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

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.

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)

Google Confidential and Proprietary

TCP - Roughly Fair

Google Confidential and Proprietary

Effects of a Long TCP Transfer

(Jim Gettys' measurements)

Google Confidential and Proprietary

Effects of a Long TCP Transfer

(Jim Gettys' measurements)

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

Google Confidential and Proprietary

Bufferbloat

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

Google Confidential and Proprietary

Slow-start will really be slow

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

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.

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

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