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Wireless Networking Cellphones Communications Networking

A Possible Cause of AT&T's Wireless Clog — Configuration Errors 217

Posted by timothy
from the three-card-monty-design dept.
AT&T customers (iPhone users notably among them) have seen some wireless congestion in recent months; Brough Turner thinks the trouble might be self-inflicted. According to Turner, the poor throughput and connection errors can be chalked up to "configuration errors specifically, congestion collapse induced by misconfigured buffers in their mobile core network." His explanation makes an interesting read.
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A Possible Cause of AT&T's Wireless Clog — Configuration Errors

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  • by dziman (415307) on Sunday October 25, 2009 @10:20PM (#29868563)

    I don't believe AT&T is the cheapest provider.

  • by socsoc (1116769) on Sunday October 25, 2009 @10:26PM (#29868599)

    They are far from the cheapest. MetroPCS and those other all you can eat plans are the cheapest, now they even include international calling.

    One reason people are still with AT&T is of course the iPhone, but also the locked carrier status on phones in the United States in general.

  • by hitmark (640295) on Sunday October 25, 2009 @10:27PM (#29868605) Journal

    quality, and fashion, one not having to be the other...

  • by MBCook (132727) <foobarsoft@foobarsoft.com> on Sunday October 25, 2009 @10:34PM (#29868649) Homepage

    Wow. This is kind of amazing.

    Nothing on this page (as I type) talks about zero packet loss, except you. That means you read the article.

    Of course, the article says that AT&T has set their buffers large enough to prevent packet loss due to congestion in transit, not that they expect no radio packet loss. The problem is that TCP/IP needs packet loss to tell it when it's going too fast and AT&T's decision causes this to fail spectacularly at times.

    The trolls read the articles. Weird.

  • Non-obvious cause (Score:5, Informative)

    by NixieBunny (859050) on Sunday October 25, 2009 @10:58PM (#29868737) Homepage
    If you take the time to RTFA, you will see that the problem with TCP management (as Mr. Turner describes it) is that you have to cause the system to drop packets occasionally when it's near but not quite at saturation, to let the TCP device at the other end know that the network is getting congested. If there are no dropped packets, TCP ups the packet rate until the network becomes clogged.

    So in this case, zero packet loss is a setup for disaster instead of a desirable quality.

    The trouble is that it's not an intuitive solution to a problem, the introduction of occasional packet loss. It's usually something to avoid.

  • Re:Hm (Score:3, Informative)

    by Anonymous Coward on Sunday October 25, 2009 @11:54PM (#29868943)

    Because they don't monitor it. They don't even send a guy to check on it unless several people on the same cell log a complaint, something which may take several calls to customer service.

  • Router fairness (Score:5, Informative)

    by Animats (122034) on Monday October 26, 2009 @12:24AM (#29869033) Homepage

    TCP measures round trip time, and doesn't need packet loss to tell it that the round trip time is long. The retransmit interval will go up appropriately. TCP will behave reasonably with a long round trip time. If you're trying to do a bulk transfer, there's nothing wrong with this. The problem comes when short messages and bulk transfers are sharing the same channel. The short messages can spend too much time in the queue.

    The solution is reordering the packets, not dropping them. That's what "fair queuing" is about. It may be worthwhile to implement fairness at the port-pair level, rather than the IP address level, at entry to the air link. Then low-traffic connections will get through faster.

    "Quality of service" can help, but it's not a panacea. The network layer can't tell which of the TCP connections on port 80 is highly interactive and which is a bulk download, other than by traffic volume.

    (I used to do this stuff [faqs.org].)

  • by Not_Wiggins (686627) on Monday October 26, 2009 @12:38AM (#29869083) Journal
    I presume you have an iPhone. A friend of mine that has jailbroken his phone pointed out to me that the bars represent the 3G signal strength, and not necessarily the regular network strength. I was considering AT&T because the T-Mobile strength in my house is terrible. He had 3-4 bars on his IPhone, but when he turned off 3G and went to EDGE only, it averaged 1-2 bars. Point is, I don't think the signal strength always means what we think it means. 8/
  • by Rakshasa Taisab (244699) on Monday October 26, 2009 @12:43AM (#29869097) Homepage
    Sorry, but the thing about Europe is bullshit. The macbooks are so popular in Norway that pretty much _everyone_ in university has one. And I'm not saying 'everyone' as in 20%, but literally almost everyone.
  • by socsoc (1116769) on Monday October 26, 2009 @12:49AM (#29869129)
    Cause they aren't necessarily the same tower? Your scenario makes perfect sense. Except that jailbroken has nothing to do with it and if you are getting 3G signal, that is your "regular network strength." It only degrades to EDGE if you can't get a 3G signal (which for my major metropolitan area, is nearly any building you walk into).
  • by mveloso (325617) on Monday October 26, 2009 @01:12AM (#29869181)

