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colmmacc's profile
Colm MacCárthaigh
Colm MacCárthaigh
Colm MacCárthaigh
@colmmacc

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Colm MacCárthaigh

@colmmacc

AWS, Apache, Crypto, Irish Music, Haiku, Photography

Seattle
notesfromthesound.com
Joined April 2008

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    1. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      The modern form of this is selective acknowledgements (SACK) ... where we can basically just scribble a note back on the sushi belt that tells the sender "hey, here's what I got and didn't get". The sender than re-transmit only what it needs to.

      1 reply 2 retweets 12 likes
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    2. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      So if you do those two things: make your window size big, and make sure selective acknowledgements are on, you can make a big difference to your performance! That video can get to you more quickly.

      1 reply 2 retweets 12 likes
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    3. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      Of course we do this kind of stuff ourselves for our own services, but if you're transferring data between your own machines or whatever, take a look!

      1 reply 0 retweets 10 likes
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    4. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      now let's extend the model: I said that a pipe or link is like a sushi belt, but there are lots of links interconnecting! So it's like a stadium full of sushi belts, with packets hopping belts. It's like Tim Burton and the Coen brothers made a movie together.

      1 reply 0 retweets 11 likes
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    5. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      when the belts interconnect, they might be moving at different speeds, or one might have less capacity than the other, so we have little holding areas, we call these "buffers".

      1 reply 0 retweets 6 likes
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    6. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      Generally packets enter and leave these buffers in order, but in some networks you can have priority lanes here, giving priority to some packets over others. At AWS, our belts move so quickly and there are so many free slots that we don't need to do this, it'd be pointless.

      1 reply 0 retweets 7 likes
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    7. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      But if there is congestion, and slots are busy, it's because senders are sending too much; it's key that they know quickly, so we make these buffers small. The problem of having these buffers too big is called buffer bloat (https://www.bufferbloat.net/projects/bloat/wiki/What_can_I_do_about_Bufferbloat/ …)

      2 replies 2 retweets 11 likes
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    8. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      This can all be very confusing without the right mental model. Because we generally want one kind of buffer - the window size - to be big, but another kind of buffer - the buffers between links - to be small.

      1 reply 0 retweets 7 likes
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    9. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      But if you see the network as train-cars or sushi on a belt, what you can see is that what we *really* want is to fill as many slots as we can when we're sending data! That's really all that's going on.

      1 reply 0 retweets 5 likes
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    10. Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      One problem with the metaphor: packets don't actually go in loops, they come at the other end, so unlike a sushi belt, there's a kind of off-ramp at each end. Also packets only enter and exit at the ends. There's really no perfect metaphor.

      1 reply 1 retweet 11 likes
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      Colm MacCárthaigh‏ @colmmacc 22 Feb 2019
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      I'm going to meditate on better metaphors, so that's it for now :)

      4:04 PM - 22 Feb 2019
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      • Adrian Mihailov ‏pix Robert Devereux Venkatarangan Thirumalai Dov Murik Philipp Meier Sahil Ajay Andy Fowler
      13 replies 1 retweet 31 likes
        1. Abby Fuller‏ @abbyfuller 22 Feb 2019
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          Replying to @colmmacc

          I need sushi now.

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        1. Pranesh Prakash‏Verified account @pranesh 22 Feb 2019
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          Valiant attempt! I only started understanding this stuff once I started using OpenWrt and thanks to that got the impetus to learn about stuff like bufferbloat. How would you explain bandwidth with this analogy? I like "each packet goes as fast as it can until it hits congestion".

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        1. Joe Magerramov‏ @_joemag_ 22 Feb 2019
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          Replying to @colmmacc

          You needed to “drop” one of the tweets in the thread to drive the point...

          0 replies 0 retweets 1 like
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        1. New conversation
        2. Marc Olson‏ @molson 22 Feb 2019
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          Replying to @colmmacc

          TTL exceeded

          1 reply 0 retweets 1 like
        3. Matt Johnson‏ @mhj_work 23 Feb 2019
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          Replying to @molson @colmmacc

          “Best before” date on each of the sushi rolls :)

          0 replies 0 retweets 0 likes
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        2. Jason Bordujenko‏ @kinshasha 22 Feb 2019
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          Replying to @colmmacc

          Great series! @threadreaderapp please help unroll

          1 reply 0 retweets 0 likes
        3. Thread Reader App‏ @threadreaderapp 22 Feb 2019
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          Replying to @kinshasha

          Hello please find the unroll here: Thread by @colmmacc: "O.k. time for a mini-tweet thread which is all about network and TCP optimization! How can we make connections fast and […]" https://threadreaderapp.com/thread/1099086415671877633.html … Have a good day. 🤖

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        2. Stefano Buliani‏ @sapessi 22 Feb 2019
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          Replying to @colmmacc

          I was about to say dabbawallas but I can't come with anything for the ack

          1 reply 0 retweets 0 likes
        3. Stefano Buliani‏ @sapessi 22 Feb 2019
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          Replying to @sapessi @colmmacc

          Except for empty food containers coming back

          0 replies 0 retweets 0 likes
        4. End of conversation
        1. «Darlene»‏ @JulieCook_Cyber 23 Feb 2019
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          Replying to @colmmacc

          It’s so complicated and this happens all in a matter of seconds. Packets and Datagrams can become confusing in the CSPverse. Windows and Buffer size would be a useful infographic to maximize speed and reliability. We’re learning something new everyday! 😊 thank you!

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