1. ADSL
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2. Overview
 Asymmetric Digital Subscriber Line
 A high speed digital communication
 Converts Cu twisted pair TP line in
POTS into high speed communication
 Designed for residential users
 Like a 56K modem, provides a higher
speed in the downward direction than in
upstream direction
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3. Objective
 To be able to work at a larger bit rate
with more reliability
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4. Basic Requirements
 Full use of Cu line frequency spectrum
 Advanced coding & decoding methods
 Ability to work simultaneously with POTS
on same Cu line
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5. Technologies used
 Discrete Multi tone –
 Divides the frequency range of 1.104 MHz into 256 sub-
frequencies of 4.312 kHz bandwidth
 Each sub-frequency is an independent channel & has its own
stream of signals
 Channel 0 is reserved for voice communication
 Channels 1 to 5 are not used & provide a gap between voice
and data communication
 Channels 6 to 30 are used for upstream data transfer & control.
One channel for control and 24 channels for data transfer
 Channels 31 to 255 are used for downstream data transfer &
control. One channel for control & 224 channels for data
transfer
 Code & Error Correction
 Framing & Scrambling
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6. More about ADSL
 Provides both normal TP and high-speed digital
transmissions on an existing TP line
 Twisted-pair Cu wire carries:
 Normal TP communication in range of 0 to 3.4 kHz
 Data upload range of 30 to 138 kHz
 Data download range of up to 1104 kHz
 It minimizes crosstalk signals:
 Transmits from users in lower range (30 to 138 kHz) because
lower frequencies have less attenuation
 ADSL transceiver sends data at high frequencies, generates a
very little crosstalk because of a very strong outgoing signal
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7. More about ADSL (continued)
 Due to difference in data-carrying capacities, it
is called Asymmetric
 Other variants: HDSL, SDSL, VDSL
 HDSL: Less susceptible to attenuation, data rate – 1.5 to 2
Mbps up to 12,000 ft., uses two twisted pair cables, full-duplex.
 SDSL: One twisted-pair version of HDSL, Full-duplex, used in
businesses.
 VDSL: Uses coaxial, fiber-optic or twisted-pair cable for very
short distances. Range from 25-55 Mbps Uplink and 3.2 Mbps
downlink.
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8. Advantages of ADSL
 Cost-effectiveness
 Low equipment installation and usage costs
 Speed
 High data transfer speed for Broadband-quality bi-
directional video conferencing
 Ease of use
 Reliability
 Competitive
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9. Questions
 Read about DSL technologies
 Why ADSL is better than cables?
 Define techniques similar to ADSL.
 Give limitations of Cu lines.
 Study the architecture of an ADSL
modem.
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