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To: Boplicity who wrote (7287)	4/4/1999 12:16:00 PM
From: Frank A. Coluccio	Read Replies (1) \| Respond to of 29970

Greg, re: the limits of a cable tv system's bandwidth delivery. I don't know the limits in precise terms. Actually, this is an arbitrary thing, to a great extent. The variables would be the length of the coaxial section to the home (10 meters? 200 m?), the overall system loss budget (a function of design, resulting from many tradeoff analyses) and a host of rcl (resistive/capacitive/inductive) parameters governed by traditional impedance metrics. The resulting bit rate would then depend on other variables, dependent on modem modulation schemes and error tolerances. The highest universally usable frequency range appears to have settled in at approximately 1 GHz for commonly accepted distances to the residence, using ordinary coax in the last section, and that is a shared spectrum that is used by both program video and all other services, both now and into the future. If this entire spectrum were devoted solely to digital data, then I could see the bit rate reaching >16 or 32 Gb/s. The foregoing assumes a high bit-to-hertz encoding ratio resulting from an efficient modulation and encoding scheme. But to settle on a universally meaningful bit rate would require some compromises, in order to take into account worst case distances (from the remote field node to the home). In other words, you wouldn't want a condition where some homes were able to receive 64 Gb/s while others could only get 2 Gb/s. Such is the result of fairness rules that goes along with public network architecture and design. This principle has been violated to a great extent (although there are some exceptions) by the telcos, as they unleash their variable speed dsl services. [BEGIN SIDEBAR] The latter has been a point of great anguish for the incumbent telcos, since they are loathe to administer variable anythings. If you think about the scale of their operations, there are some good reasons for this, or at least reasons why one wouldn't punish them unmercifully. The fact that they are willing to do it at all at this time is a sign of desperation, IMO, and not something that would follow their divine law. Their real last mile architecture, which centers on passive optical network (PON) elements, still languishes on their drawing boards for all practical purposes. What I'm referring to is their full service area network (FSAN) concept, one which has been discussed here and in the last mile thread many times. Whether or not this FSAN architecture will ever come to pass will depend on the outcome of the latest competitive disruptions to their plans. These are, namely, the progress being made by the cablecos, and the new competitive data carriers' (DLECs') moves into their territories (Rythyms, Covad, Northpoint, MCI's OnNet, ATT's INC, FON's ION, and a host of smaller ISPs and ITSPs who are all working to become next generation telcos).[END SIDEBAR] The portion that could conceivably be used by interactive two-way (albeit asymmetric) services is small, in comparison, probably less than 100 Mz cumulative. >DSL can be applied to cable. Is that correct? < Some attributes of DSL are shared by cable modem delivery, particularly that of asymmetry, if you want to consdier the ADSL variant. For example, cable modem might allow 10 Mb/s downstream and a small fraction of that rate, say 2 Mb/s, in the upstream. ADSL does something similar by allowing 1.5 Mb/s or 7.1 Mb/s in the downstream, and 256 kb/s, or 1.7 Mb/s, respectively, in the upstream. But to say that DSL principles at the baseband level are used here is stretching it, IMO. I suppose that it would depend on your point of reference and where you want to draw the line in making the distinction. I've learned during more than 30 years of experience [sometimes the hard way] to never say never... although I've not seen this one yet. I've also read where DSL technologies are employed in some wireless techs. Again, that would be stretching it, by any measure, and would largely depend on the rules of definition and the semantics at play. Frank_C.