1 Kyung Hee University Prof. Choong Seon HONG Switching

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)

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.

4 Kyung Hee University Switching(cont’d)  Switching method

5 Kyung Hee University 14.1 Circuit Switching ~ create a direct physical connection between two devices such as phones or computer.  Circuit-switched network

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

7 Kyung Hee University Circuit Switching(cont’d)  n-by-n folded switch can connect n lines in full-duplex mode

8 Kyung Hee University Circuit Switching(cont’d)  Circuit Switching ~ can use either two technologies.  Switching

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.

10 Kyung Hee University Circuit Switching(cont’d)  Crossbar switch

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

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

13 Kyung Hee University Circuit Switching(cont’d)  Multiple paths a. b.

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

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.

16 Kyung Hee University Circuit Switching(cont’d)  Time-division multiplexing, without and with a time-slot interchange(TSI)

17 Kyung Hee University Circuit Switching(cont’d)  Time-division multiplexing, without and with a time-slot interchange(TSI)

18 Kyung Hee University Circuit Switching(cont’d)  TSI 동작과정

19 Kyung Hee University Circuit Switching(cont’d)  TDM Bus

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)

21 Kyung Hee University Circuit Switching(cont’d)  TST switch

22 Kyung Hee University Circuit Switching(cont’d)  PSTN Hierarchy

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

24 Kyung Hee University 14.2 Packet Switching ~ data are transmitted in discrete units of potentially variable length blocks of packets.  Packet switching approaches

25 Kyung Hee University Packet Switching(cont’d)  Datagram Approach ~each packet is treated independently from all others (datagram)

26 Kyung Hee University Packet Switching(cont’d)  Multiple channels in datagram approach ~packets can be carried simultaneously by either TDM or FDM multiplexing

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)

28 Kyung Hee University Packet Switching(cont’d)  SVC(Switched Virtual Circuit) ~ is comparable conceptually to dial-up circuit switching a. b. c.

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

30 Kyung Hee University Packet Switching(cont’d)  PVC

31 Kyung Hee University Packet Switching(cont’d)  Dedicated versus shared

32 Kyung Hee University Packet Switching(cont’d)  Path versus route

33 Kyung Hee University 14.3 Message Switching  is best known by the descriptive term store and forward