Chapter 14 Other Wired Networks 14.# 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14.# 1

Chapter 14: Outline 14.1 TELEPHONE NETWORKS 14.3 SONET 14.4 ATM 14.#

14-1 TELEPHONE NETWORK The telephone network had its beginnings in the late 1800s. The entire network was originally an analog system using analog signals to transmit voice. 14.3 14.# 14.#

During the 1980s, the phone network carries data and voice. 14-1 TELEPHONE NETWORK During the 1980s, the phone network carries data and voice. The phone network is now both digital and analog. 14.4 14.# 14.#

14.14.1 Major Components The telephone network is made of three major components: local loops, trunks, and switching offices. 14.5 14.# 14.#

14.14.1 Major Components The telephone network has several levels of switching offices such as end offices, tandem offices, and regional offices. 14.6 14.# 14.#

Figure 14. 1: A telephone system 14.7 14.# 14.#

14.14.2 LATAs Local-Access Transport Areas. 14.8 14.# 14.#

14.14.2 LATAs After the divestiture of 1984 (see Appendix H), the United States was divided into more than 200 local-access transport areas (LATAs). The number of LATAs has increased since then. 14.9 14.# 14.#

Figure 14. 2: Switching offices in a LATA 14.10 14.# 14.#

Figure 14. 3: Points of presence (POPs) 14.11 14.# 14.#

Figure 14. 4: Data transfer and signaling network 14.12 14.# 14.#

Figure 14. 5: Layers in Signaling-System-7 14.13 14.# 14.#

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transport network to carry loads from other WANs. 14-3 SONET In this section, we introduce a wide area network (WAN), SONET, that is used as a transport network to carry loads from other WANs. 14.15 14.# 14.#

14.3.1 Architecture Let us first introduce the architecture of a SONET system: signals, devices, and connections.. 14.16 14.# 14.#

STS-n Synchronous Transport Signals In Europe it is called a synchronous transport module (STM) 14.#

OC-n Optical Carrier 14.#

Table 14.1: SONET rates 14.19 14.# 19

14.3.2 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 (see Figure 14.15). The headers added to the frame at the various layers are discussed later in this chapter. 14.20 14.# 14.#

14.3.2 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 (see Figure 14.15). The headers added to the frame at the various layers are discussed later in this chapter. 14.21 14.# 14.#

Figure 14.14: A simple network using SONET equipment 14.22 14.# 14.#

Figure 14.15: SONET layers compared with OSI or the Internet layers 14.23 14.# 14.#

Figure 14.16: Device-Layer relationship in SONET 14.24 14.# 14.#

Figure 14.14: A simple network using SONET equipment 14.25 14.# 14.#

14.3.3 SONET Frames Each synchronous transfer signal STS-n is composed of 8000 frames. 14.26 14.# 14.#

14.3.3 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. 14.27 14.# 14.#

14.3.3 SONET Frames For example, an STS-1 frame is 9 rows by 90 columns (810 bytes), and an STS-3 is 9 rows by 270 columns (2430 bytes). Figure 14.17 shows the general format of an STS-1 and an STS-n. 14.28 14.# 14.#

Figure 14.17: An STS-1 and an STS-n frame 14.29 14.# 14.#

Figure 14.18: STS-1 frames in transition 14.30 14.# 14.#

14.3.1 Architecture Let us first introduce the architecture of a SONET system: signals, devices, and connections.. 14.31 14.# 14.#

Example 14.1 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 14.32 14.# 32

Example 14.2 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 14.33 14.# 33

Example 14.3 What is the duration of an STS-1 frame? STS-3 frame? STS-n frame? Solution In SONET, 8000 frames are sent per second. This means that the duration of an STS-1, STS-3, or STS-n frame is the same and equal to 1/8000 s, or 125 μs. 14.34 14.# 34

