14 장 SWITCHING : 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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3 Kyung Hee University 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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4 Kyung Hee University Switching(cont’d) Switching method
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5 Kyung Hee University 14.1 Circuit Switching ~ create a direct physical connection between two devices such as phones or computer. Circuit-switched network
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6 Kyung Hee University 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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7 Kyung Hee University Circuit Switching(cont’d) n-by-n folded switch can connect n lines in full-duplex mode
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8 Kyung Hee University Circuit Switching(cont’d) Circuit Switching ~ can use either two technologies. Switching
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9 Kyung Hee University 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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10 Kyung Hee University Circuit Switching(cont’d) Crossbar switch
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11 Kyung Hee University Circuit Switching(cont’d) Limitation of crossbar switch The number of switch(huge size) : connect n inputs by m output l require n * m crosspoint. (ex : 1000 input, 1000 output → 1,000,000 crosspoint) inefficient l fewer than 25% of the crosspoints are in use at a given time. l the rest are idle
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12 Kyung Hee University 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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13 Kyung Hee University Circuit Switching(cont’d) Multiple paths a. b.
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14 Kyung Hee University 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 l need 225 crosspoint(15 * 15) multistage switch l first-stage : 10 crosspoint(5 * 2) *3 = 30 crosspoint l second-stage : 9 crosspoint(3 *3) * 2 = 18 crosspoint l third-stage : 10 crosspoint(5 * 2) *3 = 30 crosspoint total number of crosspoint : 78
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15 Kyung Hee University 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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16 Kyung Hee University Circuit Switching(cont’d) Time-division multiplexing, without and with a time-slot interchange(TSI)
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17 Kyung Hee University Circuit Switching(cont’d) Time-division multiplexing, without and with a time-slot interchange(TSI)
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18 Kyung Hee University Circuit Switching(cont’d) TSI 동작과정
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19 Kyung Hee University Circuit Switching(cont’d) TDM Bus
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20 Kyung Hee University 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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21 Kyung Hee University Circuit Switching(cont’d) TST switch
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22 Kyung Hee University Circuit Switching(cont’d) PSTN Hierarchy
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23 Kyung Hee University 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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24 Kyung Hee University 14.2 Packet Switching ~ data are transmitted in discrete units of potentially variable length blocks of packets. Packet switching approaches
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25 Kyung Hee University Packet Switching(cont’d) Datagram Approach ~each packet is treated independently from all others (datagram)
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26 Kyung Hee University Packet Switching(cont’d) Multiple channels in datagram approach ~packets can be carried simultaneously by either TDM or FDM multiplexing
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27 Kyung Hee University 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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28 Kyung Hee University Packet Switching(cont’d) SVC(Switched Virtual Circuit) ~ is comparable conceptually to dial-up circuit switching a. b. c.
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29 Kyung Hee University 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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30 Kyung Hee University Packet Switching(cont’d) PVC
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31 Kyung Hee University Packet Switching(cont’d) Dedicated versus shared
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32 Kyung Hee University Packet Switching(cont’d) Path versus route
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33 Kyung Hee University 14.3 Message Switching is best known by the descriptive term store and forward
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