Comcast Details Net Management Moves

MSO supplies FCC with details about Comcast's new network management system and a plan to install it everywhere by year's end

Jeff Baumgartner, Senior Editor

September 22, 2008

8 Min Read
Comcast Details Net Management Moves

Comcast Corp. (Nasdaq: CMCSA, CMCSK) submitted a series of filings with the Federal Communications Commission (FCC) last Friday that describe the MSO's new "protocol agnostic" network management platform it intends to migrate to by year's end, as well as additional info about the existing system that plunged the MSO into hot water in the first place.

Comcast filed the documents after the FCC published an order on Sept. 20 that calls on the operator to stop throttling peer-to-peer (P2P) traffic and halt its "discriminatory network management practices." The FCC gave Comcast 30 days to disclose its current practices, provide a compliance plan on how it will stop those practices by the end of the year, and give greater detail about the network management system that will replace the one that's in place now. (See FCC Puts Comcast on the Clock .)

Comcast is asking the Court of Appeals for the D.C. Circuit to reverse the order, but, nonetheless, has agreed to comply with the FCC's request for information. (See Comcast Strikes Back .)

Deployment benchmarks
In addition to a previously announced commitment to transition its entire broadband network to a "protocol agnostic" network management system by the end of the year, Comcast also outlined several other "benchmarks" it expects to meet before then.

Among them, the MSO said it will have completed the installation of PacketCable Multimedia (PCMM) and Internet Protocol Detail Record (IPDR) servers by Oct. 15. By then, it will have also have begun to install "Congestion Management Fairshare" servers from Sandvine Inc. . (See Sandvine Unveils FairShare and Comcast Deploys Sandvine.) [Ed note: More details about these network elements follow further down.]

By Nov. 15, Comcast will have begun commercial "cutovers" to the new system on a market-by-market basis. Once the network-side gear is in place, Comcast will then install software updates on customer cable modems in those given areas and disable the company's current congestion management system.

Comcast said it will send emails to customers at least two weeks before the new system is commercially deployed in a given market. Comcast did not say where the cutovers will occur first, but the MSO is already conducting technical trials of the new system in Chambersburg, Pa.; Warrenton, Va.; Lake City and East Orange, Fla.; and Colorado Springs, Colo. (See Comcast Ready to Test New Traffic Cop.)

Comcast indicated it expects to report to the FCC by Jan. 5, 2009, that it has discontinued its "protocol-specific" congestion management practices across the board in favor of the new platform.

The new system
In a separate filing, Comcast detailed the "protocol agnostic" system that's set to replace the existing one, which singles out how some upstream P2P traffic is managed and delayed. (See Comcast Defends P2P Management .) And it sounds pretty much like the MSO has previously described it -- that some customers could be slowed down temporarily if they are gobbling up an exorbitant amount of capacity, regardless of what type of application they may be using. (See Comcast CTO: Manage People, Not Protocols.)

In the first step, new network software will continuously monitor aggregate traffic usage data for individual segments on the MSO's high-speed Internet network. If overall upstream or downstream usage on a particular segment breaches a predetermined level, the software then determines which customers are using a "disproportionate share of the bandwidth." If the software further discovers that certain subscribers are the source of high volumes of network traffic during a given "period of minutes," traffic for those customers "temporarily will be assigned a lower priority status."

Comcast had earlier confirmed that customers who are subject to this policy could experience slower speeds in the range of 10 to 20 minutes, or until the state of congestion clears up. But that's just a rough guide. (See Sandvine: We're Fine .) However, traffic won't be delayed at all if the system ultimately determines that the particular network segment is not experiencing congestion.

Next Page: Piecing it together

Piecing it together
As for implementation, Comcast will purchase new hardware and software that will be deployed near the MSO's Region Network Routers (RNRs). Those elements include the IPDR servers, which collect relevant cable modem volume usage information from cable modem termination systems (CMTSs), Congestion Management Fairshare servers from Sandvine, and PacketCable Multimedia (PCMM) servers from Camiant Inc.

Sandvine's piece of the puzzle will use Simple Network Management Protocol (SNMP) to detect when CMTS ports are close to reaching a state of congestion. If any users need to be managed, the Sandvine server will relay that information to the Camiant PCMM server, which, in turn, will signal the CMTS to apply the proper traffic prioritization policy. (See Camiant Intros 'Fair Use' Bandwidth System.)

