[Tmrg] Now, where were we...?
lachlan.andrew at gmail.com (Lachlan Andrew) Thu, 19 November 2009 00:47 UTC
From: "lachlan.andrew at gmail.com"
Date: Thu, 19 Nov 2009 11:47:14 +1100
Subject: [Tmrg] Now, where were we...?
Message-ID: <aa7d2c6d0911181647i755ed6eft9dbe3168d38019b3@mail.gmail.com>
Greetings all, Things have been rather quiet on this list since Sally's retirement, and I'd like to get things moving again (after Aaron's gentle prompting :) Just as a stock-take, could people please indicate whether they consider themselves A: part of the TMRG B: subscribed to this list to follow "what they in the TMRG are doing" Since this WG was chartered as "mailing-list only", everyone on the list is really in group A, whether they know it or not. For those who prefer publishing papers than writing Internet Drafts, remember that the licence for an ID allows "derivative works", so you can still publish your models/evaluation/... Like the ArXiv, the ID process is a good way to place a stamp on your ideas and get feedback before publishing. What important open issues issues are there in transport modelling? (Rather than having an "open issues" draft like ICCRG is doing, let's start with a discussion here.) To get the ball rolling, here are some issues (mostly courtesy of Doug Leith): 1. How can we model "loss synchronisation" between flows sharing a congested link? Theoretical models typically assume either that the per-packet loss probability is equal for all flows (no synchronisation) or that all flows lose a packet whenever one flow does (perfect synchronisation). The truth is somewhere in between, but where? How does it depend on the behaviour of the transport algorithms? (e.g., H-TCP induces more synchronisation than Reno. CUBIC can induce either more or less, depending on how its fast-convergence mode behaves.) 2. How reliable are implicit congestion indicators? The prevailing wisdom in the IETF seems to be that "ECN=loss = congestion, delay = noise, nothing else is useful for congestion control". What criteria would "delay" have to satisfy in order to be a useful indicator of congestion? Should we listen to the average delay, the frequency with which delay exceeds a threshold, or the jitter? More importantly, are there other ways the network might be telling us things? For example, does packet reordering tell us anything? (I believe that Van Jacobson's key insight was not "loss indicates congestion", but that we should "listen to the network calling for help", however it does that.) 3. Most internet users are now home users with dedicated bottlenecks, rather than institutional users. Should we reconsider whether artefacts such as phase effects deserve a place in our models? Recently some people here at Swinburne noticed a similar effect occurring with a single CUBIC flow on a "clean" network. Are these artefacts or important phenomena? 4. What role should highly-idealised models play? Are there generic ways to include important phenomena like jitter and loss synchronisation into mathematical models of congestion control, or is that too naive? 5. What aspects of transport protocols need to be modelled other than their congestion control mechanisms (for which we have the ICCRG...)? For example, are there "correctness" issues (deadlock avoidance etc) with multi-path and multi-endpoint transport protocols? Does this list reach the right community to address those issues? Cheers, Lachlan -- Lachlan Andrew Centre for Advanced Internet Architectures (CAIA) Swinburne University of Technology, Melbourne, Australia <http://caia.swin.edu.au/cv/landrew> <http://netlab.caltech.edu/lachlan> Ph +61 3 9214 4837
- [Tmrg] Now, where were we...? Lachlan Andrew
- [Tmrg] Now, where were we...? Larry Dunn
- [Tmrg] Now, where were we...? Michael Welzl
- [Tmrg] Now, where were we...? Stefan Hirschmann
- [Tmrg] Now, where were we...? Michael Welzl
- [Tmrg] Now, where were we...? Lachlan Andrew
- [Tmrg] Now, where were we...? Damon Wischik
- [Tmrg] Now, where were we...? Lachlan Andrew
- [Tmrg] Now, where were we...? John Heffner
- [Tmrg] Now, where were we...? Lachlan Andrew
- [Tmrg] Now, where were we...? Michael Welzl
- [Tmrg] Now, where were we...? Lachlan Andrew