Chapter 14

OtherWired

Networks

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Chapter 14: Outline

14.1 14.1 TELEPHONE NETWORKSTELEPHONE NETWORKS

14.2 14.2 CABLE NETWORKSCABLE NETWORKS

14.3 14.3 SONETSONET

14.4 14.4 ATMATM

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Chapter 14: Objective

The first section discusses the telephone network. It describes the telephone network as a voice network. It then shows how the voice network has been used for data transmission either as a dial-up service or DSL service.

The second section discusses the cable network. It first briefly describes it as a video network. The section then shows how the video network has been used for data transmission.

The third section discusses SONET, both as a fiber-optic technology and a network. The section shows how the technology can be used for high-speed connection to carry data.

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Chapter 14: Objective (continued)

The fourth section discusses ATM, which can use SONET as the

carrier to create a high-speed wide area network (WAN). ATM is a cell-relay network that uses a fixed-size frame (cell) as the unit of transmitted data.

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14-1 TELEPHONE NETWORK14-1 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. With the advent of the computer era, the network, in the 1980s, began to carry data in addition to voice. During the last decade, the telephone network has undergone many technical changes. The network is now digital as well as analog.

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14.1.1 Major Components14.1.1 Major Components

The telephone network, as shown in Figure 14.1, is made of three major components: local loops, trunks, and switching offices. The telephone network has several levels of switching offices such as end offices, tandem offices, and regional offices.

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Figure 14.1: A telephone system

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14.1.2 LATAs14.1.2 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. A LATA can be a small or large metropolitan area. A small state may have a single LATA; a large state may have several LATAs. A LATA boundary may overlap the boundary of a state; part of a LATA can be in one state, part in another state.

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Figure 14.2: Switching offices in a LATA

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Figure 14.3: Points of presence (POPs)

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14.1.3 Signaling14.1.3 Signaling

The telephone network, at its beginning, used a circuit-switched network with dedicated links to transfer voice communication. The operator connected the two parties by using a wire with two plugs inserted into the corresponding two jacks. Later, the signaling system became automatic. Rotary telephones were invented that sent a digital signal defining each digit in a multi-digit telephone number. As telephone networks evolved into a complex network, the functionality of the signaling system increased. The signaling system was required to perform other tasks.

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Figure 14.4: Data transfer and signaling network

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Figure 14.5: Layers in SS7

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14.1.4 Services14.1.4 Services

Telephone companies provide two types of services: analog and digital.

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14.1.5 Dial-Up Service14.1.5 Dial-Up Service

Traditional telephone lines can carry frequencies between 300 and 3300 Hz, giving them a bandwidth of 3000 Hz.

A dial-up service uses a modem to send data through telephone lines.

The term modem is a composite word that refers to the two functional entities that make up the device: a signal modulator and a signal demodulator.

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Figure 14.6: Telephone line bandwidth

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Figure 14.7: Modulation/demodulation

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Figure 14.8: Dial-up network to provide Internet access

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14.1.6 Digital Subscriber Line (DSL)14.1.6 Digital Subscriber Line (DSL)

After traditional modems reached their peak data rate, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet. Digital subscriber line (DSL) technology is one of the most promising for supporting high-speed digital communication over the existing telephone. DSL technology is a set of technologies, each differing in the first letter (ADSL, VDSL, HDSL, and SDSL).

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Figure 14.9: ASDL point-to-point network

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14-2 CABLE NETWORK14-2 CABLE NETWORK

The cable networks became popular with people who just wanted a better signal. In addition, cable networks enabled access to remote broadcasting stations via microwave connections. Cable TV also found a good market in Internet access provision, using some ofthe channels originally designed for video.

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14.2.1 Traditional Cable Networks14.2.1 Traditional Cable Networks

Cable TV started to distribute broadcast video signals to locations with poor or no reception in the late 1940s. It was called community antenna television (CATV) because an antenna at the top of a tall hill or building received the signals from the TVstations and distributed them, via coaxial cables, to the community. Figure 14.10 shows a schematic diagram of a traditional cable TV network.

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Figure 14.10: Traditional cable TV network

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14.2.2 HFC Network14.2.2 HFC Network

The second generation of cable network is called a hybrid fiber-coaxial (HFC) network. The network uses a combination of fiber-optic and coaxial cable. The transmission medium from the cable TV office to a box, called the fiber node, is optical fiber; from the fiber node through the neighborhood and into the house is still coaxial cable. Figure 14.11 shows a schematic diagram of an HFC network.

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Figure 14.11: Hybrid Fiber-Coaxial (HFC) Network

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14.2.3 14.2.3 Cable TV for Data TransferCable TV for Data Transfer

Cable companies are now competing with telephone companies for the residential customer who wants high-speed data transfer. DSL technology provides high-data-rate connections for residential subscribers over the local loop. However, DSL uses the existing unshielded twisted-pair cable, which is very susceptible to interference. This imposes an upper limit on the data rate. A solution is the use of the cable TV network. In this section, we briefly discuss this technology.

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Figure 14.12: Division of coaxial cable band by CATV

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Figure 14.13: Cable modem transmission system (CMTS)

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14-3 SONET14-3 SONET

In this section, we introduce a wide area network (WAN), SONET, that is used as atransport 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.

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14.3.1 Architecture14.3.1 Architecture

Let us first introduce the architecture of a SONET system: signals, devices, and connections..

Table 14.1: SONET rates

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Figure 14.14: A simple network using SONET equipment

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14.3.2 SONET Layers14.3.2 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.

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Figure 14.15: SONET layers compared with OSI or the Internet layers

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14.3.3 SONET Frames14.3.3 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. 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.

