Chapter 14

OtherWired

Networks

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Chapter 14: Outline

14.1 14.1 TELEPHONE NETWORKSTELEPHONE NETWORKS

14.3 14.3 SONETSONET

14.4 14.4 ATMATM

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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.

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14-1 TELEPHONE NETWORK14-1 TELEPHONE NETWORK

During the 1980s, the phone network carries data and voice.

The phone network is now both digital and analog.

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14.14.1 Major Components14.14.1 Major Components

The telephone network is made of three major components: local loops, trunks, and switching offices.

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14.14.1 Major Components14.14.1 Major Components

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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14.14.2 LATAs14.14.2 LATAs

Local-Access Transport Areas.

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14.14.2 LATAs14.14.2 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.

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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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Figure 14. 4: Data transfer and signaling network

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

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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.

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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..

STS-n

Synchronous Transport Signals In Europe it is called a synchronous

transport module (STM)

OC-n

Optical Carrier

Table 14.1: SONET rates

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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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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 14.14: A simple network using SONET equipment

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

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Figure 14.16: Device-Layer relationship in SONET

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Figure 14.14: A simple network using SONET equipment

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14.3.3 SONET Frames14.3.3 SONET Frames

Each synchronous transfer signal STS-n is composed of 8000 frames.

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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.

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14.3.3 SONET Frames14.3.3 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.

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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

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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..

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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SPE

Synchronous Payload Envelope

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Figure 14.19: STS-1 frame overheads

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Figure 14.14: A simple network using SONET equipment

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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

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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.

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14.3.4 STS Multiplexing14.3.4 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.

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Figure 14.25: STS multiplexing/demultiplexing

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Figure 14.26: Byte interleaving (bytes remain in the same row)

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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).

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14.3.5 SONET Networks14.3.5 SONET Networks

SONET networks are divided into three categories:

linear, ring, and mesh networks

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Figure 14.30: Taxonomy of SONET 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. To make SONET backward-compatible with the current hierarchy, its frame design includes a system of virtual tributaries (VTs) (see Figure 14.38).

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14.3.6 Virtual Tributaries14.3.6 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.

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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)

The combination of ATM and SONET will allow high-speed interconnection of all the world’s networks.

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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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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 14.45: 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 14.49: AAL5