[tcpm] Problem with Low SSThresh (was I-D Action: draft-ietf-tcpm-newcwv-03.txt)
Ingemar Johansson S <ingemar.s.johansson@ericsson.com> Tue, 13 May 2014 08:15 UTC
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From: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
To: "tcpm@ietf.org" <tcpm@ietf.org>
Thread-Topic: Problem with Low SSThresh (was I-D Action: draft-ietf-tcpm-newcwv-03.txt)
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Date: Tue, 13 May 2014 08:15:19 +0000
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Archived-At: http://mailarchive.ietf.org/arch/msg/tcpm/jhrp5jxuCbe8TO69ICNhUSdEReA
Subject: [tcpm] Problem with Low SSThresh (was I-D Action: draft-ietf-tcpm-newcwv-03.txt)
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Hi Karen pointed out this thread to me http://www.ietf.org/mail-archive/web/tcpm/current/msg08315.html I started to look closer at this issue quite recently, the problem I have is that SSthresh can drop to very low values after only a few lost packets. I have seen this odd effect earlier but have not bothered with it. The experiment is to run a large FTP transfer over a 1Mbps bottleneck with min RTT = 40ms. No AQM or tail drop queue enabled i.e a buffer bloated scenario. TCP NewReno. After 10s I "pull the plug" for 100ms (100% packet drop), this leads to 5 lost segments. at T =10.1s packets are forwarded as usual. What I have seen is that a retransmission timeout is immediately followed by a loss event, the effect of which is that SSThresh goes down to 2 MSS. It seems to me that the RTO timer value is too low, I have not understood the effect completely though. Could the RTO timer be the culprit or is there some other effect ?. I am running these experiments in a proprietary LTE system simulator, we try to keep it up to date to match the Linux TCP stack reasonably well, it cannot be ruled out however that our implementation miss some important feature. /Ingemar ================================= Ingemar Johansson M.Sc. Senior Researcher Ericsson AB Wireless Access Networks Labratoriegränd 11 971 28, Luleå, Sweden Phone +46-1071 43042 SMS/MMS +46-73 078 3289 ingemar.s.johansson@ericsson.com<mailto:ingemar.s.johansson@ericsson.com> www.ericsson.com "Those are my principles, and if you don't like them... well, I have others." Groucho Marx<http://www.brainyquote.com/quotes/authors/g/groucho_marx.html> =================================
- [tcpm] Problem with Low SSThresh (was I-D Action:… Ingemar Johansson S
- Re: [tcpm] Problem with Low SSThresh (was I-D Act… Raffaello Secchi
- Re: [tcpm] Problem with Low SSThresh (was I-D Act… McAlpine, Gary
- Re: [tcpm] Problem with Low SSThresh (was I-D Act… Gorry Fairhurst
- Re: [tcpm] Problem with Low SSThresh (was I-D Act… Ingemar Johansson S