1. 1 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

2. 2 Switching(cont’d) zSwitching ~whenever we have multiple devices, we have the problem the problem of how to connect them to make one-one-one communication possible.

3. 3 Switching(cont’d) zSwitching method

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

5. 5 Circuit Switching(cont’d) zCircuit Switching ~is a device with n inputs and m outputs that creates a temporary connection between an input link and output link. zA circuit switch

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

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

8. 8 Circuit Switching(cont’d) zSpace-Division Switches ythe paths in the circuit are separated from each other spatially(crossbar switch) zCrossbar switch ~ connect n input to m output in a grid, using electronic microswitch(transistor) at each crosspoint.

9. 9 Circuit Switching(cont’d) zCrossbar switch

10. 10 Circuit Switching(cont’d) zLimitation of crossbar switch yThe number of switch(huge size) : connect n inputs by m output -- require n * m crosspoint. (ex : 1000 input, 1000 output → 1,000,000 crosspoint) yinefficient ~ fewer than 25% of the crosspoint are in use at a given time.

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

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

13. 13 Circuit Switching(cont’d) zBlock ~compare the number of crosspoints in a 15-by-15 single-stage crossbar switch with the 15-by-15 multistage switch. ysingle-stage switch ~ need 225 crosspoint(15 * 15) ymultistage 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. 14 Circuit Switching(cont’d) zTime-Division Switch ~is accomplished using TDM(Time-division multiplexing) and TSI(Time-Slot Interchange) yTSI - change the ordering of the slots based on the desired connections.

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

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

17. 17 Circuit Switching(cont’d) zTSI 동작과정

18. 18 Circuit Switching(cont’d) zSpace-and Time-Division Switching Combinations ~ combine space-division and time-division technology to take advantage of the best of both yTST(time-space-time) yTSST(time-space-space-time) ySTTS(space-time-time-space)

19. 19 Circuit Switching(cont’d) zTST switch

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

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

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

23. 23 Packet Switching(cont’d) zVirtual Circuit Approach ~A single route is chosen between sender and receiver at the beginning of the session ySVC(Switched Virtual Circuit) yPVC(Permanent Virtual Circuit)

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

25. 25 Packet Switching(cont’d) zPVC(Permanent Virtual Circuit) ~ is comparable to leased lines ysame virtual circuit is provided between two users on a continuous basis ycircuit is dedicated to the specific user ytwo PVC user always get the same route

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

27. 27 14.4 Network Layer ~is responsible for establishing, managing, and termination connections between physical network yprotocols at this layer provide transparent routing and relaying services between networks yOSI model support two type of protocol : CONS and CLNS

28. 28 Network Layer(cont’d) zCONS(Connection-Oriented Network Service) ~establishes a virtual circuit for the transmission of data that is active for the entire transmission yprocess  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. 29 Network Layer(cont’d) zCLNS(Connection less Network Service) ~each packet of a multipacket transmission is treated as an independent unit yprocess ~ is simpler than that of a CONS  Sender transmit data