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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?"

27 of 177 comments (clear)

  1. Congestion? by Mooga · · Score: 5, Insightful

    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...

    --
    ~ Mooga
    1. Re:Congestion? by WhatAmIDoingHere · · Score: 5, Interesting

      Their issue is upload not download.

      --
      Not a Twitter sockpuppet... but I wish I was.
    2. Re:Congestion? by timeOday · · Score: 4, Insightful

      Yeah because they buy non symmetrical DS3's and above amirite?

      I doubt the problem is up at that level anyways. The price per byte on the backbone is so cheap it hardly matters. It's the few miles nearest end users - where most of the network actually is - that matters.

      I wish they (all ISPs) would start honoring TOS flags and then start selling packages like X gigabytes of 1st class traffice, Y gigabytes of 2nd class traffic, and Z gigabytes of 3rd class traffic. Presumably people would use 1st for VOIP, 2nd for ssh or websurfing, and 3rd for bittorrent. But if somebody configures bittorrent to use 1st class, it's not the ISPs problem.

      All that said, I have comcast's very slowest "broadband" - 768kbps (i.e. under 1 mbit), and vonage always works fine. I haven't noticed any congestion problems on their network.

      Finally, why the submitter thinks video is such a dilemma is a bit of a mystery to me. 99.9% of video is download - not interactive video phones and such - so having some jitter isn't really a problem, easily solved with buffering. It doesn't need to compete on the millisecond scale with voice traffic.

    3. Re:Congestion? by drinkypoo · · Score: 4, Informative

      The problem is that the DOCSIS spec involves having your own little slice of frequency for downstream but everyone shares upstream. Your DOCSIS 1 stuff would let you dump 5 or 6 megabits to each of thousands (well, okay, maybe hundreds) :) of subscribers at once if you could actually feed the data into your head end fast enough. But sending the data back upstream is done on a shared frequency. Some line cards have multiple frequencies (no idea what they are now; when I worked for Cisco Santa Cruz when they were developing the Cisco DOCSIS modem ref design firmware it was the MC11 and MC16, I think, the MC16 had six upstream channels) so that you could send the same downstream to a whole bunch of places, but segment their upstream and feed it into the different upstreams (inputs on the line card.) If you run out of bandwidth you can charge more, and buy more bandwidth. But if you run out of upstream bandwidth on the line card, you have to add a line card and go forth and physically segment your network.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
    4. Re:Congestion? by Sancho · · Score: 4, Insightful

      Is that why they instituted download caps?

    5. Re:Congestion? by SanityInAnarchy · · Score: 3, Insightful

      start selling packages like X gigabytes of 1st class traffice, Y gigabytes of 2nd class traffic, and Z gigabytes of 3rd class traffic.

      That seems like it would be a bit complex, and also problematic if they did not ship their own routers and instructions for configuring it.

      Why not just sell pure bandwidth, and if people want to prioritize things, let them do it within their own networks? If I'm saturating my connection with BitTorrent, it's really up to me to QoS it down until Skype works. But, if I'm saturating my connection with BitTorrent, and someone else is having problems with Skype, that suggests they should buy more bandwidth.

      I can see where TOS might be easier for the ISPs, let them squeeze a bit more out of their networks, maybe oversell a bit more and acknowledge that your torrent will slow to a crawl (but your voice will still work) during "peak" hours.

      On the other hand, Amazon seems to be able to put a relatively cheap, relatively constant price on all network traffic to Amazon Web Services. I don't know if my bill is typical, but I pay $65 for fiber -- split evenly, that would be 300 gigs upload and 176 gigs download, or 150 gigs up and 265 gigs down... per month. I mean, I might do more than that torrenting, but not much, and I imagine that's a good deal more than Comcast currently provides.

      --
      Don't thank God, thank a doctor!
    6. Re:Congestion? by HangingChad · · Score: 4, Funny

      I doubt the problem is up at that level anyways.

