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To: D. Newberry who wrote (1529)	5/13/1999 2:02:00 AM
From: Frank A. Coluccio	Read Replies (1) \| Respond to of 5853

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

To: D. Newberry who wrote (1529)	5/13/1999 10:19:00 AM
From: Clarksterh	Read Replies (2) \| Respond to of 5853

Cable capacity vs DSL: Just out of curiosity I worked through some numbers. For internet traffic: 1) Assume that cable currently broadcasts to several thousand homes for each headend - call it 2500 homes per headend (a WAG). Also assume that they have 200MHz (about 30 conventional TV channels) to spare for ISP service. If you assume peak loading of 20% of homes on line of which only 10% are actually downloading at any given time that is still about 4MHz per user. (Of course not all MHz are created the same, but for back-of-the envelope purposes, ...) 2) For DSL the best rate will be less than 1.5MHz. Cable wins for internet traffic But for less bursty traffic, like video on demand: 1) Cable - same assumptions as before, but assume max usage is 35% of households and the burstiness is less. Assume that burstiness is 3 now instead of 10. Now the users each get about 700 KHz. 2) For DSL the best rate will be a little lower due to cross talk, but it will probably still be above 1MHz. Thus, DSL wins. But it should be noted that for a fairly small price cable can decrease the number of households per headend. Add an extra 2 or 3 headends and cable wins in both cases. The coax pipe is a big advantage. Note that, like you, I actually expected that the DSL would provide the higher rates until I did some calculations. FWIW Clark

To: D. Newberry who wrote (1529)	5/14/1999 12:26:00 AM
From: jack bittner	Read Replies (1) \| Respond to of 5853

your dsl/cable points are quite pertinent. i see your posts on GBLX's thread, and you mention it here admiringly. gblx is cable. is cable relatively less reliable for the long haul too?

To: D. Newberry who wrote (1529)	5/16/1999 12:38:00 PM
From: Bill Fischofer	Read Replies (1) \| Respond to of 5853

Re: Shared bandwidth This has to be one of the wider circulated myths surrounding cable. Here's the real story: The entire net is based on shared bandwidth. The only question is at what level do bottlenecks arise. Does anyone honestly believe that the average local telco switching office has sufficient bandwidth on premises to handle 1000 simultaneous DSL users? Just where does that "dedicated" DSL line terminate? The answer, obviously, is that all subscribers share bandwidth and whether that sharing takes place at a central office or is distributed throughout a cable loop is largely irrelevant. Both approaches must continually upgrade capacity as additional subscribers are added. As someone who has been using cable modem service since August 1997, I can state that I have never observed congestion which appeared to be due to local loop problems. On the contrary, once one is using broadband the congestion upstream on the various backbones becomes even more noticeable.