Comcast's Congestion Catch-22

An anonymous reader sends us to Telephony Online for a story about Comcast's second attempt at traffic management (free registration may be required). After the heavy criticism they received from customers and the FCC about their first system, they've adopted a more even-handed "protocol agnostic" approach. Nevertheless, they're once again under scrutiny from the FCC, this time for the way their system interacts with VOIP traffic. By ignoring specific protocols, the occasional bandwidth limits on high-usage customers interferes with those customers' VOIP, yet Comcast's own Digital Voice is unaffected. Quoting: "The shocking thing is just how big a Pandora's box the FCC has appeared to open — and it just keeps getting bigger. When the FCC first started addressing bandwidth usage and DPI issues, it quickly found itself up to its knees in network management minutia. Not long after that, it followed another logical path of the DPI question and asked service providers and Web companies about their use of DPI for behavioral targeting. Now it seemingly has opened up huge questions about what it means to be a voice carrier in the age of IP. It's not hard to imagine the next step: What about video? Telco IPTV services are delivered in roughly the same way as carrier VoIP services — via packets running on the same physical network but a prioritized logical signaling stream. Is that fair to over-the-top video service providers?"

Comments

Congestion?

[Mooga]

If Comcast is having major network congestion then why did they automatically double everyone's download speeds? I got a letter a few days ago saying that I now get 12 down rather then 6. Seems like a BAD idea if they are having congestion issues...

Re:Congestion?

[WhatAmIDoingHere]

Their issue is upload not download.

Re:Congestion?

[grumling]

You don't understand cable system design. The reason for the 6:1 ratio between upstream and downstream is not because Cisco (or anyone else) thinks you can oversubscribe the upstream spectrum, but because upstream carrier to noise ratios are much worse than downstream. Because of the lower CNR, upstream modulation has to have a lot more interleaving and error correction (and much lower symbol rates). It also helps isolate noise problems to a smaller service area.

Part of DOCSIS 3 spec is 64QAM upstream. Some operators are trying it now, and finding out that there's a whole new level of plant maintenance necessary to deliver a good upstream bit error rate. Meanwhile, the normal downstream carrier is 256QAM (6.4MSym/s symbol rate), which requires a 3dB improvement in CNR over 64QAM at the same symbol rate. As fiber is driven deeper into the cable network it will be much easier to increase the upstream modulation to 256QAM and downstream modulation at 1024QAM. Typical cable systems today use 16QAM modulation in the upstream, with a 3.2 MSym/s symbol rate.

And, it is fairly common to have multiple upstream carriers in a node (neighborhood). DOCSIS 3.0 adds support multiple downstream carriers* through devices called edge QAMS. The downside of that is most operators have 65 or so analog channels, several dozen digital cable channels, 4-5 VOD carriers, and one DOCSIS 2.0 carriers in the downstream. The push is to get rid of the analog channels, but that's politically unpopular since it would require all customers to get a set top box for every TV (someday tru-2-way TVs and set top boxes will be at Best Buy, but it's a long time coming). Once 3.0 is deployed, the typical system may have 3 or more bonded downstream carriers/service group, about 500 customers. End users will need a new modem to get full use of the channel bonding, but it should be worth it for the much greater increase in speed.

Finally, everyone always gets the "shared bandwidth" argument wrong. Most people think of DOCSIS like classic Ethernet, with a hub or daisy chain cable. This means that Ethernet NICs need to use CSMA/CA to avoid collisions. There is no way for a cable modem to hear another one, so the CMTS assigns a mini-slot to a cable modem when it is provisioned/registered (which essentially makes a TDMA channel). the ONLY time a modem is permitted to transmit is at it's assigned mini-slot. Over the years, CMTS software has improved, and operator's understanding of the configuration has become much more granular, to the point that bandwidth optimization is much better understood than it was 10 years ago, along with moving from 7200 series network engines to VXR and above (in the case of Cisco).

*There is some use of multiple downstreams now, it has been in the spec since DOCSIS 1.1, but isn't needed on much more than a temporary basis. Individual modems can only tune one carrier at at time, so it is typically used to get more customers on a node than it is used to get higher speeds. However, some operators have used multiple downstreams to isolate business class customers from everyone else.

Re:To pipe or not to pipe.

[Frosty Piss]

Why do ISPs insist on being more than just a pipe? It's so dumb no one wants them to be anything else. Do they just not feel useful when they are a pipe?

Because there isn't a lot of profit growth in being "just a pipe", and like all businesses, they would like to make more money.

Not a "Catch-22"

[Lord Byron II]

"Catch-22" implies a no-win situation. Comcast (and the other ISPs) have done this to themselves. They advertise unlimited Internet access (or make it seem like they're offering unlimited access) and then get upset when someone tries to use it.

The ISPs should start advertising their download speed, upload speed, and bandwidth caps openly. Offer additional speed and bandwidth for a reasonable price. And if your infrastructure is such that sometimes you'll need to throttle someone, make it clear upfront how and when such throttling will happen.

Right now, on Comcast's sale page, they only list the download speed of their connections. I couldn't find their upload speeds or the bandwidth caps (which I know to be 250GB). As far as I know, Comcast customers have no way to check to see if their being throttled or if they're near the bandwidth cap.

It's really no surprise then that customers are upset.

Not agnostic

[Ghworg]

If they are treating their own VOIP differently than other traffic then it isn't "protocol agnostic" at all.

Re:To pipe or not to pipe.

[Kugrian]

That's just great. ColdWetDog (752185) replying to Frosty Piss (770223). Mod me offtopic, but at least smile as you do it.

VOIP!=Internet

[not_anne]

"Comcast Digital Voice uses Internet Protocol and not the Internet. Comcast Digital
Voice calls travel on our private, managed network -- not over the public Internet. That makes
it superior to other 'Best Effort' services delivering phone traffic over the public Internet."

Source (emphasis mine): http://www.comcast.com/MediaLibrary/1/1/About/PressRoom/Documents/ProductsAndServices/digital_voice.pdf

You should know...

[AliasMarlowe]

Every other first world country has immensely higher population density.

Wrong, unless you're saying that Finland, Sweden, and Norway are not in the first world. http://en.wikipedia.org/wiki/List_of_countries_by_population_density

I live in Finland which has about 5 million persons at a population density of 15.6 per sq.km, while the US has about 300 million at 31 per sq.km, or double Finland's population density. Actually, about half of Finland's population is near the south coast (especially around Helsinki and Turku), while I'm in a rural area 300km north of Helsinki, so our regional population density is a bit lower. The largest town within 200km has about 80,000 people.

I have fiber to the house with 100/10 service available. The service is eur55 per month, including IP TV. If it's possible in the countryside in Finland, then it should be possible in most of US, where local populations and population densities are higher.

In fact, there are substantial areas of the U.S. with quite high population densities and local populations greater than all of Finland. Example: New Jersey, with 8 million persons at 438 per sq.km, and many millions more in adjacent areas. http://en.wikipedia.org/wiki/New_jersey

Your argument based on population density is a load of bollocks. You're just screwed by your ISPs.