Chapter 8 Switching Http netwk hannam ac kr

Chapter 8 교환 (Switching) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 1

교환 네트워크 종류 ■ 회선 교환(circuit switching) ■ 패킷 교환(packet switching) ■ 메시지 교환(message switching) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 4

8 -1 CIRCUIT-SWITCHED NETWORKS A circuit-switched network consists of a set of switches connected by physical links. A connection between two stations is a dedicated path made of one or more links. However, each connection uses only one dedicated channel on each link. Each link is normally divided into n channels by using FDM or TDM. Topics discussed in this section: Three Phases Efficiency Delay Circuit-Switched Technology in Telephone Networks Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 5

8. 1 회선 교환 네트워크 q 간단한 회선 교환 네트워크 Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 6

회선 교환 네트워크는 각 링크를 n개의 채널로 나누는 물리적인 링크에 의해 연결된 교 환기의 집합으로 이루어진다 A circuit-switched network is made of a set of switches connected by physical links, in which each link is divided into n channels. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 7

회선 교환에서는 설정 단계에서 자원 할당이 필요하며, 해제 단계에 들기 전까지는 계속해서 전체 데이터 전송 기간 동안 전용적으로 할당되어야 한다 In circuit switching, the resources need to be reserved during the setup phase; the resources remain dedicated for the entire duration of data transfer until the teardown phase. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 8

Example 8. 1 As a trivial example, let us use a circuit-switched network to connect eight telephones in a small area. Communication is through 4 -k. Hz voice channels. We assume that each link uses FDM to connect a maximum of two voice channels. The bandwidth of each link is then 8 k. Hz. Figure 8. 4 shows the situation. Telephone 1 is connected to telephone 7; 2 to 5; 3 to 8; and 4 to 6. Of course the situation may change when new connections are made. The switch controls the connections. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 9

Example 8. 2 As another example, consider a circuit-switched network that connects computers in two remote offices of a private company. The offices are connected using a T-1 line leased from a communication service provider. There are two 4 × 8 (4 inputs and 8 outputs) switches in this network. For each switch, four output ports are folded into the input ports to allow communication between computers in the same office. Four other output ports allow communication between the two offices. Figure 8. 5 shows the situation. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 11

회선 교환 네트워크 q Delay in a circuit-switched network Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 14

전통적인 전화 네트워크에서 물리층 교환은 회선 교환 방식을 사용한다. Switching at the physical layer in the traditional telephone network uses the circuit-switching approach. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 15

8 -2 DATAGRAM NETWORKS In data communications, we need to send messages from one end system to another. If the message is going to pass through a packet-switched network, it needs to be divided into packets of fixed or variable size. The size of the packet is determined by the network and the governing protocol. Topics discussed in this section: Routing Table Efficiency Delay Datagram Networks in the Internet Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 16

패킷 교환망에서 자원 예약은 없으며, 자원은 필요에 따라 할당된다. In a packet-switched network, there is no resource reservation; resources are allocated on demand. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 17

데이터그램 네트워크 q 데이터그램망에서의 경로표(Routing table) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 19

데이터그램 망의 교환기는 목적지 주소를 기 반으로 한 경로 표를 가지고 있다. A switch in a datagram network uses a routing table that is based on the destination address. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 20

데이터그램 망에서 헤더의 목적지 주소는 패 킷이 전송되는 동안 내내 같은 값을 유지한다 The destination address in the header of a packet in a datagram network remains the same during the entire journey of the packet Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 21

인터넷에서 교환은 네트워크 층에서 패킷을 교환하는 데이터그램 방식이다 Switching in the Internet is done by using the datagram approach to packet switching at the network layer Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 23

8 -3 VIRTUAL-CIRCUIT NETWORKS A virtual-circuit network is a cross between a circuitswitched network and a datagram network. It has some characteristics of both. Topics discussed in this section: Addressing Three Phases Efficiency Delay Circuit-Switched Technology in WANs Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 24

가상회선 네트워크 Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 26

가상회선 네트워크 q 가상회선 식별자 Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 28

가상회선 교환에서 같은 발신지와 목적지에 속한 모든 패킷은 동일한 경로를 거치지만 한정된 자원에 대해 서로 다른 지연으로 목적지에 도착할 수 있다 In virtual-circuit switching, all packets belonging to the same source and destination travel the same path; but the packets may arrive at the destination with different delays if resource allocation is on demand. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 33

가상회선 네트워크 q 가상회선 네트워크에서의 지연 Total delay = 3 T + 3π + setup delay + teardown delay Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 34

교환식 WAN에서 링크 계층 교환은 보통 가상회선 기술들을 사용하여 구현된다 Switching at the data link layer in a switched WAN is normally implemented by using virtual-circuit techniques. Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 35

8 -4 STRUCTURE OF A SWITCH We use switches in circuit-switched and packetswitched networks. In this section, we discuss the structures of the switches used in each type of network. Topics discussed in this section: Structure of Circuit Switches(회선 교환) Structure of Packet Switches(패킷 교환) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 36

스위치 구조 q 회선 교환 Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 37

스위치 구조 q Crossbar 교환 ■ 3개의 입력과 4개의 출력을 갖는 크로스바 교환기(Crossbar switch) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 39

In a three-stage switch, the total number of crosspoints is 2 k. N + k(N/n)2 which is much smaller than the number of crosspoints in a single-stage switch (N 2) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 41

Example 8. 3 Design a three-stage, 200 × 200 switch (N = 200) with k = 4 and n = 20 Solution In the first stage we have N/n or 10 crossbars, each of size 20 × 4. In the second stage, we have 4 crossbars, each of size 10 × 10. In the third stage, we have 10 crossbars, each of size 4 × 20. The total number of crosspoints is 2 k. N + k(N/n)2, or 2000 crosspoints. This is 5 percent of the number of crosspoints in a single-stage switch (200 × 200 = 40, 000) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 42

According to the Clos criterion: n = (N/2)1/2 k > 2 n – 1 Crosspoints ≥ 4 N [(2 N)1/2 – 1] Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 43

Example 8. 4 Redesign the previous three-stage, 200 × 200 switch, using the Clos criteria with a minimum number of crosspoints. Solution We let n = (200/2)1/2, or n = 10. We calculate k = 2 n − 1 = 19. In the first stage, we have 200/10, or 20, crossbars, each with 10 × 19 crosspoints. In the second stage, we have 19 crossbars, each with 10 × 10 crosspoints. In the third stage, we have 20 crossbars each with 19 × 10 crosspoints. The total number of crosspoints is 20(10 × 19) + 19(10 × 10) + 20(19 × 10) = 9500 Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 44

스위치 구조 q 시 분할(Time Division) 교환 ■ TDM(Time-division multiplexing)과 TSI(Time-Slot Interchange) 을 이용해 확립 ■ TSI : 요구되는 연결상에 기반으로 한 슬롯의 번호를 변경 Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 45

스위치 구조 q TSI (Time-Slot Interchange) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 47

스위치 구조 q 반얀 교환기(Banyan switch) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 52

스위치 구조 q 반얀 교환기(Banyan switch)의 경로 지정 예 Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 53

스위치 구조 q 뱃처 반얀 교환기(Batcher-Banyan switch) Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 54

8. 3 요약 Http: //netwk. hannam. ac. kr HANNAM UNIVERSITY 55