Effekterna av bufferbloat och latency på internet

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Stefan Holmer, Google
Var uppkommer latency på internet och vilka effekter leder det till? Hur kan framtidens internet lösa problemet? Vad kan man som applikationsutvecklare göra för att förbättra situationen?

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Effekterna av bufferbloat och latency på internet

  1. 1. Are you feeling buffer bloated? Stefan Holmer
  2. 2. Google Confidential and Proprietary App performs poorly for some users ● Simple tasks are taking seconds to perform: ○ Downloading a web page ○ Sending a message ○ DNS queries are timing out ● Interactivity is completely broken: ○ Calling doesn't work due to talking over each other ○ Gaming gets frustrating
  3. 3. Google Confidential and Proprietary Turns out... ● ...someone is streaming a movie or downloading a big file. ● ...not necessarily in your home. ● ...it's not necessarily lack of bandwidth.
  4. 4. Google Confidential and Proprietary Taking a Step Back - TCP Loss based ○ Wants to keep increasing the bitrate (cwnd) until a packet is lost. ○ Typically happens when a packet buffer is full. (from Ilya Grigorik's High Performance Browser Networking)
  5. 5. Google Confidential and Proprietary TCP - Roughly Fair
  6. 6. Google Confidential and Proprietary Effects of a Long TCP Transfer (Jim Gettys' measurements)
  7. 7. Google Confidential and Proprietary Effects of a Long TCP Transfer (Jim Gettys' measurements)
  8. 8. Google Confidential and Proprietary Bufferbloat ● In the early days, buffers were reasonably sized. ● TCP got feedback early when the link was over-used. ● Packet loss = bad connection... Queue length
  9. 9. Google Confidential and Proprietary Bufferbloat ● Memory cheaper and cheaper. ● Bigger buffers are added to avoid losing packets. ● TCP needs those losses!
  10. 10. Google Confidential and Proprietary Slow-start will really be slow (from, Ilya Grigorik's blog, igvita.com)
  11. 11. Google Confidential and Proprietary What can we do? ● In applications, mostly nothing. This is something others do to you! ○ Avoid big TCP transfers when interaction is needed. ○ Limit background traffic. ● Must be solved: ○ in the network. ○ or in every endpoint. ● Notify people when possible.
  12. 12. Google Confidential and Proprietary Check your home connection ● Try Netalyzr. ● Measures the quality of your connection in terms of: ○ Blocked ports ○ Throughput ○ Queue sizes/bufferbloat
  13. 13. Google Confidential and Proprietary What is being done? ● Improving the networks. ○ Lots of research on new Active Queue Management techniques ■ CoDel, PIE ○ Drop packets earlier when possible to keep the bloat low. ○ Being built into home routers and Linux. ● Improving endpoints. ○ Better delay-sensing congestion control. ○ uTorrent - LEDBAT ○ VoIP services, such as Hangouts - RMCAT

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