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Cable Modem Primetime Slowdown - Myth or Reality?

Posted by Cliff on from the finding-the-bottleneck dept.

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?"

2 of 43 comments (clear)

  1. Re:Little bit of each by AtrN · · Score: 5, Funny

    the best they claim for me is 128Mbps either direction. All that for $50 a month


    Damm, there's that "post from the future" bug again.
  2. Any internet technology can be oversubscribed by hamjudo · · Score: 5, Informative
    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.