9.1 Chapter 9 Using Telephone and Cable Networks for Data Transmission Copyright © The McGraw-Hill...

transcript

Chapter 9

Using Telephoneand Cable Networks

for Data Transmission

9-1 TELEPHONE NETWORK9-1 TELEPHONE NETWORK

Telephone networks use circuit switching. The Telephone networks use circuit switching. The telephone network had its beginnings in the late telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the 1800s. The entire network, which is referred to as the plain old telephone systemplain old telephone system ( (POTSPOTS), was originally an ), was originally an analog system using analog signals to transmit voice.analog system using analog signals to transmit voice.

Major ComponentsLATAsSignalingServices Provided by Telephone Networks

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

Switched Network

Circuit Switching

uses a dedicated path between two stations has three phases

establish transfer disconnect

inefficient channel capacity dedicated for duration of

connection if no data, capacity wasted

set up (connection) takes time once connected, transfer is transparent

Public Circuit Switched Network

private branch exchange (PBX)

Circuit Establishment

Circuit Switch Elements

Blocking or Non-blocking

blocking network may be unable to connect stations

because all paths are in use used on voice systems

non-blocking network permits all stations to connect at once used for some data connections

Figure 9.1 A telephone system

Endoffices

Local loop

Tandemoffices Regional offices

• • •

Figure 9.2 Switching offices in a LATA (local-access transport area)

Intra-LATA (local access transport area) services are provided by local exchange

carriers (LECs). Since 1996, there are two

types of LECs: incumbent local exchange carriers and competitive

local exchange carriers.

IXC (Interexchange carrier, long distance company)

Figure 9.3 Point of presences (POPs)

Normally digitized data

Pop: point of presence

The tasks of data transfer and signaling are separated in modern telephone

networks: data transfer is done by one network, signaling by another.

Traditional Circuit Switching

Figure 9.4 Data transfer and signaling networks

Packet-switch

Packet-switch or circuit-switch

Figure 9.5 Layers in SS7 (signaling system seven)

9-2 DIAL-UP MODEMS9-2 DIAL-UP MODEMS

Traditional telephone lines can carry frequencies Traditional telephone lines can carry frequencies between 300 and 3300 Hz, giving them a bandwidth of between 300 and 3300 Hz, giving them a bandwidth of 3000 Hz. All this range is used for transmitting voice, 3000 Hz. All this range is used for transmitting voice, where a great deal of interference and distortion can where a great deal of interference and distortion can be accepted without loss of intelligibility.be accepted without loss of intelligibility.

Modem StandardsTopics discussed in this section:Topics discussed in this section:

Digital Data, Analog Signal: Modulation Techniques

Figure 9.6 Traditional Telephone line bandwidth

Modern phone line has higher bandwidth

Modemstands for modulator/demodulator.

Figure 9.7 Modulation/demodulation

TELCO: telephone company (unnecessary acronyms! I think)

Quadrature Amplitude Modulation QAM used on asymmetric digital

subscriber line (ADSL) and some wireless combination of ASK and PSK logical extension of QPSK send two different signals simultaneously

on same carrier frequency use two copies of carrier, one shifted 90°

each carrier is ASK modulated two independent signals over same medium demodulate and combine for original binary

output

QPSK Illustration

This figure copied from wikipedia

V-series standard

Modulation Data Rate Baud Rate

V.32 32-QAM 9600 bps 2400 baud Only 4 bits represent data

V.32 bis 128-QAM 14,400 bps 2400 baud Only 6 bits represent data

V.34 bis M-QAM 28,800-33,600 bps

V.90 M-QAM 56 Kbps (downstream)33.6 Kbps (upstream)

V.92 M-QAM 56 Kbps (downstream)48 Kbps (upstream)

A modem adjusts its speed

Modem Standards

Figure 9.9 Uploading and downloading in 56K modems

SNR explains why upload speed is higher

9-3 DIGITAL SUBSCRIBER LINE9-3 DIGITAL SUBSCRIBER LINE

After traditional modems reached their peak data rate, After traditional modems reached their peak data rate, telephone companies developed another technology, telephone companies developed another technology, DSL, to provide higher-speed access to the Internet. DSL, to provide higher-speed access to the Internet. Digital subscriber lineDigital subscriber line ( (DSLDSL) technology is one of the ) technology is one of the most promising for supporting high-speed digital most promising for supporting high-speed digital communication over the existing local loops. communication over the existing local loops.