      It's probably the NSA's traffic cloning and storage system that can't keep up with trying to record all of America's VOIP calls. We're sorry, but this mailbox...United States of America...is full.

      --
      That's our life, the big wheel of shit. - The Fat Man, Blue Tango Salvage
    7. Re:Congestion? by grumling · · Score: 5, Informative

      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.

      --
      "Well, good luck finding a judge that doesn't run a bestiality site."
    8. Re:Congestion? by jo42 · · Score: 3, Informative

      The problem is that ISP's pay per megabyte for uploads. Downloads are free for them except for the cost of the line and equipment maintenance., etc.

      Horse crap. ISPs pay the same for bandwidth usage up or down.

  2. Second Post... by paintballer1087 · · Score: 4, Funny

    It would have been first, but someone was on the phone.

  3. How much is self intereference? by nweaver · · Score: 4, Interesting

    If someone is doing very high traffic, enough to get into Comcast's temporary "QOS Low" category, they are probably sending and full rate. If you are sending at full rate, the typical end-host NAT and buffering alone will cause bad quality for VoIP (search for VoIP and BitTorrent for a lot of such tales). There is nothing Comcast's network management really does to affect things in this case anyway.

    Comcast's network management should only cause additional VoIP issues when the big transfer STOPS and the VoIP call is made within only a few minutes (before the user's link is reclassed back into the "QoS normal" category).

    --
    Test your net with Netalyzr
    1. Re:How much is self intereference? by Sancho · · Score: 4, Insightful

      Did you read the part in the summary which said that Comcast VOIP was unaffected by this problem?

    2. Re:How much is self intereference? by Jah-Wren+Ryel · · Score: 4, Informative

      Did you read the part in the summary which said that Comcast VOIP was unaffected by this problem?

      What was not mentioned is that Comcast's VOIP is out of band. I'm no comcast apologist (comcast's policies were the straw that broke the came'ls back and got me to move to a new house where I could get verizon FIOS) but this is less of an issue that it has been made out to be. From day one, comcast's VOIP has used seperate channels from their internet services. Their VOIP is limited to connecting to POTS or other comcast VOIP customers. It is not on the internet, it is only on a comcast private intranet.

      --
      When information is power, privacy is freedom.
    3. Re:How much is self intereference? by isdnip · · Score: 4, Informative

      To clarify... Comcast Digital Voice, like any PacketCable service, uses reserved capacity. It comes off of the cable modem channel, at the physical layer (minislots), and it keeps the telephone calls off of the Internet. CDV is NOT an Internet phone service at all. It's a separate access network, using MGCP-derived signaling and RTP/IP encapsulation of voice.

      If the phone is not in use, then a tiny bit more capacity on the cable (100 kbps/call) is made available for data. If you think that's unfair, fine, but that's how PacketCable works, and it maximizes efficiency for the whole system. It's safe, legal, and non-fattening.

  4. To pipe or not to pipe. by Dyinobal · · Score: 3, Interesting

    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?

    1. Re:To pipe or not to pipe. by Frosty+Piss · · Score: 5, Insightful

      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.

      --
      If you want news from today, you have to come back tomorrow.
    2. Re:To pipe or not to pipe. by ChromaticDragon · · Score: 4, Insightful

      Sadly with regards to Comcast, it's because they don't consider themselves primarily an ISP.

      It's not that they are an ISP and they want to be something else. It's that they are "SOMETHING ELSE" and DOCSIS came around and they looked and said "Hey. While we're at it we could charge folk a few extra bucks a month and give them Internet too." So it's very easy to understand how they wish to ensure you use THEM for your VoIP and video-on-demand needs.

      Seriously. Call their help line. Listen to their canned message while you're on hold. Does it say anything remotely close to "we want to be your ISP"? Nope. It says something like "we're happy to be your ENTERTAINMENT company".

      Nothing really surprises me anymore about their horribly pathetic reliability once you realize their idea of what they are.

