[157489] in North American Network Operators' Group
Re: Coded TCP
daemon@ATHENA.MIT.EDU (Masataka Ohta)
Wed Oct 24 02:36:52 2012
Date: Wed, 24 Oct 2012 15:35:41 +0900
From: Masataka Ohta <mohta@necom830.hpcl.titech.ac.jp>
To: nanog@nanog.org
In-Reply-To: <CABRP1o92jGpBz2yi+AgCve34TaNgdHT7X3PRjeBY-BoxNp4BHQ@mail.gmail.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
(2012/10/24 12:29), Rodrick Brown wrote:
> "With coded TCP, blocks of packets are clumped together and then
> transformed into algebraic equations that describe the packets. If
> part of the message is lost, the receiver can solve the equation to
> derive the missing data.
Don't do that.
> MIT found that campus WiFi (2%
> packet loss) jumped from 1Mbps to 16Mbps. On a fast-moving train (5%
> packet loss), the connection speed jumped from 0.5Mbps to 13.5Mbps."
If everyone start using TCP with FEC to tolerate 20% of packet
loss with 30% FEC overhead, it will make congestion more severe
that more than 20% of packets will be dropped and effective speed
share of each TCP will be decreased by 30%.
The proper approach against lossy liks is to have link local
retransmissions or FEC.
Masataka Ohta
