Slashdot Mirror

← Back to Stories (view on slashdot.org)

Comcast Cheating On Bandwidth Testing?

Posted by kdawson on from the tuning-for-the-benchmark dept.

dynamo52 writes "I'm a freelance network admin serving mainly small business clients. Over the last few months, I have noticed that any time I run any type of bandwidth testing for clients with Comcast accounts, the results have been amazingly fast — with some connections, Speakeasy will report up to 15 Mbps down and 4 Mbps up. Of course, clients get nowhere near this performance in everyday usage. (This can be quite annoying when trying to determine whether a client needs to switch over to a T1 or if their current ISP will suffice.) Upon further investigation, it appears that Comcast is delivering this bandwidth only for a few seconds after any new request and it is immediately throttled down. Doing a download and upload test using a significantly large file (100+ MB) yields results more in line with everyday usage experience, usually about 1.2 Mbps down and about 250 Kbps up (but it varies). Is there any valid reason why Comcast would front-load transfers in this way, or is it merely an effort to prevent end-users from being able to assess their bandwidth accurately? Does anybody know of other ISPs using similar practices?"

14 of 287 comments (clear)

  1. This is an advertised feature I believe by vacaboca · · Score: 5, Informative

    Doesn't Comcast advertise this "SpeedBoost" as a feature - the language in their ads is something like "get massive super speed for the first 10MB of a download, then it will revert to your provisioned line speed"... So, it actually *is* a good thing rather than something to pad bandwidth tests, and it does generally help your general user, right?

    1. Re:This is an advertised feature I believe by andawyr · · Score: 5, Informative

      I agree - I know that Shaw Cable (Alberta) offers a plan that does exactly this: for 5-20 seconds, you get increased download bandwidth. This is their PowerBoost feature, that costs an extra $2.95 above your regular plan....

    2. Re:This is an advertised feature I believe by Ed+Avis · · Score: 5, Interesting

      So... how can you tweak your Bittorrent client to fool Comcast into thinking it is making lots of small downloads?

      --
      -- Ed Avis ed@membled.com
    3. Re:This is an advertised feature I believe by arivanov · · Score: 5, Insightful

      Torrents do that anyway. That is the reason why comcast have to beat them on the head. Each segment in the download is small enough to fit its "booster" criteria.

      Actually, there is nothing wrong with this approach. This means that interactive services and casual browsing are favoured vs bulk downloads. That is what every ISP wants to do anyway.

      --
      Baker's Law: Misery no longer loves company. Nowadays it insists on it
      http://www.sigsegv.cx/
    4. Re:This is an advertised feature I believe by ElizabethGreene · · Score: 5, Informative

      You are correct in your interpretation. The customer briefly receives more than they pay for after a period of inactivity, this throttles down to the 'purchased' bandwidth as the activity increases. For Read-Click-Load-Read web browsing this gets content in front of eyeballs quicker and is a "good" thing. If you are using a tiny file for a bandwidth test it screws up the results. HINT: USE A BIGGER FILE.

      People are out with pitchforks and torches over the "bad" thing Comcast does, throttling Torrent downloads, which works completely differently. To throttle a torrent, they forge a "I'm dead" packet from remote host, and send it to the customer. This causes the customer's torrent application to shop elsewhere for a feed. The repeated connect-forge disconnect-search-connect process slows the overall transfer. This only works because of the multi-peer technology underlying torrents, and wouldn't work with web browsing or ftp*.

      -Ellie
      * technically it would reduce the bandwidth usage, because it terminates the connection. This would result in broken connections and half-downloaded files. Then the pitchforks would REALLY come out.

    5. Re:This is an advertised feature I believe by croddy · · Score: 5, Funny

      Hey man, I use Linux -- this is one of my favorite computer games.

  2. Powerboost by SquierStrat · · Score: 5, Informative

    This is because of powerboost. As I understand it, powerboost makes the first 20MB download at a higher rate than your advertised bandwidth. Since bandwidth tests are done on such small files, you get a worthless result. The idea is that people who download lotsa of relatively small files get better performance, where as people downloading a lot of huge files like ISO images, full length movies, et cetera willg et initially good speed but after 20MB will feel like they are getting gipped.

    --
    Derek Greene
    1. Re:Powerboost by FritzTheCat1030 · · Score: 5, Informative

      I have Comcast's advertised 8 Mbps service and I very consistently get that downloading large files off of Usenet. I get about 25 Mbps for the first 20-30 seconds after I start a download.

  3. Web browsing optimisation by jackhererUK · · Score: 5, Informative

    Sounds like they have simply optimised their network to favour "bursty" usage, for example web browsing. This would seem a sensible thing for a consumer ISP to do.

  4. Token Bucket by Anonymous Coward · · Score: 5, Informative

    Um, this isn't a new concept, nor is it particularly sneaky:

    http://en.wikipedia.org/wiki/Token_bucket

  5. PowerBoost uses a 30 second average, not filesize by ben+there... · · Score: 5, Informative

    Torrents do that anyway. That is the reason why comcast have to beat them on the head. Each segment in the download is small enough to fit its "booster" criteria. No, that's not right.

    PowerBoost only accelerates the connection if the average speed you've been getting over the past 30 seconds* is less than the speed you are rated at/paid for. So if you have a 6 Mbps connection, that's 768 KB/s max. PowerBoost will raise that to up to 2 MB/s for a little less than 15 seconds, making your average for the past 30 seconds equal to 768 KB/s. After that, no matter how many new connections you open, your connection stays at 768 KB/s. But if your connection gets interrupted/throttled for a few seconds, you may get another boost after it resumes, until you are back to 768 KB/s 30 second average again.

    *it may be slightly more/less than a 30 second average. Boosts seem to last about 10-15 seconds, which would make sense with that number.
  6. Can't be right by ultranova · · Score: 5, Funny

    That can't be right. From your description, it sounds like a genuinely good and beneficial to the user idea. Where's the catch ?

    --

    Forget magic. Any technology distinguishable from divine power is insufficiently advanced.

    1. Re:Can't be right by Tassach · · Score: 5, Funny
      Any actually benefit to the customer is purely coincidental and unintentional.

      That nice warm shower feels pretty good until you realize someone is pissing on you.

      --
      Why is it that the proponents of "one nation under God" are so eager to get rid of "liberty and justice for all"?
  7. sheesh... by LordGlenn · · Score: 5, Informative

    http://www.dslreports.com/shownews/Slashdot-Keeps-Rediscovering-Comcast-Powerboost-91976