Comcast has not picked a vendor for the IPDR component, but said it's in "active negotiations" with several.

Coupled with that network-side work, Comcast will also send new "bootfiles" to customer cable modems that will result in the creation of two quality of service (QOS) levels: one for "Priority Best-Effort" (PBE) traffic, and another for "Best Effort" (BE) traffic.

From that point on, all traffic going to or from the modem will be designated either PBE or BE. While PBE is the default setting, BE will be invoked if two conditions are met:

  1. The usage level of a particular upstream or downstream port of a CMTS, over a given span, is nearing the point where congestion could degrade the experience of other customers. Based on trials to date, Comcast said a typical CMTS port on its high-speed Internet network will be in this "Near Congestion State only for relatively small portions of the day."

  2. And, a particular subscriber is found to be making "a significant contribution to the bandwidth usage on the particular port" over a given period of time. Under this "Extended High Consumption State," a customer must consume greater than a certain percentage of his or her "provisioned upstream or downstream bandwidth" (a tier that caps usage at 8 Mbit/s downstream by 1 Mbit/s upstream, for example) over a specific length of time. Based on a range of tests and evaluations, Comcast has determined that the appropriate starting point for the "User Consumption Threshold" is 70 percent of a subscriber's provisioned upstream or downstream bandwidth. The starting point for the "User Consumption Duration" is 15 minutes.

Any delay resulting from network congestion will affect BE traffic before it affects PBE traffic, Comcast said.

Based on data culled from the markets where Comcast is already testing the protocol agnostic system, less than one third of 1 percent of subs had their traffic priority status changed to the BE state on any given day. In Colorado Springs, the largest market in the early test pool, 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, according to the MSO.

"In trials, we have observed that user traffic rarely remains in a managed state longer than the initial 15-minute period," Comcast noted, adding later that it has yet to receive a single customer complaint in any of those trial markets that can be traced to the new congestion management system.

More on PBE and BE
But what's the difference between PBE and BE? Comcast has stated previously that customers who are subject to any delays can still expect to get a "really good DSL experience" until congestion clears up again.

In the filing last week, Comcast explained that a certain number of packets can be processed by the scheduler in any given moment. For each time slot, PBE traffic gets priority access to the available capacity, and BE traffic is processed on a space-available basis.

Comcast used a bus stop analogy to further explain how BE packets are treated during a period of congestion. Empty buses arrive at a figurative "bus stop" every two milliseconds, and each bus fills up with as many packets as it can hold based on the number of seats it has available. During non-congested periods, the bus will typically have several empty seats, but, during congested periods, the bus will fill up and some packets (those assigned BE status) will have to wait for the next bus.

It's during these congested period that BE packets will be affected. If there's no congestion, packets from a customer in a BE state should be able to jump on the bus when it arrives. But if there is congestion, PBE packets will get priority over the BE packets.

"In that situation, the BE packets would have to wait for the next bus that is not filled by PBE packets. In reality, this all takes place in two millisecond increments, so even if the packets miss 50 'busses,' the delay only will be about one tenth of a second," Comcast stressed. "Depending upon the level of congestion in the CMTS port, this [BE] designation may or may not result in the user's traffic being delayed, or in extreme cases, dropped before PBE traffic is dropped."

But stay tuned
Comcast noted multiple times that it may "refine the details of our new practices" and, if so, will detail them in further filings in the FCC docket. Comcast also held that these new network management policies are "independent of" its decision to apply a monthly data usage threshold of 250 gigabytes per account for all residential cable modem subscribers. (See Comcast Draws the Line at 250GB.)

— Jeff Baumgartner, Site Editor, Cable Digital News

About the Author(s)

Jeff Baumgartner

Senior Editor, Light Reading

Jeff Baumgartner is a Senior Editor for Light Reading and is responsible for the day-to-day news coverage and analysis of the cable and video sectors. Follow him on X and LinkedIn.

Baumgartner also served as Site Editor for Light Reading Cable from 2007-2013. In between his two stints at Light Reading, he led tech coverage for Multichannel News and was a regular contributor to Broadcasting + Cable. Baumgartner was named to the 2018 class of the Cable TV Pioneers.

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