Let's make TCP faster

Transmission Control Protocol (TCP), the workhorse of the Internet, is designed to deliver all the Web’s content and operate over a huge range of network types. To deliver content effectively, Web browsers typically open several dozen parallel TCP connections ahead of making actual requests. This strategy overcomes inherent TCP limitations but results in high latency in many situations and is not scalable.

Our research shows that the key to reducing latency is saving round trips. We’re experimenting with several improvements to TCP. Here’s a summary of some of our recommendations to make TCP faster:

1. Increase TCP initial congestion window to 10 (IW10). The amount of data sent at the beginning of a TCP connection is currently 3 packets, implying 3 round trips (RTT) to deliver a tiny 15KB-sized content. Our experiments indicate that IW10 reduces the network latency of Web transfers by over 10%.

2. Reduce the initial timeout from 3 seconds to 1 second. An RTT of 3 seconds was appropriate a couple of decades ago, but today’s Internet requires a much smaller timeout. Our rationale for this change is well documented here.

3. Use TCP Fast Open (TFO). For 33% of all HTTP requests, the browser needs to first spend one RTT to establish a TCP connection with the remote peer. Most HTTP responses fit in the initial TCP congestion window of 10 packets, doubling response time. TFO removes this overhead by including the HTTP request in the initial TCP SYN packet. We’ve demonstrated TFO reducing Page Load time by 10% on average, and over 40% in many situations. Our research paper and internet-draft address concerns such as dropped packets and DOS attacks when using TFO.

Read more: Google code blog
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