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Chapter 9 Using Telephone and Cable Networks for Data Transmission

1. Telephone Network

2. Dial-up Modems

3. Digital Subscriber Line

4. Cable TV Networks

5. Cable TV for Data Transfer

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Telephone Companies: Brief History

• Before 1984– Almost all services are provided by AT&T Bell System

– In 1984, AT&T was broken into

• AT&T long Lines

• 23 BOCs(Bell Operating Companies)

• BOCs are grouped together to several RBOCs

• Between 1984 and 1996– Divided into more than 200 LATAs (Local Access Transport Area

s)

• After 1996– Any companies can provide any services

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A Telephone System

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LATAs

• A LATA can be a small or large metropolitan area• Intra-LATA services are provided by local exchan

ge carriers– ILEC (Incumbent Local Exchange Carriers)

– CLEC (Competitive Local Exchange Carriers)

• Inter-LATA services are handled by IXCs (Inter-Exchange Carriers)– Called long-distance companies

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Switching Offices in a LATA

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POP (Point of Presence)

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Signaling

• In-band signaling : the same circuit used for both signaling and voice communication

• Out-of-band signaling• The task of data transfer and signaling are separated in

modern telephone network• Signaling system are required to

– Providing dial tone, ring tone, and busy tone– Transferring telephone numbers between offices– Maintaining and monitoring the call– Keeping billing information– Maintaining and monitoring the status of the telephone network

equipment– Providing other functions such as caller ID, voice mail, and so on

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Data Transfer and Signaling Networks

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Layers in SS7(Signaling System 7)

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Telephone Network Services

• Analog services– Analog switched services

• Dial-up service

• 800 service, 900 service

• WATS (wide-area telephone service)

– Analog leased service: called a dedicated line

• Digital service– Switched/56 service

– Digital data service: digital leased line

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Dial-Up Modems

• Data signals require a higher degree of accuracy to ensure integrity

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Modem

• Modem stands for modulator/demodulator

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Modem Standards

• V-series standards by ITU-T– V.32 : Trellis-coded modulation: 32-QAM (4 data bits

and a redundant bit for error detection) 9,600 bps

– V.32bis : 128-QAM (7 bits/baud with 1 bit for error control) 14,400 bps

– V.34bis : 28,800 bps with a 960-point constellation and 33,600bps with a 1664-point constellation

– V.90: Upload: 33.6 kbps, download: 56 kbps

– V.92: Upload: 48 kbps, download: 56 kbps

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V.32 and V.32bis

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V.90: 56K Modem

• Traditional modems have a data rate limitation of 33.6 kbps by Shannon capacity

• Uploading : 33.6 kbps• Downloading: 56 kbps

– 8000 samples x 7 bit– 1 bit for control

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ADSL

• Asymmetrical Digital Subscriber Line• ADSL is an asymmetric communication

technology designed for residential users; it is not suitable for businesses

• The existing local loop can handle bandwidths up to 1.1 MHz

• ADSL is an adaptive technology. The system uses a data rate based on the condition of the local loop line.

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DMT (Discrete Multitone Technique)

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Bandwidth Division in ADSL

• There is no set way that the bandwidth is divided

• Upstream

– 24 channels x 4 kHz x 15 bits/Hz = 1.44 Mbps

• Downstream

– 224 channels x 4 kHz x 15 bits/Hz = 13.4 Mbps

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DSL: Actual Bit Rate

• Because of the high signal/noise ratio• Upstream

– Normally below 500 kbps

• Downstream– Normally below 8 Mbps

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Customer Site: ADSL Modem

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Telco Site: DSLAM

• Digital subscriber line access multiplexer

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Other DSL Technologies: xDSL

• HDSL (High-bit-rate DSL)

– Designed as an alternative to the T-1 line (AMI encoding)

– 2B1Q encoding used for less susceptible to attenuation

– Up to a distance 12,000 ft without repeaters

– Two twisted pairs for full-duplex transmission

• SDSL (Symmetric DSL)– One twisted pair version of HDSL– 768 kbps in each direction, symmetric communication

– Send and receive data in large volumes in both directions

• VDSL (Very-high-bit-rate DSL): Alternative approach to ADSL

– Coaxial, fiber-optic, or twisted-pair cable for short distances

– Uses DMT with 25-55 Mbps (downstream) and 3.2 Mbps (upstream)

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Summary of DSL Technologies

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Traditional Cable TV Network

• Started to distribute video signals to locations with poor or no reception in the late 1940s: Unidirectional

• It was called Community Antenna TV

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HFC (Hybrid Fiber Coaxial) Network

• RCH (Regional Cable Head) feeds the distribution hubs

• Fiber node splits the signal to each coaxial cable

• Communication in an HFC network can be bidirectional

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Coaxial Cable Bands

• Video band: 6 MHz per TV channel

• Downstream data band: 64-QAM (or possibly 256-QAM)

– Theoretical rate is 30 Mbps (6 MHz/sec x 5 bits/Hz)

• Upstream data band: QPSK

– Theoretical rate is 12 Mbps (6 MHz/sec x 2 bits/Hz)

• Both upstream and down stream bands are shared by the subscribers

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CM (Cable Modem)

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CMTS (Cable Modem Transmission System)

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Data Transmission Schemes: DOCSIS

• Standard for data transmission over a HFC network by Multimedia Cable Network System (MCNS)– Data Over Cable System Interface Specification

(DOCSIS) : defines all the protocols to transport data from CMTS to a CM