Re: [TERNLI] Notes from tonight's ad hoc
Gorry Fairhurst <gorry@erg.abdn.ac.uk> Mon, 31 July 2006 18:31 UTC
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Date: Mon, 31 Jul 2006 15:55:20 +0100
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
Organization: University of Aberdeen, UK
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To: Lars Eggert <lars.eggert@netlab.nec.de>
Subject: Re: [TERNLI] Notes from tonight's ad hoc
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Cc: ternli@ietf.org, Michael Welzl <Michael.Welzl@uibk.ac.at>, Joe Touch <touch@ISI.EDU>
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Lars Eggert wrote: > Hi, > > On Jul 29, 2006, at 3:23, Joe Touch wrote: > >> Right. I like the idea of "only give info that you think the next layer >> can use", but not "tell the next layer what you want it to do". Also, >> the information passed ought to be something that makes sense in the >> context of the next layer, e.g., tell the network layer about a path >> property, not about a link technology, etc. > > > this is probably one of the most precise - and concise - descriptions > of the idea we've been kicking around I've see so far. > > Also, we've so far mostly thought about the network/transport interface > and what additional information could be passed across it that would > allow some new response mechanisms at the transport layer to improve > performance. However, the principle of extending interfaces in this way > - as you've summarized above - can also be applied to the link/network > and transport/application interface. The link/network part is to some > degree looked at by mobopts (although maybe not following the approach > identified above). I'm unaware of extensions to the transport/app > interface. > > Finally, this discussion has mostly talked about moving information of > a certain kind up the stack in a certain way. Someone (Mark Handley?) > had pointed out that the reverse direction may also be important to > look at. Your text above can be read to apply to both directions, which > is nice. > > Lars I'm still not yet convinced we understand exactly what the TRANSPORT can usefully utilise, and which it can rely upon to make safe decisions. * One issue that came up time and again in the previuous BoFs - how does the tranport entity KNOW the signal is from a node on the path, and how much do you wish to continue the idea of "fate-sharing" and "alternate paths" - in which it's hard to know if link characteristics really impact flows. * If you know that some of the packets in the flow have been through the device, do you trust it? There's DOS opportunities here, and also issues of trust between ISPs and Core providers. * Finally, in the TrigTran BoFs, I also recall some discussion of time-scales, what seems like a "timely" event at the physical layer, may not be of interest to the transport layer (working on a timescale of several Path RTTs). I and others have said these sorts of things several times (sorry), and it would be really good to capture exactly which signals are trust-worthy and useful to a transport entity. In the other direction: What are the things the transport enities could tell the link/phy? and how will it know to use these? WE already have QoS and QS/XCP type signals, what are the additional features desired? I think if we understand the usefulness, we can make progress. One example of "something that changed" is advice that the link RTT is large (or has just become large) could be useful. For this, it's wise to make transport protocols that don't rely on exact timing (which is good practice and we're doing this), so simply bumping up the stored RTT seems plausible (and then letting the transport reprobe to confirm this). I think Mark (?) queried whether we need to be exact about what changed has... could it be that any path change would sensibly lead to the same sort of re-probe to confirm RTT, MTU, etc? Gorry
- [TERNLI] Notes from tonight's ad hoc Spencer Dawkins
- Re: [TERNLI] Notes from tonight's ad hoc Wesley Eddy
- Re: [TERNLI] Notes from tonight's ad hoc Spencer Dawkins
- Re: [TERNLI] Notes from tonight's ad hoc Mark Allman
- RE: [TERNLI] Notes from tonight's ad hoc Kevin Fall
- Re: [TERNLI] Notes from tonight's ad hoc Wesley Eddy
- Re: [TERNLI] Notes from tonight's ad hoc Mark Allman
- Re: [TERNLI] Notes from tonight's ad hoc Michael Welzl
- RE: [TERNLI] Notes from tonight's ad hoc Kevin Fall
- RE: [TERNLI] Notes from tonight's ad hoc Michael Welzl
- Re: [TERNLI] Notes from tonight's ad hoc Mark Allman
- Re: [TERNLI] Notes from tonight's ad hoc Wesley Eddy
- Re: [TERNLI] Notes from tonight's ad hoc Michael Welzl
- Re: [TERNLI] Notes from tonight's ad hoc Joe Touch
- Re: [TERNLI] Notes from tonight's ad hoc Mark Allman
- Re: [TERNLI] Notes from tonight's ad hoc Joe Touch
- Re: [TERNLI] Notes from tonight's ad hoc Lars Eggert
- Re: [TERNLI] Notes from tonight's ad hoc Gorry Fairhurst
- Re: [TERNLI] Notes from tonight's ad hoc Spencer Dawkins
- Re: [TERNLI] Notes from tonight's ad hoc Aaron Falk
- Re: [TERNLI] Notes from tonight's ad hoc Aaron Falk
- Re: [TERNLI] Notes from tonight's ad hoc Joe Touch
- Re: [TERNLI] Notes from tonight's ad hoc Joe Touch
- Re: [TERNLI] Notes from tonight's ad hoc Gorry Fairhurst
- Re: [TERNLI] Notes from tonight's ad hoc Aaron Falk
- Re: [TERNLI] Notes from tonight's ad hoc Bob Briscoe
- Re: [TERNLI] Notes from tonight's ad hoc Lars Eggert
- Re: [TERNLI] Notes from tonight's ad hoc Bob Briscoe
- Re: [TERNLI] Notes from tonight's ad hoc Joe Touch