Original URL: http://www.theregister.co.uk/2008/03/31/richard_bennett_comcast_bittorrent_detente/

Everyone's a winner in the Comcast - BitTorrent detente

Everyone except the Neutralists?

By Richard Bennett

Posted in Broadband, 31st March 2008 18:59 GMT

Analysis So Comcast will stop shaping peer-to-peer seeding sessions with spoofed TCP RST commands. I caught up with the cable giant's CTO Tony Werner on Thursday for more details.

The move should delight the company's critics. These innocent control packets have been compared to identity theft, to collusion with dictatorial regimes, and outright hacking of customer systems. BitTorrent may not be an IETF-sanctioned RFC protocol in its own right, but Comcast has decided to bind itself to traffic management practices that don't produce obviously non-standard packets. Instead, they're going to install additional equipment that will do real-time traffic accounting by user, feeding back information to the cable infrastructure that will equitably distribute opportunities to offer upstream traffic. In essence, this system makes the cable standard DOCSIS much more sophisticated; now it will behave just like DSL, only faster.

In DSL systems, each customer typically has a dedicated physical cable to a DSLAM, a type of concentrator. The DSLAM aggregates customer data onto a common upstream link according to a fairness algorithm that picks frames for from buffers at the heads of these dedicated links in a manner that minimizes bandwidth hogging. In the new Comcast system, the fairness algorithm is deployed in the CMTS (the cable equivalent of a DSLAM), and acts on buffers in each customer's cable modem. The CMTS is able to do this because DOCSIS data transfers from customer to network are preceded with brief requests for bandwidth. Armed with intelligence about each user's recent traffic history and the state of the network generally, the newly-intelligent CMTS will schedule bandwidth by customer according to a fairness algorithm of its own, with the same range of choices that exist for DSLAMs.

All's Fair That is Fair?

Under the new regime, Peer-to-Peer seeding will be treated neither better or worse than any other use of upstream bandwidth, unless it imposes a greater load than the typical customer, and then only when the network as a whole is heavily burdened. When the network is lightly loaded, management will presumably be lighter than it has been, because the hard caps in today's cable modems won't be necessary.

Combining this traffic management system with the enhancements Comcast has already announced for its network in areas where they butt heads with Verizon FiOS and AT&T's U-verse , giving its customers shared 130 Mb/s downstream and 100 Mb/s upstream. In terms of performance, that parks Comcast in the space between two telcos. Verizon's fiber-to-the-home and lightly loaded concentrators will continue to provide it with max headroom for moving traffic as fast as customer equipment permits [disclosure: I currently work for the company that sells customer-premises routers to Verizon], but Comcast will be able to outperform AT&T fiber-to-the-curb network in most scenarios.

The significant fact for network neutrality champions is simply this: Comcast will no longer care about the content of your packets, only their number. You'll always get a fair share of the pie, whether that's a lot (as it usually will be) or a little, and the pie's getting bigger.

Shooting the Lobbyist's Fox

So the news prompted praise from our self-appointed guardians of net neutrality, er … right?

Sadly, no. The surprise announcement of the deténte was apparently so stunning it left many at a loss for words.

Free Press, co-petitioner with BitTorrent competitor Vuze in demanding harsh fines and immediate injunctions against Comcast, was silent most of the day, only going public to proclaim the deal meaningless after press deadlines. But Free Press' lamentation was mild compared to the reaction of file sharing enthusiast Robb Topolski, who characterized it as "treachery".

FCC petitioner Public Knowledge sniffed that the agreement was simply "irrelevant", and the Media Access Project still hasn't commented publicly, not even on their Sr. VP Harold Feld's popular blog.

Make Memoranda, not War

But the deal is neither a betrayal nor a non-event, and it shouldn't have been a surprise. Networking depends on co-operation at every level, and technical solutions have always been more highly prized by the networking industry than the broad and unworkable government mandates that the interest groups have been seeking.

Note that the people who run BitTorrent, Inc itself understand this well enough: they conspicuously didn't petition the FCC to fine Comcast in the first place. And the people who run Comcast appreciate that a Memorandum of Understanding with a business-minded BitTorrent is preferable to a Consent Decree with a politically driven FCC.

Policy created in election years tends to be infused with hyper-polarization, so to the extent that Comcast and BitTorrent can make the FCC calm down and let business take its course, consumers will be the winners. For the moment, BitTorrent also has a leg up on its litigious competitor in peer-to-peer TV, Vuze. But these two rivals may reach parity if the latter decides to focus on its core business, rather than than lawsuits that enable Vuze to profit from the use of other people's software to distribute other people's content over (still) other people's bandwidth.

A smarter network beats the dumber network

Another winner in the new Comcast order is tradition.

Since the days of three-digit RFCs, it's been standard practice for network operators to correct the TCP protocol's mistaken notion that fairness consists of the right to consume bandwidth in proportion to ones appetite by applying fair queuing at the entry to the first hop. One of the first to write about this was John Nagle, father of "Nagle's Algorithm", and the key internet RFCs 896 and 970.

Writing on Slashdot, Nagle said recently:

The way [congestion control] was supposed to work is that TCP needs to be well-behaved because it is to the advantage of the endpoint to be well-behaved. What makes this work is enforcement of fair queuing at the first router entering the network. Fair queuing balances load by IP address, not TCP connection, and 'weighted fair queueing [sic]' allows quality of service controls to be imposed at the entry router. "

The losers are those who still think, against all the evidence, that the Internet is a "stupid network".

New equipment permits Comcast to enforce fair queuing at the first router inside their network, and a better understanding of tradition motivates BitTorrent to curb its appetite. In the future, this equipment and its complements will permit users to apply their own preferences to the various streams they generate at the same time, so they won't even have to worry about the effect that one member of their family's uploads have on others' web browsing and VoIP sessions.

Comcast isn't there yet, but the replacement of application-centric network infrastructure with traffic-sensitive equipment is a strong step in the right direction, and all of us who buy network services from the cable company should be happy about it.®