ADSLADSL LiteHDSLSDSLVDSL

ADSL is an asymmetric communication technology designed for residential

users; it is not suitable for businesses.

The existing local loops (twisted-pair lines) can handle bandwidths up to

1.1 MHz.

ADSL is an adaptive technology. The system uses a data ratebased on the condition of

the local loop line.

Figure 9.10 Discrete multitone technique (QAM + FDM)

Figure 9.11 Bandwidth division in ADSL

Figure 9.12 Customer site: ADSL modem

Splitter and data line need installation (maybe expensive)

Figure 9.13 telephone company site

Table 9.2 Summary of DSL technologies

ADSL Lite: does not need additional installation from telephone company

9-4 CABLE TV NETWORKS9-4 CABLE TV NETWORKS

The The cable TV networkcable TV network started as a video service started as a video service provider, but it has moved to the business of Internet provider, but it has moved to the business of Internet access. In this section, we discuss cable TV networks access. In this section, we discuss cable TV networks per se; in Section 9.5 we discuss how this network can per se; in Section 9.5 we discuss how this network can be used to provide high-speed access to the Internet.be used to provide high-speed access to the Internet.

Traditional Cable NetworksHybrid Fiber-Coaxial (HFC) Network

Figure 9.14 Traditional cable TV network

Communication in the traditional cable TV network is unidirectional.

Figure 9.15 Hybrid fiber-coaxial (HFC) network

Communication in an HFC cable TV network can be bidirectional.

9-5 CABLE TV FOR DATA TRANSFER9-5 CABLE TV FOR DATA TRANSFER

Cable companies are now competing with telephone Cable companies are now competing with telephone companies for the residential customer who wants companies for the residential customer who wants high-speed data transfer. In this section, we briefly high-speed data transfer. In this section, we briefly discuss this technology.discuss this technology.

BandwidthSharingCM and CMTSData Transmission Schemes: DOCSIS

Figure 9.16 Division of coaxial cable band by CATV

Downstream data are modulated using the 64-QAM modulation technique.

The theoretical downstream data rateis 30 Mbps.

Upstream data are modulated using the QPSK modulation technique.

This figure copied from wikipedia

The theoretical upstream data rate is 12 Mbps.

Sharing: Upstream sharing

The upstream bandwidth is 37 MHz. There are six 6-MHz channels

available. How can the channels be shared in an

area with 1000,2000 or even 200,000 subscribers?

Using FDM/timesharing. Subscribers have to contend for the

channels with others.

Sharing: Downstream sharing The downstream band has 33

channels of 6 MHz. We have a multicast situation. If there is data for any of subscribers

in the group, the data are sent to that channel.

Figure 9.17 Cable modem (CM)

Figure 9.18 In cable company: Cable modem transmission system (CMTS)

Data Transmission Schemes: Data Over Cable System Interface Specification

Defines all the protocols necessary to transport data from a CMTS to a Cable Modem.

Upstream Communication CM checks for specific packets sent by CMTS. The CMTS sends a packet to CM, defining its

allocated downstream and upstream channels. The CM starts ranging process (to determine

the distance for synchronization).

Data Transmission Schemes: Data Over Cable System Interface Specification

The CM sends a packet to the ISP, asking for the IP address.

The CM and CMTS exchange some packets to establish security parameters.

The CM sends its unique identifier to the CMTS.

Upstream communication can start in the allocated upstream channel.

Data Transmission Schemes: Data Over Cable System Interface Specification (DOCSIS) Downstream Communication

No contention because only one sender. The CMTS sends the packet with the

address of the receiving CM, using the allocated downstream channel.

9.1 Chapter 9 Using Telephone and Cable Networks for Data Transmission Copyright © The McGraw-Hill...

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