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

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.

Switching(cont’d) Switching method

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

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

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

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

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.

Circuit Switching(cont’d) Crossbar switch

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.

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

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

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

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.

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

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

Circuit Switching(cont’d) TSI 동작과정

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)

Circuit Switching(cont’d) TST switch

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

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

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

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)

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

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

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

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

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

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

13.5 요약