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Your feeling is spot on. They definitely burst to a higher speed at the beginning of a transfer. What’s really amazing is that they’re proud of it! https://corp

Your feeling is spot on. They definitely burst to a higher speed at the beginning of a transfer. What’s really amazing is that they’re proud of it! https://corporate.comcast.com/comcast-voices/what-is-powerboost https://corporate.comcast.com/comcast-voices/what-is-powerbo...

rayiner 7y ago
Apple and Intel seem pretty proud of their burst speeds too. (And battery life, which is quoted based on running the CPU at short bursts and then going idle.) And why shouldn’t they be? Consumer tech is properly optimized for burst usage. The network delivers the 10MB home page in a burst, then goes idle. The CPU bursts to 4 GHz to render it as fast as possible, then goes idle. The battery delivers 35W for half a second, then drops down to 5W. The whole system is designed around that usage profile.
- mikeash 7y ago
  The difference is that CPUs burst above the speed they can sustain. The alternative would be running slower all the time. Comcast, in contrast, just lets you use more of their otherwise idle capacity, then throttles you. The alternative would be getting the full capacity of their network all the time.
  - rayiner 7y ago
    Looking at the description in the article: > This team discovered that at any given time there was some unused capacity in our network that could be used to temporarily enable faster connection speeds. PowerBoost was born. TurboBoost notices there is additional thermal/power headroom, and boosts until that headroom is gone. PowerBoost seems very similar, except it's based on using unused capacity. The tapering is necessary, because PowerBoost uses up that excess capacity. The network tapers users off after the boost so there is excess capacity for other users to have a higher boost.
    - mikeash 7y ago
      It’s only a zero-sum game when their network is at 100% capacity. If they were playing games to optimize usage at peak times I might not care (although they should increase capacity in that case) but when they do this at 5AM it’s clearly bullshit. I don’t understand why you’re carrying Comcast’s water here. Nobody else does this nonsense. My FiOS connection is a gigabit all day every day. This isn’t a clever bit of network management that gives them an edge. It’s a clever bit of marketing which also allows them to cheat on speed tests. “The tapering is necessary, because PowerBoost uses up that excess capacity.” What the heck!? The network isn’t some kind of battery. There’s no buffer that gets filled up after 20MB on a TCP stream and they have to slow down to let it drain. I know you’re smarter than this.
      - rayiner 7y ago
        > It’s only a zero-sum game when their network is at 100% capacity. If they were playing games to optimize usage at peak times I might not care (although they should increase capacity in that case) but when they do this at 5AM it’s clearly bullshit. I don't know exactly how PowerBoost works. I'm going off the description in the article you linked. The article says that PowerBoost uses up excess capacity on the network when it's available. It follows that you can't PowerBoost everybody, even at non-peak times, without lowering the maximum amount of boost. > I don’t understand why you’re carrying Comcast’s water here. Nobody else does this nonsense. No offense, but to most people on HN the physical network is an abstraction that magically delivers bits from point A to point B, and they say crazy things like "networks shouldn't be oversubscribed." I spent my engineering career sitting around layers 2/3, so reading this stuff tends to put me into rant mode.
        mikeash 7y ago
        The article I linked is a PR piece. Don’t get technical details from it. I linked to it just to show how they’re proud of their bullshit. Here’s some better info: https://www.dslreports.com/faq/14520 https://www.dslreports.com/faq/14520 Relevant quote: “PowerBoost provides bursts for the first 20 MB downloading and the first 10 MB uploading of a file respectively on select Comcast High-Speed Internet services.” Surely you admit that there is no sensible technical reason for a magic 20MB per-file limit on this.

rayiner 7y ago

Apple and Intel seem pretty proud of their burst speeds too. (And battery life, which is quoted based on running the CPU at short bursts and then going idle.) And why shouldn’t they be? Consumer tech is properly optimized for burst usage. The network delivers the 10MB home page in a burst, then goes idle. The CPU bursts to 4 GHz to render it as fast as possible, then goes idle. The battery delivers 35W for half a second, then drops down to 5W. The whole system is designed around that usage profile.

mikeash 7y ago
The difference is that CPUs burst above the speed they can sustain. The alternative would be running slower all the time. Comcast, in contrast, just lets you use more of their otherwise idle capacity, then throttles you. The alternative would be getting the full capacity of their network all the time.
- rayiner 7y ago
  Looking at the description in the article: > This team discovered that at any given time there was some unused capacity in our network that could be used to temporarily enable faster connection speeds. PowerBoost was born. TurboBoost notices there is additional thermal/power headroom, and boosts until that headroom is gone. PowerBoost seems very similar, except it's based on using unused capacity. The tapering is necessary, because PowerBoost uses up that excess capacity. The network tapers users off after the boost so there is excess capacity for other users to have a higher boost.
  - mikeash 7y ago
    It’s only a zero-sum game when their network is at 100% capacity. If they were playing games to optimize usage at peak times I might not care (although they should increase capacity in that case) but when they do this at 5AM it’s clearly bullshit. I don’t understand why you’re carrying Comcast’s water here. Nobody else does this nonsense. My FiOS connection is a gigabit all day every day. This isn’t a clever bit of network management that gives them an edge. It’s a clever bit of marketing which also allows them to cheat on speed tests. “The tapering is necessary, because PowerBoost uses up that excess capacity.” What the heck!? The network isn’t some kind of battery. There’s no buffer that gets filled up after 20MB on a TCP stream and they have to slow down to let it drain. I know you’re smarter than this.
    - rayiner 7y ago
      > It’s only a zero-sum game when their network is at 100% capacity. If they were playing games to optimize usage at peak times I might not care (although they should increase capacity in that case) but when they do this at 5AM it’s clearly bullshit. I don't know exactly how PowerBoost works. I'm going off the description in the article you linked. The article says that PowerBoost uses up excess capacity on the network when it's available. It follows that you can't PowerBoost everybody, even at non-peak times, without lowering the maximum amount of boost. > I don’t understand why you’re carrying Comcast’s water here. Nobody else does this nonsense. No offense, but to most people on HN the physical network is an abstraction that magically delivers bits from point A to point B, and they say crazy things like "networks shouldn't be oversubscribed." I spent my engineering career sitting around layers 2/3, so reading this stuff tends to put me into rant mode.
      - mikeash 7y ago
        The article I linked is a PR piece. Don’t get technical details from it. I linked to it just to show how they’re proud of their bullshit. Here’s some better info: https://www.dslreports.com/faq/14520 https://www.dslreports.com/faq/14520 Relevant quote: “PowerBoost provides bursts for the first 20 MB downloading and the first 10 MB uploading of a file respectively on select Comcast High-Speed Internet services.” Surely you admit that there is no sensible technical reason for a magic 20MB per-file limit on this.