    3. Re:To pipe or not to pipe. by Kugrian · · Score: 5, Funny

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

  5. 911 by WindowlessView · · Score: 4, Funny

    If you have VOIP, don't set your kitchen on fire during high congestion periods. Please people, a little take a little personal responsibility.

    --
    Leave the gun, take the cannolis.
  6. I don't know by MindStalker · · Score: 4, Insightful

    Why don't they just UPGRADE THE PIPES.
    My god every other first world country has huge bandwidth where these types of things aren't even a consideration. Yet comcast just whines because you can't run everything and be fair on tiny pipes.

    1. Re:I don't know by drinkypoo · · Score: 4, Informative

      My god every other first world country has huge bandwidth where these types of things aren't even a consideration.

      Every other first world country has immensely higher population density. Canada's population is overwhelmingly located in certain centers and the remote population of Canada has just as much trouble as the remote population of the USA.

      This does not adequately explain why we don't have higher speed in the areas of extremely high population density, of course.

      We can solve these problems by forming community ISPs to wirelessly handle the last mile solution, which works in most places. Using solar-powered (or hell, wind-powered, it's very easy) mesh networks would work practically everywhere. IMO we would ideally replace the internet entirely with an alt-power mesh network. You can cross hills by putting a wind generator on top, running PoE as far as possible and putting PoE APs at each end of the wire. Wind generators can be made entirely out of junkyard parts (as can a welder to build it with, if you are crafty. a plastic fuel tank, some jumper cables, some scavenged wire and you've got a welder. The wind generator itself is made out of body metal, a steering knuckle, a wheel, an alternator. Easier to make with an oil drum instead of the body metal, though.

      The problem here is one of "meh". We have great ideas but never seem to execute. I put myself in this category.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
  7. Comcast users think they've got it bad? by Ant+P. · · Score: 3, Informative

    The ISP supplying my workplace regularly blocks HTTP for up to hours at a time. Nothing else, just outgoing(!) port 80. First connections get dropped silently, then after a while it moves on to forged TCP reset packets when trying to connect to anything. Which is pretty worrying because they're the only ISP available here.

  8. Not a "Catch-22" by Lord+Byron+II · · Score: 5, Insightful

    "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.

  9. Not agnostic by Ghworg · · Score: 5, Insightful

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

  10. Because then their service would be a commodity by Geof · · Score: 4, Insightful

    Bandwidth is a commodity. As such is interchangeable: the provider of a commodity is in competition with everyone else providing the same commodity. They have to differentiate themselves based on price, which they can only do by cutting costs and increasing efficiency. Though market competition is in our best interests as consumers, it isn't in theirs. The last thing a company wants is for market competition to work efficiently to drive down their margins. That's why they will do everything they can to avoid selling a commodity: product differentiation, branding, and so on - strategies that effectively create mini monopolies (you don't buy an MP3 player, you buy an iPod; you don't buy shoes, you buy Nike).

    That's the main reason. Another, which applies especially to monopolies (hello telecoms!), is price discrimination. A company would like to charge each customer as much as that customer can afford to pay, but they don't want to lose business with a price that's too high. By developing different classes of service they can coax more money from those able to pay more. The classic example is first-class seating on flights. How much a customer is able to pay may also depend on how much the service is worth to them. It may not cost the telecom company any more to provide bandwidth for, say, VoIP users than for WoW players, but VoIP customers may be able to pay more because it saves them money elsewhere.

    It is the role of good market regulation to ensure competition works effectively to drive prices down towards costs. That is broadly good for consumers and for the economy as a whole. Companies - especially incumbent companies - should be expected to do everything in their power to fight to break the market. And they do.

  11. VOIP!=Internet by not_anne · · Score: 5, Informative

    "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

    --
    My comments here are my own; I do not speak for my employer.
  12. You should know... by AliasMarlowe · · Score: 5, Insightful

    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.

    --
    Those who can make you believe absurdities can make you commit atrocities. - Voltaire