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Figure 14.16: Device-Layer relationship in SONET

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Figure 14.17: An STS-1 and an STS-n frame

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Figure 14.18: STS-1 frames in transition

Find the data rate of an STS-1 signal.

SolutionSTS-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 14.1

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Find the data rate of an STS-3 signal.

SolutionSTS-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 14.2

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What is the duration of an STS-1 frame? STS-3 frame? STS-n frame?

SolutionIn 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.

Example 14.3

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Figure 14.19: STS-1 frame overheads

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Figure 14.20: STS-1 frame: section overheads

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Figure 14.21: STS-1 frame: line overhead

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Figure 14.22: STS-1 frame path overhead

Table 14.2: SONETs overhead

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What is the user data rate of an STS-1 frame (without considering the overheads)?

SolutionThe user data part of an STS-1 frame is made of 9 rows and 86 columns. So we have

Example 14.4

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Figure 14.23: Offsetting of SPE related to frame boundary

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Figure 14.24: The use of H1 and H2 to show the start of SPE

What are the values of H1 and H2 if an SPE starts at byte number 650?

SolutionThe number 650 can be expressed in four hexadecimal digits as 0x028A. This means the value of H1 is 0x02 and the value of H2 is 0x8A.

Example 14.5

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14.3.4 STS Multiplexing14.3.4 STS Multiplexing

In SONET, frames of lower rate can be synchronously time-division multiplexed into a higher-rate frame. 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, as shown in Figure 14.25.

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Figure 14.25: STS multiplexing/demultiplexing

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Figure 14.26: Byte interleaving

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Figure 14.27: An STS-3 frame

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Figure 14.28: A concatenated STS-3c signal

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Figure 14.29: Dropping and adding frames in an add/drop multiplexer

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14.3.5 SONET Networks14.3.5 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). We can roughly divide SONET networks into three categories: linear, ring, and mesh networks, as shown in Figure 14.30..

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Figure 14.30: Taxonomy of SONET networks

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Figure 14.31: A point-to-point SONET network

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Figure 14.32: A linear SONET network

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Figure 14.33: Automatic protection switching in linear networks

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Figure 14.34: A unidirectional path switching ring

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Figure 14.35: A bidirectional switching ring

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Figure 14.36: A combination of rings

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Figure 14.37: A mesh SONET network

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14.3.6 Virtual Tributaries14.3.6 Virtual Tributaries

SONET is designed to carry broadband payloads. Current digital hierarchy data rates (DS-1 to DS-3), however, are lower than STS-14.To make SONET backward-compatible with the current hierarchy, its frame design includes a system of virtual tributaries (VTs) (see Figure 14.38). 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.

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Figure 14.38: Virtual tributaries

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Figure 14.39: Virtual tributary types

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14-4 ATM14-4 ATM

Asynchronous Transfer Mode (ATM) is a switched wide area network based on the cell relay protocol designed by the ATM forum and adopted by the ITU-T. The combination of ATM and SONET will allow high-speed interconnection of all the world’s networks. In fact, ATM can be thought of as the “highway” of the information superhighway.

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14.4.1 Design Goals14.4.1 Design Goals

Among the challenges faced by the designers of ATM, six stand out.1.The need for a transmission system to optimize the use of high-data-rate.2.The system must interface with existing systems. 3.The design must be implemented inexpensively.4.The new system must be able to work with and support the existing hierarchies 5.The new system must be connection-oriented. 6.Last but not least, one objective is to move as many of the functions to hardware as possible.

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14.4.2 Problems14.4.2 Problems

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

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Figure 14.40: Multiplexing using different frame size

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A cell network uses the cell as the basic unit of data exchange.

A cell is defined as a small, fixed-size block of information.

Note

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Figure 14.41: Multiplexing using cells

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Figure 14.42: ATM multiplexing

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14.4.3 Architecture14.4.3 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.

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Figure 14.43: Architecture of an ATM network

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Figure 14.44: TP, VPs, and VCs

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Figure 18.11 Example of VPs and VCs

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Note that a virtual connection is defined by a pair of numbers:

the VPI and the VCI.

Note

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Figure 18.12 Connection identifiers

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Figure 14.45: Virtual connection identifiers in UNIs and NNIs

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Figure 18.13 Virtual connection identifiers in UNIs and NNIs

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Figure 14.46: An ATM cell

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Figure 14.47: Routing with a switch

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Figure 14.48: ATM layers

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Figure 18.18 ATM layer

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Figure 18.19 ATM headers

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Figure 18.20 AAL1

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Figure 18.21 AAL2

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Figure 18.22 AAL3/4

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Figure 18.23 AAL5

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Figure 14.49: AAL5

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18-3 ATM LANs18-3 ATM LANs

ATM is mainly a wide-area network (WAN ATM); ATM is mainly a wide-area network (WAN ATM); however, the technology can be adapted to local-area however, the technology can be adapted to local-area networks (ATM LANs). The high data rate of the networks (ATM LANs). The high data rate of the technology has attracted the attention of designers technology has attracted the attention of designers who are looking for greater and greater speeds in who are looking for greater and greater speeds in LANs. LANs.

ATM LAN ArchitectureLAN Emulation (LANE)Client/Server ModelMixed Architecture with Client/Server

Topics discussed in this section:Topics discussed in this section:

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Figure 18.24 ATM LANs

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Figure 18.25 Pure ATM LAN

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Figure 18.26 Legacy ATM LAN

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Figure 18.27 Mixed architecture ATM LAN

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Figure 18.28 Client and servers in a LANE

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Figure 18.29 Client and servers in a LANE