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14 장 SWITCHING : A NETWORK LAYER FUNCTION

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. Switching(cont’d). Switching

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14 장 SWITCHING : A NETWORK LAYER FUNCTION

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  1. 14장 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

  2. 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.

  3. Switching(cont’d) • Switching method

  4. 14.1 Circuit Switching ~ create a direct physical connection between two devices such as phones or computer. • Circuit-switched network

  5. 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

  6. Circuit Switching(cont’d) • n-by-n folded switch can connect n lines in full-duplex mode

  7. Circuit Switching(cont’d) • Circuit Switching ~ can use either two technologies. • Switching

  8. 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.

  9. Circuit Switching(cont’d) • Crossbar switch

  10. 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.

  11. Circuit Switching(cont’d) • Multistage Switches ~ devices are linked to switches that, in turn are linked to a hierarchy of other switches

  12. Circuit Switching(cont’d) • Multiple paths b. a.

  13. 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

  14. 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.

  15. Circuit Switching(cont’d) • Time-division multiplexing, without and with a time-slot interchange(TSI) - No switching

  16. Circuit Switching(cont’d) • Time-division multiplexing, without and with a time-slot interchange(TSI) - Switching

  17. Circuit Switching(cont’d) • TSI 동작과정

  18. 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)

  19. Circuit Switching(cont’d) • TST switch

  20. 14.2 Packet Switching ~ data are transmitted in discrete units of potentially variable length blocks cabled packets. • Packet switching approaches

  21. Packet Switching(cont’d) • Datagram Approach ~ each packet is treated independently from all others (datagram)

  22. Packet Switching(cont’d) • Multiple channels in datagram approach ~ packets can be carried simultaneously by either TDM or FDM multiplexing

  23. 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)

  24. Packet Switching(cont’d) • SVC(Switched Virtual Circuit) ~ is comparable conceptually to dial-up circuit switching a. b. c.

  25. 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

  26. 14.3 Message Switching ~ is best known by the descriptive term store and forward

  27. 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

  28. 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

  29. Network Layer(cont’d) • CLNS(Connection less Network Service) ~ each packet of a multipacket transmission is treated as an independent unit • process ~ is simpler than that of a CONS  Sender transmit data

  30. 14.5 요약

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