RE: [rohc] Congestion window tracking in RoHC-TCP
"Qian Zhang" <qianz@microsoft.com> Mon, 11 March 2002 15:33 UTC
Received: from optimus.ietf.org (ietf.org [132.151.1.19] (may be forged)) by ietf.org (8.9.1a/8.9.1a) with ESMTP id KAA11673 for <rohc-archive@odin.ietf.org>; Mon, 11 Mar 2002 10:33:24 -0500 (EST)
Received: from optimus.ietf.org (localhost [127.0.0.1]) by optimus.ietf.org (8.9.1a/8.9.1) with ESMTP id KAA24070; Mon, 11 Mar 2002 10:30:52 -0500 (EST)
Received: from ietf.org (odin [132.151.1.176]) by optimus.ietf.org (8.9.1a/8.9.1) with ESMTP id KAA24008 for <rohc@optimus.ietf.org>; Mon, 11 Mar 2002 10:30:47 -0500 (EST)
Received: from mail-jpn.microsoft.com (mail-jpn.microsoft.com [207.46.71.29]) by ietf.org (8.9.1a/8.9.1a) with ESMTP id KAA11570 for <rohc@ietf.org>; Mon, 11 Mar 2002 10:30:43 -0500 (EST)
Received: from jpn-imc-01.fareast.corp.microsoft.com ([157.60.4.29]) by mail-jpn.microsoft.com with Microsoft SMTPSVC(5.0.2195.2966); Tue, 12 Mar 2002 00:30:16 +0900
Received: from 157.60.4.29 by jpn-imc-01.fareast.corp.microsoft.com (InterScan E-Mail VirusWall NT); Tue, 12 Mar 2002 00:30:16 +0900
Received: from bjs-msg-01.fareast.corp.microsoft.com ([157.60.72.120]) by jpn-imc-01.fareast.corp.microsoft.com with Microsoft SMTPSVC(5.0.2195.2966); Tue, 12 Mar 2002 00:30:16 +0900
X-MimeOLE: Produced By Microsoft Exchange V6.0.5762.3
content-class: urn:content-classes:message
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Subject: RE: [rohc] Congestion window tracking in RoHC-TCP
Date: Mon, 11 Mar 2002 23:29:20 +0800
Message-ID: <D8B1DF394D228543B41027F0D07F5B1C0126601B@bjs-msg-01.fareast.corp.microsoft.com>
Thread-Topic: [rohc] Congestion window tracking in RoHC-TCP
Thread-Index: AcHIgClx5hIyUXudQVSo0KjFUytakwAZW1Zw
From: Qian Zhang <qianz@microsoft.com>
To: "West, Mark (ITN)" <mark.a.west@roke.co.uk>, "Per Synnergren (EPL)" <Per.Synnergren@epl.ericsson.se>
Cc: rohc@ietf.org
X-OriginalArrivalTime: 11 Mar 2002 15:30:16.0435 (UTC) FILETIME=[A5155430:01C1C911]
Content-Transfer-Encoding: 8bit
X-MIME-Autoconverted: from quoted-printable to 8bit by optimus.ietf.org id KAA24009
Sender: rohc-admin@ietf.org
Errors-To: rohc-admin@ietf.org
X-Mailman-Version: 1.0
Precedence: bulk
List-Id: Robust Header Compression <rohc.ietf.org>
X-BeenThere: rohc@ietf.org
Content-Transfer-Encoding: 8bit
Hi Mark and Per, Thanks for those comments. Please find my comments inline... BR, Qian > Mark wrote: > The core of EPIC(-lite) is the packet generation / profile processing. > The core of TAROC is the congestion window tracking algorithm. > > I don't think that congestion window tracking affects the handling of > the IPv4 IP-ID, since this is in a lower protocol layer and independent > from TCP behaviour (but someone may wish to correct me...) > As Per pointed out, congestion window tracking can improve the performance of window-based LSB encoding. For those fields that will use W-LSB encoding method and need to achieve robustness, include IPv4 IP-ID, using this algorithm can help to improve performance. > > > > Basically congestion window tracking improves the performance of one > > of the encoding methods used in RoHC, namely window-based least > > significant bits encoding. It is also concluded that the robustness > > of the TCP-compression scheme might be affected negatively if the > > congestion window of TCP is under estimated. > > > > Questions. Is it beneficial to use a "congestion window based" > > compression strategy or what is the "real" gain by using TCP window > > estimation? > > > > I'll leave those who understand these things better to give a > quantitative answer, but the intent is to provide a high degree of > robustness, without sacrificing efficiency without needing explicit > feedback. Yes, the intention for congestion window estimation