[NCLUG] DSL Throttling or General Congestion?

Stephen Warren swarren at wwwdotorg.org
Tue Nov 21 11:56:25 MST 2006


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Michael Milligan wrote:
> F.L. Whiteley wrote:
>> Hi Onyx,
>>
>> Hope you're well and best of the season.
>>
>> I agree, nothing of the sort of FRII.  I may have a chance to look at
>> this MSN/Qwest DSL account again before long and take some tools and
>> links to test it out.  It's close to my location and across the street
>> from the 256k customer.  So far, no one else is confirming, so it may
>> have been an anomaly.
> 
> I can confirm issues with Qwest DSL where I am located (North of Ft.
> Collins) due to congestion periods which happen every damn day starting
> early evening and lasting till early morning, sometimes late into the
> morning the next day.  I have been tracking this with smokeping for many
> months and bandwidth tests during the congestion times confirm the
> available bandwidth shrinks from 160Kb/s down to 30-50Kb/s range with
> delay jumping from 30ms to 250ms to my first-hop gateway.  It really
> sucks bad some nights.  ISP (foreThought.net) says it's Qwest's problem.

That (being Qwest's problem) doesn't sound likely.

With alternate ISPs, I *believe* that your phone line goes into an ATM
switch at the nearest CO (central office), and that ATM line is then
routed, in isolation, to the ISP. Only then does the ATM traffic get
unpacked into potentially other transport technologies.

The thing about ATM is that it's time division multiplexing, so there's
an assigned fixed-bandwidth link all the way from your DSL modem at home
all the way to the ISP.

As such, there's no opportunity for any kind of modem-modem interference
(or anything else) until your traffic actually gets to the ISP's own
equipment.

I suppose it's possible for the ATM session to be terminated directly in
the CO, and then to have, say, a GigE backhaul to the ISP, but I don't
*think* that's typical. Even in that situation, though, I believe the
ISP would have to manage the ATM->GigE router, because the ISP assigns
line bandwidth, authentication information, etc.

Of course, I'm not a telco insider, so I may be way off base here, but
this should give you something to ask Forethought!
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