Đang chuẩn bị liên kết để tải về tài liệu:
Lecture Data communications and networks: Chapter 8 - Forouzan 

We have seen in Chapter 3 that a digital signal is superior to an analog signal. The tendency today is to change an analog signal to digital data. In this section we describe two techniques, pulse code modulation and delta modulation. | Chapter 8 Switching Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8. Figure 8.1 Switched network 8. Figure 8.2 Taxonomy of switched networks 8. 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. Three Phases Efficiency Delay Circuit-Switched Technology in Telephone Networks Topics discussed in this section: 8. A circuit-switched network is made of a set of switches connected by physical links, in which each link is divided into n channels. Note 8. Figure 8.3 A trivial circuit-switched network 8. 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. Note 8. As a trivial example, let us use a circuit-switched network to connect eight telephones in a small area. Communication is through 4-kHz 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 kHz. 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. Example 8.1 8. Figure 8.4 Circuit-switched network used in Example 8.1 8. 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 . | Chapter 8 Switching Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 8. Figure 8.1 Switched network 8. Figure 8.2 Taxonomy of switched networks 8. 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. Three Phases Efficiency Delay Circuit-Switched Technology in Telephone Networks Topics discussed in this section: 8. A circuit-switched network is made of a set of switches connected by physical links, in which each link is divided into n channels. Note 8. Figure 8.3 A trivial circuit-switched network 8. In circuit switching, the resources need to be reserved during the setup phase; the resources remain dedicated for the entire duration of .