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Splitting the Signal and DSL Equipment
The CAP System |
There are two competing and incompatible standards for ADSL. The official ANSI standard for ADSL is a system called discrete multitone, or DMT. According to equipment manufacturers, most of the ADSL equipment installed today uses DMT. An earlier and more easily implemented standard was the carrierless amplitude/phase (CAP) system, which was used on many of the early installations of ADSL. |
The DMT System |
DMT also divides signals into separate channels, but doesn't use two fairly broad channels for upstream and downstream data. Instead, DMT divides the data into 247 separate channels, each 4 KHz wide. |
Filters |
CAP and DMT are similar in one way that you can see as a DSL user. |
ADSL uses two pieces of equipment, one on the customer end and one at the Internet service provider, telephone company or other provider of DSL services. At the customer's location there is a DSL transceiver, which may also provide other services. The DSL service provider has a DSL Access Multiplexer (DSLAM) to receive customer connections. |
Most residential customers call their DSL transceiver a "DSL modem." The engineers at the telephone company or ISP call it an ATU-R. Regardless of what it's called, it's the point where data from the user's computer or network is connected to the DSL line. |
The DSLAM |
The DSLAM at the access provider is the equipment that really allows DSL to happen. A DSLAM takes connections from many customers and aggregates them onto a single, high-capacity connection to the Internet. DSLAMs are generally flexible and able to support multiple types of DSL in a single central office, and different varieties of protocol and modulation -- both CAP and DMT, for example -- in the same type of DSL. In addition, the DSLAM may provide additional functions including routing or dynamic IP Address assignment for the customers. The DSLAM provides one of the main differences between user service through ADSL and through cable modems. Because cable-modem users generally share a network loop that runs through a neighborhood, adding users means lowering performance in many instances. ADSL provides a dedicated connection from each user back to the DSLAM, meaning that users won't see a performance decrease as new users are added -- until the total number of users begins to saturate the single, high-speed connection to the Internet. At that point, an upgrade by the service provider can provide additional performance for all the users connected to the DSLAM. Thanks & Regards, "Remember Me When You Raise Your Hand For Dua" Raheel Ahmed Khan System Engineer send2raheel@yahoo.com send2raheel@engineer.com sirraheel@gmail.com send2raheel (skype id) My Blog Spot http://raheel-mydreamz.blogspot.com/ http://raheeldreamz.wordpress.com/ My Face book pages http://www.facebook.com/pages/My-Dreamz-Rebiuld-our-nation/176215539101271 @[176215539101271:0] http://www.facebook.com/pages/Beauty-of-islam/223983470988333?sk=wall @[223983470988333:0] http://www.facebook.com/pages/Health-is-wealth/289486761065829?sk=wall @[289486761065829:0] |
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