Darell, many, but not all DSLAMs, work the way you stated. Some are contention based in the backplane, while others are deterministic like you say. The units that conform to the original Bellcore standards operate as DSL access multiplexers, or DSLAMs, and where these are concerned I agree with you fully.
The other breed, called DSL Access Concentrators, or DSLACs, use collision domain principles in order to cut down on cost, and to more readily facilitate a hand off to a router. In contrast, DSLAMs use ATM chiefly on their back ends.
As a general rule, ILECs and some of the newer nationwide DLECs who are selling DSL services will go with the DSLAMs which uses the ATM fabric in the edge.
Smaller ISPs and some regional aggregators may elect, more often than not for economic reasons mostly, to go with concentrators.
Regards, Frank Coluccio |
