Slowed, Not Stopped

By Larry Seltzer  |  Posted 2008-09-25 Print this article Print

After a conversion being performed on cable modems now, Comcast will use two QoS performance levels for traffic. The default is PBE (Priority Best-Effort) and there is a lesser BE (Best-Effort). If a user is identified as being above their user consumption threshold while their port is at a near consumption state, that user's traffic will shift from PBE to BE. It won't be stopped, it will be slowed down, and therefore consume less of the overall bandwidth on that port. The user will be returned to PBE state when their consumption moves below 50 percent utilization for approximately 15 minutes.

How bad can BE be? The CMTS has a scheduler, and PBE traffic gets (you guessed it) priority. BE traffic gets processed on a "space-available" basis. It's probably not a huge difference, even at a busy time, but a heavy user will notice the difference. Comcast says they tested for the worst-case scenario, that a CMTS is 100 percent utilized and BE traffic is completely stalled, but it just didn't happen. They claim that they have never received a complaint in their test markets for these techniques from a user that can be traced to the new management practices.

Not long ago Comcast also announced that they would be limiting monthly residential data usage to 250GB. This is not part of the same policy, although in a way it's the same thing, but with a longer time window, and the limit is hard rather than a throttled limit. I think of the 250GB limit a different form of capacity management. (Incidentally, this works out to about 100K bytes/second all month.)

I've never gotten all that excited about net neutrality. It all seems kind of paranoid to me. But if you really are worried about major telecom providers treating applications and protocols and services in a discriminatory fashion then I don't think you can have a problem with Comcast's plan, at least as they have described it here. You can't deny them the capability to manage their network so that capacity is maintained for all users.

Some will complain that users are being punished for using the service to its advertised capacity, and there's some rhetorical truth to that. But cable modem has more of a shared bandwidth component than other broadband offerings and it's just plain common sense that you can't hog it. And the few people who are abusive are the ones who know better. If you absolutely must have huge amounts of bandwidth at all times, go buy yourself a dedicated line. Oh, you don't want to spend all that money? Guess it wasn't all that important to begin with.

Security Center Editor Larry Seltzer has worked in and written about the computer industry since 1983.

For insights on security coverage around the Web, take a look at Security Center Editor Larry Seltzer's blog Cheap Hack.

Larry Seltzer has been writing software for and English about computers ever since—,much to his own amazement—,he graduated from the University of Pennsylvania in 1983.

He was one of the authors of NPL and NPL-R, fourth-generation languages for microcomputers by the now-defunct DeskTop Software Corporation. (Larry is sad to find absolutely no hits on any of these +products on Google.) His work at Desktop Software included programming the UCSD p-System, a virtual machine-based operating system with portable binaries that pre-dated Java by more than 10 years.

For several years, he wrote corporate software for Mathematica Policy Research (they're still in business!) and Chase Econometrics (not so lucky) before being forcibly thrown into the consulting market. He bummed around the Philadelphia consulting and contract-programming scenes for a year or two before taking a job at NSTL (National Software Testing Labs) developing product tests and managing contract testing for the computer industry, governments and publication.

In 1991 Larry moved to Massachusetts to become Technical Director of PC Week Labs (now eWeek Labs). He moved within Ziff Davis to New York in 1994 to run testing at Windows Sources. In 1995, he became Technical Director for Internet product testing at PC Magazine and stayed there till 1998.

Since then, he has been writing for numerous other publications, including Fortune Small Business, Windows 2000 Magazine (now Windows and .NET Magazine), ZDNet and Sam Whitmore's Media Survey.

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