Download - Effekterna av bufferbloat och latency på internet

Are you feeling buffer bloated?Stefan Holmer

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


Turns out...

● ...someone is streaming a movie or downloading a big file.

● ...not necessarily in your home.

● ...it's not necessarily lack of bandwidth.


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)

http://chimera.labs.oreilly.com/books/1230000000545/ch02.html#SLOW_START


TCP - Roughly Fair


Effects of a Long TCP Transfer

(Jim Gettys' measurements)

http://gettys.wordpress.com/2010/12/06/whose-house-is-of-glasse-must-not-throw-stones-at-another/


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


Bufferbloat

● Memory cheaper and cheaper.● Bigger buffers are added to avoid losing packets.● TCP needs those losses!


Slow-start will really be slow

(from, Ilya Grigorik's blog, igvita.com)

https://www.igvita.com/2012/07/19/latency-the-new-web-performance-bottleneck/


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.


Check your home connection

● Try Netalyzr.

● Measures the quality of your connection in terms of:○ Blocked ports○ Throughput○ Queue sizes/bufferbloat


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