Cable Modem Primetime Slowdown - Myth or Reality?

The Llama King asks: "SBC (SWBell, Pacbell, etc.) is whacking away at Time Warner cable in our area, running DSL ads that make fun of prime-time cable modem slowdown. And Time Warner-Houston/RoadRunner does seem to be having a problem in the past month with nasty ping times between 8 pm - midnight Central time (traces submitted to internal RoadRunner news groups show the problem appears to be a pair of routers at the gateway to one of several backbones). While this problem is recent, it begs the question - are prime-time cable slowdowns real or a myth? Can a well-configured cable modem network avoid the congestion SBC pokes fun at in their commercials, or is it inevitable? What are Slashdot users seeing?"

Comments

Charter In Auburn, MA

[haplo21112]

Charter Cable here in Auburn Worcester Area has "ever changing pings". For sometime now I have never been able to get anything even resembling a consistent ping time or download rate. Somedays the connection flys the next its barely faster than a 56K modem. During the whole "Code Red" thing it was just sad, the light on my linksys router, for activity was just solid didn't blink at all. I called them several times and asked them to look into the reasons why their network was in such a state. I telecomute into my compant from time to time so this period was esspecially annoying. I am still monitoring several Code Red, Nimda, and related virus'es a day knowcking on the door. I guess in the end the moral of this story, the network only as good as those who run it, and even less good if they never listen to the users of the network who try to tell them whats wrong.

Any internet technology can be oversubscribed

[hamjudo]

With DSL only the very first hop is dedicated to a single customer. Once your bits get to the central office, they share a pipe with other customers. If that pipe has less bandwidth than the sum total bandwidth of the individual customers, that pipe is oversubscribed. Likewise for all of the upstream pipes.

With a cable modem, the only difference is that the very first hop might also be oversubscribed.

A cable has a lot of bandwidth. That bandwidth is divided up into channels (on an NTSC analog system, channels are all 6Mhz wide, your channels may vary). Each internet cable box is assigned a channel (or set of channels, if channels only come in one size). Your next door neighbor's cable box might use a different channel, and thus not be in the same neighborhood.

Logically, a cable system is a tree, or set of trees, with the root of each tree at the cable company office, and the customers are the leaves. The thicker branches may run on fiber, they support more channels, and therefore more neighborhoods.

A wee tiny cable company may have a single T1 (1.5Mbps) line connecting to the greater internet, a large company might have several OC48 (2.5Gbps). The same is true for DSL providers.

ISP's either charge premium rates or they oversubscribe the service, or both. I don't see a primetime slowdown on my $180/month, 384K DSL line.