🚀 go-pugleaf

[POSTED TO comp.dcom.modems.cable; PLEASE REPLY THERE]

In <95sflb$8at@nfs0.sdrc.com>, scjones@thor.sdrc.com (Larry Jones)
wrote:

>John Navas (spamfilter@navasgrp.dublin.ca.us) wrote:
>>
>> On cable, A-Z can all be greatly degraded because of heavy (rather than
>> typical) upstream use by Y and Z, excessive demand for available
>> upstream by A-X, or some combination of both.
>
>I think you're being unduely pessimistic (or do you know something I
>don't?).  You seem to be assuming that the CMTS will allocate upstream
>minislots on a first-come first-served basis, but if I were writing the
>code, I'd certainly use a priority-based scheme where small requests
>take precedence over large requests.

I think that would take (1) special code in the modem or (2) quite a bit
of FIFO buffering in the CMTS.  I see no evidence of either, either in
the specs or in the available implementations.  (The CMTS doesn't know
whether the modem wants to send an ACK or a data packet; for that
matter, the modem doesn't know either.)  More to the point, real world
behavior works as I've described.

>I'd probably also keep some rough
>usage statistics (one counter per CM) so that I could give precedence to
>low bandwidth users.  With that kind of a system, heavy upstream usage
>by Y and Z would affect only them, not A-X.

To my knowledge, there is no such precedence.  In the same class of
service, the CMTS gives equal priority to all modems.  Check the specs
and the available documentation.  I'd be interested in anything more
than speculation to the contrary.

You could make the same argument about DSLAM's, routers, and whatnot,
but then there wouldn't be any such problem, and there definitely are
such problems.

-- 
Best regards,
John Navas     <http://navasgrp.home.att.net/>
     CABLE MODEM/DSL GUIDE:  <http://Cable-DSL.home.att.net/>