Chapter 14 Other Wired Networks
Transcript of Chapter 14 Other Wired Networks
Chapter 14
Other
Wired
Networks
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Chapter 14: Outline
14.1 TELEPHONE NETWORKS
14.2 CABLE NETWORKS
14.3 SONET
14.4 ATM
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.
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.
14.5
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. 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.
14.6
14.1.1 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.
Figure 14.1
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14.1.2 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 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 Services
Telephone companies provide two types of
services: analog and digital.
• Analog services
• Analog switched service: dial-up, 800
service, 900 service
• Analog leased service: dedicated line
• Digital services
• Switched/56 service: switched, 56 kbps
• Digital data service: leased, 64 kbps
14.14
14.1.5 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
Audio frequency shift keying:
originating modem sends 0s by playing a 1,070 Hz tone, and 1s at 1,270 Hz;
answering modem transmitting its 0s on 2,025 Hz and 1s on 2,225 Hz.
Phase-shift keying:
two tones for any one side of the connection are sent at similar frequencies,
but slightly out of phase.
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Figure 14. 7: Modulation/demodulation
14.17
Figure 14.8: Dial-up network to provide Internet access
14.18
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).
14.19
Figure 14.9: ADSL point-to-point network
14.20
14-2 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 of the channels originally designed
for video.
14.21
14.2.1 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 TV stations 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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14.24
14.2.2 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.
14.25
Figure 14.11: Hybrid Fiber-Coaxial (HFC) Network
14.26
14.27
14.2.3 Cable 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.
14.28
Figure 14.12: Division of coaxial cable band by CATV
14.29
Figure 14.13: Cable modem transmission system (CMTS)
14.30
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. 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 Architecture
Let us first introduce the architecture of a
SONET system: signals, devices, and
connections.
Table 14.1: SONET rates
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Signals
ITU-T SDHANSI SONET
14.33
Figure 14.14: A simple network using SONET equipment
Devices
Connections
14.34
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.
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Figure 14.15: SONET layers compared with OSI or the Internet layers
14.36
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. 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.
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 14.1
14.40
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 14.2
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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.
Example 14.3
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14.43
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
14.47
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
Example 14.4
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14.49
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?
Solution
The 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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14.52
14.3.4 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
14.57
Figure 14.29: Dropping and adding frames in an add/drop multiplexer
14.58
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). We can roughly divide SONET
networks into three categories: linear, ring, and
mesh networks, as shown in Figure 14.30.
14.59
Figure 14.30: Taxonomy of SONET networks
14.60
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 Tributaries
SONET is designed to carry broadband
payloads. Current digital hierarchy data rates
(DS-1 to DS-3), however, are lower than STS-1.
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
14.70
14-4 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 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 Problems
Before we discuss the solutions to these design
requirements, it is useful to examine some of the
problems associated with existing systems.
• Different protocols use frames of varying size
• As networks become more complex,
information that must be carried in the header
becomes more extensive
• Larger header
• Enlarge date unit size: often a waste
• Variable frame size: hard to manage
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Figure 14.40: Multiplexing using different frame size
14.74
Figure 14.41: Multiplexing using cells
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Figure 14.42: ATM multiplexing
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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.
14.77
Figure 14.43: Architecture of an ATM network
14.78
Figure 14.44: TP, VPs, and VCs
TP: Transmission Path: physical connection between an endpoint and a switch or between two switchesVP: Virtual PathVC: Virtual Circuit
14.79
Figure 14.45: Virtual connection identifiers in UNIs and NNIs
14.80
Figure 14.46: An ATM cell
14.81
Figure 14.47: Routing with a switch
14.82
Figure 14.48: ATM layers
14.83
Figure 14.49: AAL5