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To: cgl69 who wrote (6022)	3/5/1999 9:08:00 PM
From: Frank A. Coluccio	Read Replies (2) \| Respond to of 29970

All access technologies will encounter sharing and contention dynamics beyond the central office device (the head end or the DSL collection and distribution unit) if the cloud is IP based, until prioritization schemes are instituted on the 'net. On Cable, most residential drops are shared to the head end as well, as there is often one big collision domain that must be negotiated. There are exceptions to this. I believe that COM21 allows for a certain degree of dedicatedness in its design, through an ATM approach. DSLs are dedicated when they employ DSLAMs between the residence and the Central Office. DSLAMs use deterministic protocols on the backplane (such as ATM) and avail themselves to virtual circuits. DSL can also be shared between the CO device and the residential pool, as in the case where the CO device is an Access "concentrator" which employs a collision-based hub, instead of ATM. This aspect of shared vs. collision-based attributes for DSL and cable modem are often over-generalized by just about everyone, to the point where the distinctions I've cited are seldom made or understood. But they exist, nonetheless. Most Bells and other large ILECs, and even some of the larger DLECs will use DSLAMs of the deterministic type (Bellcore blueprint at work here). Many of the startups and ISPs-wannabe-telcos are electing to use the collision domain types to stay on the cheap (and to avoid the seeminly arcane adminstrative demands of ATM, at the same time). The thing to keep in mind here is that all DSL access and concentration devices are not equal.