1. 13장 SWITCHING : A NETWORK LAYER FUNCTION
13.1 회선교환(Circuit Switching)
13.2 패킷 교환(Packet Switching)
13.3 메시지 교환(Message Switching)
13.4 네트워크층
13.5 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. 13.1 Circuit Switching
~ create a direct physical connection between two devices such as phones or computer.
Circuit-switched network

5. Circuit Switching(cont’d)
~ 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)
~ 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 a. b.

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. 13.2 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. 13.3 Message Switching
~ is best known by the descriptive term store and forward

27. 13.4 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. 13.5 요약