Re: cable guy "vapor"-izes DSL 3X cable TV troll!

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#503

From: Randy S.
Date: Sat, 03 Feb 2001 17:59

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> The upstream channel can be anywhere from 160 Kbps (200 kHz QPSK) to 10
> Mbps (3.2 MHz QAM 16).  My understanding is that 800 Khz QPSK is most
> common in practice (due to signal quality and error rate issues), giving
> an upstream channel capacity of 640 Kbps.  With 4 upstream channels per
> downstream channel, the aggregate upstream capacity would be about 2.5
> Mbps, as compared to downstream capacity of 27 Mbps.  Note that if the
> upstream saturates, the downstream rate will drop to about the same
> speed, a dramatic slowdown of about 90% (2.5 Mbps as compared to 27
> Mbps)!

Ahh, these look like much more realistic numbers than the ones I saw, thank
you.  The document I saw was quoting maximum datarates per channel, which as
you show here is 27 Mbps down and 10 Mbps up.  The up rate sounded too high
to me, and the above statement points out why. Do most cable systems use a
4:1 upstream to downstream channel ratio, and only allocate one channel for
download?

Randy S.

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<3A648E27.6A7029EF@erols.com> <20010116192016044.AAA95@adsl-209-204-185-87.sonic.net@john.navasgroup.com> <3A64B680.2A79F24D@erols.com> <3A76B6CA.73B36B26@mynetwatchman.com> <4OGd6.100$mW6.5202@typhoon.sonic.net> <3A776B57.C495242C@mynetwatchman.com> <3A77D75E.82B3CDB3@columbus.rr.com> <3A78184F.2C40E5E6@ufl.edu> <3A78327F.BDD53DB3@mynetwatchman.com> <%oXe6.200$Tf1.8852@typhoon.sonic.net>

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Subject: Re: cable guy "vapor"-izes DSL 3X cable TV troll!
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