February 13th, 2008
Comcast traffic management issue before FCC
Today is the deadline for the FCC call for comments on the Comcast traffic management case brought about by a formal complaint from the Free Press and Public Knowledge. As a former network engineer who designed networks and servers and as someone who has written extensively on these matters, I thought I would summarize the issues in a clear and concise manner.
Background
Independent groups last year found that Comcast was sending TCP RESET packets to BitTorrent seeders at various times of the day to cut back the number of upload sessions they could have. A BitTorrent seeder is someone who is not downloading but acting as a dedicated and peer-to-peer file server. BitTorrent downloads or uploads while downloading were not affected. Various groups complained that this was possibly illegal protocol discrimination using forged TCP RESET packets while Comcast maintained that this was reasonable network management to assure fair distribution of bandwidth to all their users.
The upstream contention problem
A typical Cable broadband network such as Comcast operates under the DOCSIS 1.1 standard which offers 10 mbps of upstream bandwidth and 40 Mbps of downstream bandwidth bandwidth shared amongst the neighborhood. Since the typical user has a static upstream cap of 384 kbps, it would be possible for 26 BitTorrent seeders and/or BitTorrent uploaders to completely jam the upstream pipe rendering the entire network unbearable. Since a typical Cable broadband company provisions between 50 and 400 users (typically somewhere in the middle) per cable loop, it is possible for ~10% of the users can jam the entire upstream network which ultimately affects downloads as well since services can’t be asked for. This is further complicated by the fact that DOCSIS networks use a reservation system for upstream traffic on a collision network. Too many requests for upload slots and the requests collide and no one gets to transmit anything.
Accusations of discrimination
Some have complained that this was content discrimination. But Comcast does not discriminate based on content; Comcast discriminates against excessive upstream usage that chokes up their entire broadband network. The EFF complains that this was “protocol discrimination” against BitTorrent and other P2P (peer-to-peer) applications, but it is a fact that BitTorrent and P2P are the biggest upstream bandwidth users. Since BitTorrent seeders who only continuously upload throughout the day can be reasonably classified as dedicated servers, they actually fall under prohibited services under Comcast’s TOS (Terms Of Service).
Blocking versus delaying
Comcast says they’re merely delaying BitTorrent seeders from uploading to their peers while their critics say they are blocking. It is true that Comcast blocks BitTorrent seeds when the broadband network is very busy, but they do allow BitTorrent seeding at most other times of the day. Network Engineer and Internet pioneer Richard Bennett explained this best in his comment to the FCC that since BitTorrent and other peer-to-peer applications all have the ability to resume transmission at where they left off, temporary blocking of seeders effectively acts as a delaying mechanism. The file eventually gets served to the remote party outside of Comcast’s network intact.
Consumer versus commercial Internet connection
The reality is that Comcast customers were never blocked, throttled, or delayed from receiving any services; they were delayed from offering hosting services (BitTorrent seeding) that were technically prohibited to begin with under the terms of service. Comcast’s consumer broadband service technically doesn’t have to act as a commercial hosting service to other customers in and outside of Comcast’s network so the fact that they permit seeding most of the day seems like a reasonable compromise. Furthermore, BitTorrent users who are downloading are continuously uploading during the download without any delaying action so it isn’t as if Comcast refuses to participate in P2P uploads.
Blocking of Lotus Notes
Comcast’s network management mechanisms did have a bug in them that accidentally blocked Lotus Notes traffic, but this issue was fixed months ago when the issue was first brought to the attention of Comcast. All software and hardware implementations have bugs and we expect the service provider to act in good faith and repair the problems as soon as possible. In this particular case, Comcast appears to have acted quickly and properly by fixing the problems that blocked Lotus Notes.
The complaint to the FCC
The Free Press and Public Knowledge filed a formal complaint to the FCC to immediately enjoin Comcast from these network management practices before the merits are decided and the facts weighed. This is an unreasonable request since Comcast customers would be harmed by network traffic jams due to the lack of any traffic management. The Free Press and Public Knowledge also demanded fines of $195,000 per infraction which would amount to over $2 trillion dollars if we counted every Comcast customer. This is obviously impossible since it exceeds the gross revenue of any corporation in the USA.
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George Ou is Technical Director of ZDNet. See his full profile and disclosure of his industry affiliations.