    1. the US is much bigger than Europe, with multiple overlapping jurisdictions. It's easy to cover any of the European countries, because they're small and there wasn't a technology transition.

    2. there isn't as much rural subsidy for cellphones. Universal service was for landlines, mainly.

    3. the problem is cost vs coverage. You can build out rural areas, but you make less money because there are less people. For urban areas, you start running into interference problems. Plus, you have to constantly build out your infrastructure (see AT&T's infrastructure problems).

    Europe has it easy. It's not evil corporations (which, to be frank, is a retarded and simplistic view of how things work) - it's pure cost/benefit.

    Example:

    France: 211,207 square miles
    Texas: 268,601 square miles
    US: 3,537,441 square miles

    If AT&T only had to operate in Texas, it would be able to do pretty well. AT&T's footprint is national, however. Do you develop Texas completely, or do you cover Michigan and Texas? How about extending to Missouri? etc etc.

    Then that's current coverage; what about LTE? How about maintaining that infrastructure?

  • Re:Router fairness (Score:3, Informative)

    by Trepidity (597) <delirium-slashdot@@@hackish...org> on Monday October 26, 2009 @02:12AM (#29869481)

    I was about to post a comment on this article complaining that "TCP doesn't work unless routers drop packets" is oversimplifying how TCP works at best, partly by citing RFC 896, then I come and see the author of the damn RFC beat me to it. This discussion in the article of buffers so large that they never fill (so can in effect be considered infinite) makes RFC 970 [faqs.org] seem relevant, also.

  • by SuperKendall (25149) on Monday October 26, 2009 @03:05AM (#29869723)

    I'm not sure Apple products are of better quality than your average branded PC.

    Consumer satisfaction surveys say otherwise. My own experience with multiple PC's and Macs also say otherwise...

    It's also not that Macs never break, it's that dealing with Applecare is so much nicer than any other computer support agency. When I say "product", I mean the whole package and not just the hardware.

  • by SuperKendall (25149) on Monday October 26, 2009 @03:17AM (#29869779)

    apple was on the death bed, until the ipod got fashionable

    Two things wrong here:

    1) Apple had already seen a comeback from the iMacs at this point. Jobs had been back for a few years and the company was growing steadily. They were far away from "deathbed" status at this time.

    2) The iPod didn't grow because it was fashionable. I bought one of the first ones because it was literally an order of magnitude faster to load songs onto than any other player at the time - and the interface was far better. The transfer speeds evened out but I never saw another MP3 player I liked as much for just everyday use. The iPod exploded in popularity mostly because of functionality, not fashion - the first of them were too bulky to really be considered fashionable.

    but then this also depends heavily on where in the world one lives. USA seems basically saturated with apple (and thanks to the majority of the tech blogs being run out of USA, that gives a "interesting" slant on things), while europe seems to be mostly wintel

    Europe is more wintel, but Apple marketshare grows there as well. I just was in Budapest an an Apple store there was doing very well... marketshare is a tricky thing because it's masked by business PC purchases, so you don't know what real-world marketshare is with people that live with computers, not the computers that are handed down to them from on high.

    There is however the "new market", that is unix geeks that basically use osx for its bsd kernel and shell.

    There's nothing new at all about this market. This core group of users is how Apple actually grew OS X from the beginning, because these people were the technical friends people looked to for computer advice, and they told friends and family "buy a mac". In part this was selfish because they knew they would have to help the users far less, but it's also in the end better for users that need help less often.

    I would say that if HP or dell really took a good look at linux, or even one of the BSD's, they could match apple on quality.

    HP used to have the potential to do that but I have a lot of doubts at this point in time, mostly because HP has shredded itself. Linux does need a champion to really tighten up the whole thing and then it has a lot of potential, but I'm not sure I see the company around right now that can do that.

