DSL PPT

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DIGITAL SUBSCRIBERLINE

PREPARED BY-

DEEPAK MEHTANI11082365

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Digital Subscriber Line (DSL) is a family of technologiesthat provides digital data transmission over the wires of a

local telephone network. DSL originally stood for digitalsubscriber loop The data throughput of consumer DSLservices typically ranges from 384 Kbit/s to 20 Mbits/s inthe direction to the customer, depending on DSLtechnology, line conditions, and service-levelimplementation digital subscriber line access multiplexer(DSLAM) protocols used in connection such as DHCP orPPPoE DSL technology require installation of appropriatefilters to separate Asynchronous Transfer Mode (ATM)layer over the low-level bitstream layer to enable theadaptation of a number of different technologies over the

same link.  

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DSLBLOCK

DIAGRAM

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Asymmetrical DSL (ADSL)

ADSL divides up the available frequencies in aline on the assumption that most Internet userslook at, or download, much more informationthan they send, or upload.

Under this assumption, if the connection speedfrom the Internet to the user is three to fourtimes faster than the connection from the userback to the Internet, then the user will see the

most benefit (most of the time). 

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Asymmetrical DSL (ADSL)

ADSL is an adaptive technology.

The system uses a data rate based on the 

condition of the local loop line.

Speed:

Most existing local loops can handlebandwidths up to 1.1 MHz.

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ADSL Modem

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Two standards for ADSL

1. Discrete multitone (DMT)

2. Carrierless amplitude/phase(CAP)

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CAP - three distinct bands:

1. Voice channel - 0 to 4 KHz 

2. Upstream channel - 25 and 160 KHz 

3. Downstream channel - 1.5 MHz 

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Carrierless amplitude/phase (CAP)

Advantage:

Minimizes the possibility of

interference between the channels onone line, or between the signals on

different lines 

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Discrete multitone (DMT)

Constantly shifts signals betweendifferent channels, searching for the bestchannels for transmission and reception 

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Discrete multitone (DMT)

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Asymmetrical DSL (ADSL)

ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses.

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Distance Limitations

ADSL is a distance-sensitive technology 

The limit for ADSL service is 18,000 feet (5,460meters)

At the extremes of the distance limits, ADSLcustomers may see speeds far below thepromised maximums

customers nearer the central office have fasterconnections and may see extremely highspeeds

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OTHER TYPES OF DSL:

Symmetric DSL (SDSL)

High-bit-rate DSL (HDSL)

Very high bit-rate DSL (VDSL)

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Symmetric DSL (SDSL)

Used mainly by small businesses & residential

areas

Bit rate of downstream is higher than upstream

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High-bit-rate DSL (HDSL)

Used as alternative of T-1 line

Uses 2B1Q encoding

Less susceptible to attenuation at higher

frequencies

Unlike T-1 line (AMI/1.544Mbps/1km), it canreach 2Mbps @ 3.6Km

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Very high bit-rate DSL (VDSL)

Uses DMT modulation technique

Effective only for short distances(300-1800m)

Speed:

downstream : 50 - 55 Mbps

upstream : 1.5-2.5 Mbps

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Question!

Distance is a limitation for DSL, why it's not

also a limitation for voice telephone calls ?

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Answer!

The answer lies in small amplifiers called

loading coils that the telephone companyuses to boost voice signals

these loading coils are incompatible with ADSLsignals, so a voice coil in the loop betweenyour telephone and the telephone company'scentral office will disqualify you from receiving

ADSL.

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ADSL :customer disqualifying factors

Bridge taps - These are extensions, between you and thecentral office, that extend service to other customers. Whileyou wouldn't notice these bridge taps in normal phoneservice, they may take the total length of the circuit beyondthe distance limits of the service provider.

Fiber-optic cables - ADSL signals can't pass through theconversion from analog to digital and back to analog thatoccurs if a portion of your telephone circuit comes throughfiber-optic cables.

Distance - Even if you know where your central office is

(don't be surprised if you don't -- the telephone companiesdon't advertise their locations), looking at a map is noindication of the distance a signal must travel between yourhouse and the office.