SPE Synchronous Payload Envelope 14.#

Figure 14.19: STS-1 frame overheads 14.36 14.# 14.#

Figure 14.14: A simple network using SONET equipment 14.37 14.# 14.#

Figure 14.20: STS-1 frame: section overheads 14.38 14.# 14.#

Figure 14.21: STS-1 frame: line overhead 14.39 14.# 14.#

Figure 14.22: STS-1 frame path overhead 14.40 14.# 14.#

Table 14.2: SONETs overhead 14.41 14.# 41

Example 14.4 What is the user data rate of an STS-1 frame (without considering the overheads)? Solution The user data part of an STS-1 frame is made of 9 rows and 86 columns. So we have 14.42 14.# 42

Figure 14.23: Offsetting of SPE related to frame boundary 14.43 14.# 14.#

Figure 14.24: The use of H1 and H2 to show the start of SPE 14.44 14.# 14.#

14.3.4 STS Multiplexing In SONET, frames of lower rate can be synchronously time-division multiplexed into a higher-rate frame. 14.45 14.# 14.#

14.3.4 STS Multiplexing For example, three STS-1 signals (channels) can be combined into one STS-3 signal (channel), four STS-3s can be multiplexed into one STS-12, and so on. 14.46 14.# 14.#

Figure 14.25: STS multiplexing/demultiplexing 14.47 14.# 14.#

Figure 14.26: Byte interleaving (bytes remain in the same row) 14.48 14.# 14.#

Figure 14.27: An STS-3 frame 14.49 14.# 14.#

Figure 14.28: A concatenated STS-3c signal 14.50 14.# 14.#

Figure 14.29: Dropping and adding frames in an add/drop multiplexer 14.51 14.# 14.#

14.3.5 SONET Networks Using SONET equipment, we can create a SONET network that can be used as a high-speed backbone carrying loads from other networks such as ATM (Section 14.4) or IP (Chapter 19). 14.52 14.# 14.#

14.3.5 SONET Networks SONET networks are divided into three categories: linear, ring, and mesh networks 14.53 14.# 14.#

Figure 14.30: Taxonomy of SONET networks 14.54 14.# 14.#

Figure 14.34: A unidirectional path switching ring 14.55 14.# 14.#

Figure 14.35: A bidirectional switching ring 14.56 14.# 14.#

Figure 14. 36: A combination of rings 14.57 14.# 14.#

Figure 14.37: A mesh SONET network 14.58 14.# 14.#

14.3.6 Virtual Tributaries SONET is designed to carry broadband payloads. To make SONET backward-compatible with the current hierarchy, its frame design includes a system of virtual tributaries (VTs) (see Figure 14.38). 14.59 14.# 14.#

14.3.6 Virtual Tributaries A virtual tributary is a partial payload that can be inserted into an STS-1 and combined with other partial payloads to fill out the frame. Instead of using all 86 payload columns of an STS-1 frame for data from one source, we can subdivide the SPE and call each component a VT. 14.60 14.# 14.#

Figure 14.38: Virtual tributaries 14.61 14.# 14.#

Figure 14.39: Virtual tributary types 14.62 14.# 14.#

Asynchronous Transfer Mode (ATM) The combination of ATM and SONET will allow high-speed interconnection of all the world’s networks. 14.63 14.# 14.#

14.4.2 Problems Before we discuss the solutions to these design requirements, it is useful to examine some of the problems associated with existing systems. 14.64 14.# 14.#

Figure 14.40: Multiplexing using different frame size 14.65 14.# 14.#

Figure 14.41: Multiplexing using cells 14.66 14.# 14.#

Figure 14.42: ATM multiplexing 14.67 14.# 14.#

14.4.3 Architecture ATM is a cell-switched network. The user access devices, called the endpoints, are connected through a user-to-network interface (UNI) to the switches inside the network. The switches are connected through network-to-network interfaces (NNIs). Figure 14.43 shows an example of an ATM network. 14.68 14.# 14.#

Figure 14.43: Architecture of an ATM network 14.69 14.# 14.#

Figure 14.45: Virtual connection identifiers in UNIs and NNIs 14.70 14.# 14.#

Figure 14.46: An ATM cell 14.71 14.# 14.#

Figure 14.47: Routing with a switch 14.72 14.# 14.#

Figure 14.49: AAL5 14.73 14.# 14.#