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In this chapter, we introduce a wide area network (WAN), SONET, that is used as a transport network to carry loads from other WANs. We first discuss SONET as a protocol, and we then show how SONET networks can be constructed from the standards defined in the protocol. | Chapter 17 SONET/SDH Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17. SONET was developed by ANSI; SDH was developed by ITU-T. Note 17. 17-1 ARCHITECTURE Let us first introduce the architecture of a SONET system: signals, devices, and connections. Signals SONET Devices Connections Topics discussed in this section: 17. Table 17.1 SONET/SDH rates 17. Figure 17.1 A simple network using SONET equipment 17. 17-2 SONET LAYERS The SONET standard includes four functional layers: the photonic, the section, the line, and the path layer. They correspond to both the physical and the data link layers. Path Layer Line Layer Section Layer Photonic Layer Device–Layer Relationships Topics discussed in this section: 17. SONET defines four layers: path, line, section, and photonic. Note 17. Figure 17.2 SONET layers compared with OSI or the Internet layers 17. Figure 17.3 Device–layer relationship in SONET 17. 17-3 SONET FRAMES Each synchronous transfer signal STS-n is composed of 8000 frames. Each frame is a two-dimensional matrix of bytes with 9 rows by 90 × n columns. Frame, Byte, and Bit Transmission STS-1 Frame Format Encapsulation Topics discussed in this section: 17. Figure 17.4 An STS-1 and an STS-n frame 17. Figure 17.5 STS-1 frames in transmission 17. A SONET STS-n signal is transmitted at 8000 frames per second. Note 17. Each byte in a SONET frame can carry a digitized voice channel. Note 17. Find the data rate of an STS-1 signal. Solution STS-1, like other STS signals, sends 8000 frames per second. Each STS-1 frame is made of 9 by (1 × 90) bytes. Each byte is made of 8 bits. The data rate is Example 17.1 17. Find the data rate of an STS-3 signal. Solution STS-3, like other STS signals, sends 8000 frames per second. Each STS-3 frame is made of 9 by (3 × 90) bytes. Each byte is made of 8 bits. The data rate is Example 17.2 17. In SONET, the data rate of an STS-n . | Chapter 17 SONET/SDH Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17. SONET was developed by ANSI; SDH was developed by ITU-T. Note 17. 17-1 ARCHITECTURE Let us first introduce the architecture of a SONET system: signals, devices, and connections. Signals SONET Devices Connections Topics discussed in this section: 17. Table 17.1 SONET/SDH rates 17. Figure 17.1 A simple network using SONET equipment 17. 17-2 SONET LAYERS The SONET standard includes four functional layers: the photonic, the section, the line, and the path layer. They correspond to both the physical and the data link layers. Path Layer Line Layer Section Layer Photonic Layer Device–Layer Relationships Topics discussed in this section: 17. SONET defines four layers: path, line, section, and photonic. Note 17. Figure 17.2 SONET layers compared with OSI or the Internet layers 17. Figure 17.3 Device–layer relationship in SONET 17. 17-3 SONET
