When I stream video over my DSL internet, why does the quality fluctuate dramatically?

Episode 882 (15:03)

Alan from Simi Valley, CA

This has to do with the speed of the connection he's getting from his internet provider. When the provider quotes a number for speed, they're giving the upper number, or the fastest it could be. DSL, in Leo's experience, is generally more consistent than cable internet, though. Some internet providers have a little trick they use called "burst mode", which means they give real fast internet when first connecting, but then slows down. Leo says he could call AT&T and go a tier higher in internet speed, which would cost around $10 a month more.

There are a number of issues that could contribute to Alan's fluctuating video quality:

  • Internet speed inconsistency.
  • Alan's internet could be fluctuating in speed, requiring the video to drop down to a lower quality to continue playing. Most video will do this instead of stopping entirely. One type of internet that's consistently fast is Verizon FiOS, but they aren't rolling it out anymore and Alan may not have this as an option.

  • Latency, jitter, and lag.
  • These are things people don't generally pay attention to, but Alan may be experiencing this too. This might not be evident while watching TV since it is all downstream, but could be more of an issue while using Skype. He may notice lag between him and the person on the other end.

  • Buffer bloat.
  • A "buffer" is when the video or audio player downloads the media ahead of time, and then starts playing it. If it can't load more of that media, the buffer will go down to zero, and the video will pause while it loads more. Routers do the same thing, with internal memory. When memory got very cheap, router manufacturers starting putting more memory in to accommodate a larger buffer. The problem is, they're putting so much memory in for buffer that it's breaking TCP congestion control which is designed to handle this problem without resorting to giant buffers.

    Alan could diagnose this problem with Netalyzr. Essentially, he'll want everything to show up green. If something shows up red, that means there are internet access issues. He'll want to pay attention to the "Network Access Link Properties". If the report shows yellow or red under "Network Buffer Management", then it's not the service provider, it's an issue with his router. Then he may want to get a new router, but there's no information right now to determine which routers have less of a buffer bloat problem than others

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