Ordered by the FCC to cease blocking P2P protocols, Comcast has revealed how they plan to comply in a "protocol-agnostic" manner. This has been a fascinating look at the inner workings of a large ISP, but can we trust them to treat heavy Internet users fairly?
In “We’re Not Blocking Traffic" – How Comcast Did It, we looked at the nuts and bolts (actual hardware and policy) that allowed Comcast to interfere with peer-to-peer networking. They did this by watching upload traffic and sending “RST" or reset messages to computers using bandwidth over a certain threshold. Specifically, this was targeted at BitTorrent, Gnutella, Fastrack, and other P2P protocols. This garnered the ire of the FCC who subsequently made “net neutrality" an official US policy by ordering Comcast to cease interfering with any specific type of traffic.
The Network Now
On Friday evening, September 19, 2008, Comcast answered the FCC. Included were attachments that described their current management practices and their proposed “protocol-agnostic" future management practices. (See Comcast Link below)
As a brief review, let’s look at how Comcast’s High Speed Internet network works. Cable runs from the cable modem in a customer’s house, which joins with the cables from neighbors' houses, where it links to a Cable Modem Termination System (CMTS). There, the link becomes digital fiber. Comcast currently uses a device called the Sandvine PTS 1810 to monitor and shape network traffic, and it is placed near the CMTS.
The Future Network
Continuing to take a nuts and bolts approach, let’s look at what hardware and policies Comcast plans to use in the future to comply with the FCC’s directive.
First of all, Comcast is installing new hardware. Trials of the new system are already underway in Pennsylvania, Florida, Colorado, and Virginia. The hardware consists of three types of servers that are mounted remotely near Regional Network Routers (RNRs) which are upstream from the CMTS. These new servers are called Internet Protocol Detail Record (IPDR), Congestion Management, and PacketCable Multimedia (PCMM) servers.
Implementing the protocol-agnostic management policy requires a change in the firmware of the customers’ modems. The firmware in a modem keeps up with things like the user’s account name and provisioned bandwidth (maximum download and upload speeds). Cable modems are often “flashed" to update their firmware based on the changing needs or capabilities of the network.
The modem update introduces two new operating modes. These are called PBE, for “Priority Best Effort", and BE, for “Best Effort," traffic.
BE is the normal mode for all modems on the High Speed Network, except when:
- The usage level upstream or downstream measured over a period of time nears the point where congestion could degrade other users’ Internet experience.
- The particular subscriber is making a “significant contribution" to the bandwidth usage at the particular port over the same period of time.
Congestion State and Consumption State
Once a particular port is in what Comcast calls a “Near Congestion State," the software on the upstream servers checks to see if the user has entered an “Extended High Consumption State." If so, the cable modem is told to switch to the slower BE mode.
What activates BE is an extended 70% or more utilization of the provisioned bandwidth during a 15-minute period. When this happens, BE basically marks the user’s traffic as having lower priority than other non-high consumption users.
Although not stated, Comcast is still concerned about those P2P users causing congestion, particularly on the upload side of the asymmetric equation (where more download bandwidth is provisioned than upload bandwidth). These are the users most likely to be affected by Comcast’s new network management practices.
How Will it Affect Users?
How bad will it get for high bandwidth users? (Some could call them “bandwidth hogs" and some could say that they just want to receive what they pay for.)
Comcast says there could be choppiness in VOIP communication, sluggish page load times, and slowed P2P uploads. They point out that the same thing can happen in the absence of any active network management.
How many users might this affect? Comcast found, “. . . in Colorado Springs, CO, the largest test market, on any given day in August 2008, an average of 22 users out of 6,016 total subscribers in the trial had their traffic priority status changed to BE at some point during the day."
Comcast’s network management policies will continue to evolve as they get more experience with their protocol-agnostic techniques. An important indication that the techniques are working is that: “To date, Comcast has yet to receive a single customer complaint in any of the trial markets that can be traced to the new congestion management practices, despite having broadly publicized its trials."
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