TCP: Google Looks to Speed Up the Internet

TCP: Google Looks to Speed Up the Internet
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Google researchers want to overhaul the Internet’s Transmission Control Protocol (TCP) transport layer and have suggested ways to reduce latency. According to the company’s Make the Web Faster team, the key to reducing latency is saving round trips. The researchers recommend increasing the TCP initial congestion window to improve TCP speed. “The amount of data sent at the beginning of a TCP connection is currently three packets, implying three round trips to deliver a tiny, 15K-sized content,” says Google’s Yuchung Chen.

“Our experiments indicate that IW10 [initial congestion window of 10 packets] reduces the network latency of Web transfers by over 10 percent.” Google also wants the initial timeout reduced from three seconds to one second. The company has developed the TCP Fast Open protocol, which reduces application network latency, and proportional rate reduction for TCP, and the team is encouraging its use. Google’s work is open source and disseminated through the Linux kernel, Internet Engineering Task Force standards proposals, and research publications to encourage industry involvement.

Here’s a summary of some of Google’s 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.

4. Use Proportional Rate Reduction for TCP (PRR). Packet losses indicate the network is in disorder or is congested. PRR, a new loss recovery algorithm, retransmits smoothly to recover losses during network congestion. The algorithm is faster than the current mechanism by adjusting the transmission rate according to the degree of losses. PRR is now part of the Linux kernel and is in the process of becoming part of the TCP standard.

In addition, we are developing algorithms to recover faster on noisy mobile networks, as well as a guaranteed 2-RTT delivery during startup. All our work on TCP is open-source and publicly available. We disseminate our innovations through the Linux kernel, IETF standards proposals, and research publications. Our goal is to partner with industry and academia to improve TCP for the whole Internet. Please watch this blog and http://code.google.com/speed/ for further information.”

Source: Google via TechNews

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