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DSL Physical layer overview

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m_ratheesh_k

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dsl physical layer

Hi firends,
can any one pls post information on DSL standard PHYsical description adn about Different DSL standards.

Thanks
MRK
 

amihomo

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dsl transmission layers

Hi

OFDM is adopted as the standard for transmission of data (PHY layer), and is refered to as DMT (Discrete Multi-Tone) . Several varieties of DSL exist,differing primarily in the bit rates carried and the set of subscriber lines over which satisfactory performance is achieved.

DSL Varieties

HDSL (High bit-rate DSL) - is the earliest variation of DSL to be used for wideband digital transmission within a corporate site and between the telephone company and a customer. The main characteristic of HDSL is that it is symmetrical: an equal amount of bandwidth is available in both directions. For this reason, the maximum data rate is lower than for ADSL. HDSL can carry as much on a single wire of twisted-pair as can be carried on a T1 line in North America or an E1 line in Europe (2,320 Kbps).

SHDSL can deliver 192K bit/sec over 40,000 feet of wire under ideal conditions, more than twice the effective range of other DSL flavors.

SHDSL is a variant of the technology behind two-wire, high-bit-rate DSL (HDSL2), which is a replacement for T-1 circuits, delivering a full 1.5M bit/sec bandwidth over just two wires rather than four. Whereas HDSL2 will only operate at 15M bit/sec, SHDSI's rate can be adjusted as high as 23M bit/sec, depending on the distance.


IDSL (ISDN DSL) - is somewhat of a misnomer since it's really closer to ISDN data rates and service at 144 Kbps than to the much higher rates of ADSL. IDSL is usually not sold by ADSL providers, is symmetric ("duplex"), with the biggest advantage being the distance it can travel (5-6 miles). Similar to ISDN (128 Kbps) but uses the control channel to increase data rates to 144 Kpbs.

RADSL (Rate-Adaptive DSL) - is an ADSL technology from Westell in which software is able to determine the rate at which signals can be transmitted on a given customer phone line and adjust the delivery rate accordingly. Westell's FlexCap2 system uses RADSL to deliver from 640 Kbps to 2.2 Mbps downstream and from 272 Kbps to 1.088 Mbps upstream over an existing line.

SDSL (Single-line DSL) - is apparently the same thing as HDSL with a single line, carrying 1.544 Mbps (U.S. and Canada) or 2.048 Mbps (Europe) each direction on a duplex line. It is considered to be the "business grade" DSL because of its symmetric speeds. SDSL is slower than ADSL but usually marketed with Service Level Agreement (SLA) such as the network will be guaranteed up for 99.5%, and there will be a 24-hour response time for every problem.

UDSL (Unidirectional DSL) - is a proposal from a European company. It's a unidirectional version of HDSL.

VDSL (Very high data rate DSL) - is a developing technology that promises much higher data rates over relatively short distances (between 51 and 55 Mbps over lines up to 1,000 feet or 300 meters in length). It's envisioned that VDSL may emerge somewhat after ADSL is widely deployed and co-exist with it. The transmission technology (CAP, DMT, or other) and its effectiveness in some environments are not yet determined. A number of standards organizations are working on it.

xDSL - Refers collectively to all types of Digital Subscriber Lines, the two main categories being ADSL and SDSL.

x2/DSL - is a planned modem from 3Com and US Robotics that supports 56 Kbps modem communication but is upgradable through new software installation to ADSL when it becomes available in the user's area. 3Com calls it "the last modem you will ever need."



regards
 

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