algorithm is to provide a high degree of robustness, without sacrificing efficiency without needing explicit feedback. We had compared the performance of our scheme with the existing schemes, include RFC1144 and RFC2507. Details please find in http://www.research.microsoft.com/users/qianz/draft-ietf-rohc-tcp-taroc- 03.txt. > > > Is the improved compression large enough to compensate for the > > larger complexity in the compressor and/or the eventual loss in > > robustness due to the chance of underestimate the congestion window? > > > > Whilst I was one of those who was very skeptical about this approach (as > you may recall from previous IETFs and mailing-list discussion), it is > hard to construct scenarios where under-estimation is possible. > (My only lingering doubt concerns TCP Eifel...) > Actually we had discussed this issue intensively around August last year. The congestion window estimation algorithm can always over-estimate the TCP congestion window if the TCP stacks following RFC2581. However, even if we may under-estimate the congestion window size, we can still utilize the TCP retransmission mechanism to re-send the incorrect packet and re-build the context information. For the TCP Eifel protocol part, we noticed that there is only the discussion about the Eifel detection algorithm, which allows the TCP sender to detect a posteriori whether it has entered loss recovery unnecessarily. No corresponding window adjustment algorithm had been discussed by now. Anyway, we had added a minimum and a maximum constrain for the estimated result, so that we can make sure that there is a minimum level of robustness, and meanwhile we can avoid sending the context-updating information too many times. > > How "correct" is the window estimation and what happens if the > > window is wrongly estimated (how good is the fallback mechanism)? > > > > If the window is over-estimated you lose efficiency, but remain robust. > If you under-estimate the window you lose robustness. The latter is > the more serious. > Over estimation is much more likely. The question is, what effect will > this have on effiency? Again, I'm unable to put a number on this at the > present moment. > > Even in the case that this approach (the congestion window tracking) > > is the best solution for TCP/IP compression, should it be in the > > standard? > > > > My point of view, at this time is that it should be up to the > > implementers of RoHC if they want to use congestion window tracking > > rather than it becomes a standard. Hence, it might be explained in > > an implementation issues chapter. Reason: "the bits in the air" > > are not influenced by the use or no-use of congestion window > > tracking. The motive to make something a standard must be: is the > > method absolutely vital to guarantee functionality. > > > > This is an interesting point. It is certainly true that it only affects > the implementation of the compressor. I'm sure others have an opinion > on this..? > Well, for this issue, we had explained the roles of congestion window estimation in the last email. Some further discussions will come soon. _______________________________________________ Rohc mailing list Rohc@ietf.org https://www1.ietf.org/mailman/listinfo/rohc
- [rohc] Congestion window tracking in RoHC-TCP Per Synnergren (EPL)
- Re: [rohc] Congestion window tracking in RoHC-TCP West, Mark (ITN)
- RE: [rohc] Congestion window tracking in RoHC-TCP Lars-Erik Jonsson (EPL)
- RE: [rohc] Congestion window tracking in RoHC-TCP Qian Zhang
- Re: [rohc] Congestion window tracking in RoHC-TCP West, Mark (ITN)
- Re: [rohc] Congestion window tracking in RoHC-TCP Per Synnergren (EPL)
- Re: [rohc] Congestion window tracking in RoHC-TCP West, Mark (ITN)
- RE: [rohc] Congestion window tracking in RoHC-TCP Dr. Carsten Bormann