  • by Savage650 (654684) on Monday October 26, 2009 @04:02AM (#29869949)

    My phone almost always shows five bars at home, yet frequently calls don't cause the phone to ring - they go to voicemail after pretending to ring. The jaded amongst us could suspect a deliberate misconfiguration of phones and signal strength monitoring.

    Signal strength alone does not guarantee the ability to make/receive calls. Even if your mobile is registered in the network, making and receiving calls depends on the availability of various scarce resources, namely:

    1. a "slot" on the over-the-air network (# of active connections per cell is limited)
    2. a "switching path" inside your operators network
    3. a "switching path" inside one or more transfer networks (owned by someone else)
    4. a "switching path" inside the network the caller/callee is connected to
    5. a "slot" on the over-the-air network on the others side (if the caller/callee is mobile)

    In case of "lots of missed calls" in a particular area (your home) one could assume that

    • your home cell is overcrowded (all slots in use) or
    • there is a bottleneck in the upstream network

    Note: outgoing calls should have the same problems; if they "fail less" it could be because your operator has chosen to reserve a (possibly large?) percentage of the slots/lines for outgoing calls. (Which obviously reduces the chances of incoming calls even more)

  • Re:Router fairness (Score:3, Informative)

    by complete loony (663508) <Jeremy,Lakeman&gmail,com> on Monday October 26, 2009 @07:46AM (#29870849)

    When TCP receives an ACK it can dump it's whole window size of packets onto the wire. A large number of TCP streams sharing a link with large transmit buffers and a small common bottleneck will saturate your transmit buffers. Yes TCP will tend to back off. But when you have heaps of streams all trying to transmit data, they collectively try to ramp up again too quickly.

    I used to share an ADSL link with a neighbour of mine. I would often see the round trip latency over the ADLS link and back go up to 1 to 1.5 seconds with a bittorrent client running a bunch of TCP streams. So we put a hard upper limit on the transmit rate of his BSD router so the ADSL modem could never fill up its transmit buffer and most of the problem went away.

  • Re:First Time (Score:3, Informative)

    by umghhh (965931) on Monday October 26, 2009 @12:39PM (#29873791)
    I was on the other side of the divide than you number of times and I must say I can understand the trade-offs well enough for an idiot techie. I have great doubts that this is the same on your time of the divide though.

    I make it simple for you as you are obviously on the other side. There are basically 3 basic ways to save money while doing a project and consequently 4 different decisions you can make:

    • not doing a project at all. In absolute terms it is a bummer - no costs! It has a disadvantage of not having a product at the end
    • doing the project good enough for a management i.e. saving too much to have a working product. The good thing is you have a product. Bad that you do not have a product for which you can honestly claim any money.
    • doing the project good enough for both sides of the divide i.e. techie and manager idiots. This is as said good enough on the level all others deliver.
    • doing the project well. This has disadvantage of being costly but may have an advantage of being possible to ask for a premium for a good product.Another advantage is for projects to come so in simplistic vision visible for a simpletons that make decisions usually not visible at all: design base is good so you save on design costs.

    OC last option does not work on a market where nobody is willing to pay that premium and where consequently there is nobody delivering this better quality so nobody even knows that one can do better. That is especially true in situations where customer does not care as long as the product KOW (kind of works) and its inadequacies and suffering they cause is by somebody else while at the same time barrier to entry is high enough to prevent real competition. What is really appalling is that people do not understand consequences of their actions choosing suboptimal but cheap product and wondering why it does not work.

    Bottom line is a definition of where the point of 'good enough' is - neither financial nor technical expertise only are sufficient to make a good decision, consequences are usually hanging on techie necks after bonies have been consumed by managers though. Justification for direct action at least in some cases one may think.

  • by dgatwood (11270) on Monday October 26, 2009 @01:27PM (#29874429) Journal

    The locked phones come as a consequece of people wanting cheap phones (subsidized, they call them).

    If that were the case, you could easily buy unsubsidized phones in the U.S. At least on Verizon, that isn't even an option. They won't sell you a phone without moving to a new contract, often at a higher rate with fewer minutes or reduced features. That's why I ended up on AT&T. Similarly, if the high cost were due to people wanting cheap phones, we would get a rate cut after the subsidy period like they do in Europe.

    The locked phones come as a consequence of the cell service providers seeing an opportunity for customer lock-in and taking advantage of it to the maximum extent possible. Nothing more, nothing less.

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