Re: [aclug-L] Cable Modems

[Tim Buller <buller@xxxxxxxxxxxxxx>]

On Wed, 23 Dec 1998, Bob Deep wrote:

> There is no real way for them to know if you are masquarading, it all
> looks like one machine to them. 

A cable ISP can in fact sniff the network for NAT/IPMASQ packets. Whether
they will actually go through the trouble to do that is another question.

A little later on Wed, 23 Dec 1998, Bob Deep wrote:

> Upon close reading of the advertisments... You get to share the 42Mbs
> with everybody on your segment, so as they get more and more subscribers
> online, the available bandwidth will drop accordingly.  So just 5 folks
> running at 10Mbs will swamp the carrier you are assinged. 

I assume when the Multimedia web pages say "standards based" cable modems
they mean the DOCSIS standard. My understanding of DOCSIS is cursory, but
I believe that it uses a Time-Division Multiplexing scheme for all nodes
on a data channel. By allocating units of time, the cable ISP can control
the amount of bandwidth available to each node. The concept is that if you
want/need more BW, you can pay for it. This also imposes a hard BW limit
on each node. One of the biggest advantages of the TDM scheme is that it
effectively eliminates collisions in a similar manner to a token-ring
network. I'm not sure if the upstream data flow work in this way too, of
if it is only the downstream. Or I may be completely off about the whole
thing...

At any rate, in a market the size of Wichita, I think the bottleneck will
immediatly lodge in  the cable ISPs upstream connection, unless they have
a pretty goddamn big pipe. In Lawrence, the cable ISP has 3000-5000 users
(I believe) with 2 full T1s and they saturate from time to time.

        Tim

====
Tim Buller                                       buller@xxxxxxxxxxxxxx
Systems Specialist                               Office: Snow Hall 643
Department of Mathematics                          Voice: 785-864-7311
University of Kansas, Lawrence, KS 66045             Fax: 785-864-5255

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lK[d2%Sa2/d0$^Ixp"|dc`;s/\W//g;$_=pack('H*',/((..)*)$/)

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