Tim Lee

Skype as a Bandwidth Hog?

Ars has an interesting story about three California colleges that have decided to ban Skype from its campus. The school administrators have what strikes me as a puzzling attitude toward the service, describing it as a “potentially illegal waste of resources,” without explaining what might be illegal about it. Perhaps they’ve somehow gotten the erroneous impression that there’s something inherently illicit about “grid-computing-like” network applications.

Aside from legal concerns, the other issue seems to be bandwidth:

according to the Office of Information Technology, the chief problem comes when a Skype client acts as a “supernode” and makes itself available to relay calls made by other users. Having numerous supernodes on a school network increases bandwidth consumption and has a detrimental impact on connectivity, according to the memo. Anecdotal reports from individual Skype users reveal that bandwidth consumption can increase by as much as an entire gigabyte per month for a single Skype client when it acts as a supernode.

If my math is right, 1 gigabyte per month is roughly 3 kilobits per second, a trivial amount of bandwidth on a modern campus network. Even if the bandwidth is concentrated in shorter bursts–say, if the whole gigabyte is transmitted in a single hour–that’s still a rate of only 2.2 megabits per second–roughly the bandwidth of a typical DSL line. This is not a particularly abusive use of the network.

September 25, 2006 | Comments |

Viewing 10 Comments

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    I think the key claim (via Paul Kedrosky) is that Skype users within the university are giving away university bandwidth to outsiders, which is against the university's Terms of Service.

    But- and this is an honest, serious question- why is this troubling? Isn't this kind of monitoring and traffic shaping exactly the kind of thing that poo-pooers of net neutrality say is perfectly legitimate for pipe-owners to do?
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    Or to put the question as a hypo: if, say, AT&T; had banned Skype on their network, the net neutrality crowd would be up in arms, and this blog would (I presume) support fully AT&T;'s right to do it. So why is this variant of the hypo bothersome to you, Tim?
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    I support the University's right to administer their network as they please. That doesn't preclude me from criticizing them when they make decisions I think are stupid.
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    Fair. You do realize that the pressure to economize on scarce-ish bandwidth will lead to a lot of stupid decisions, right? :)
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    Well, to turn this around, do you think there should be a federal rule prohibiting universities from prioritizing the use of the bandwidth they provide to their students and faculties? When I was at the University of Minnesota, I shared an office with a guy on the campus network security staff, and he spent a lot of his time figuring out ways to rate-limit peer-to-peer applications. This wasn't because they particularly cared about piracy--they were just spending thousands of dollars a month on high-speed Internet access, and wanted to make sure that bandwidth was available for research purposes. That strikes me as a legitimate goal in general, even if in this case they seem to be singling out Skype for unfair attention given that the application's bandwidth use is typically quite modest.

    The vast majority of universities still permit Skype, and hopefully criticism from their students and faculties (and a little lobbying from eBay) will get these universities to change their mind. I'd rather have a thousand different network administrators making these kinds of decisions for their own campuses than have a federally-determined "bandwidth hog" list that determines which applications may be rate-limited by universities.
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    Skype (at least as of 2.0.0.105) does not provide any means to gate, limit or shape bandwidth at the client. It appears to use the latent connections you have with other Skype clients to determine how much bandwidth you have available and whether or not you can become a supernode.

    When running on a large campus network, it is possible for a p2p client to be mislead into believing you have greater bandwidth potential, because your campus backbone may be very fast , while individual uplinks to the greater network may be slower.

    So while individually a client may only use a small bit rate, when aggregated across many possible clients on a campus you could potentially swamp the campus uplinks to the Internet (say 500 clients each handling 96kbs, resulting in a potential 48Mbs of bandwidth in use).

    I've had to turn off Skype whenever I'm on wifi or gprs, not because it doesn't work (call quality is typically fine), but because it works too well and starts routing other calls through my system, consuming the limited bandwidth I have.
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    The post office regulates the size and weight of packages without regulating the content of packages*; we don't consider the regulations on size and weight to be speech burdens. Similarly, I'd suggest that it should be possible (though I admit I haven't thought the details through in great detail) to construct common carrier rules which allow bandwidth providers to moderate the volume of bandwidth used without passing judgment on the legality of the programs using the bandwidth or the speech contained in the bandwidth.

    * there are of course exceptions to this, but they don't really impact the analogy.
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