Re: [homenet] Updates to Homenet Architecture Principles doc
Juliusz Chroboczek <jch@pps.univ-paris-diderot.fr> Thu, 12 June 2014 14:34 UTC
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Date: Thu, 12 Jun 2014 16:34:36 +0200
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From: Juliusz Chroboczek <jch@pps.univ-paris-diderot.fr>
To: Ted Lemon <mellon@fugue.com>
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Cc: "homenet@ietf.org Group" <homenet@ietf.org>
Subject: Re: [homenet] Updates to Homenet Architecture Principles doc
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>> This sounds _way_ too specific to me. > If you are just going to laugh, Laugh with us, Ted -- it /is/ rather funny. (I especially liked the "linear sum" touch. What's a non-linear sum?) > This statement should be inclusive of whatever routing protocols the > working group is inclined to consider, I'll do my best. There are at least four issues at hand. 1. Not all routing protocols choose the lowest-metric route -- some protocols include in their route selection criteria data that are not encoded in the metric. Examples are BGP flap avoidance, or the hysteresis algorithm used by Babel. One might argue that this is also the case of multi-area OSPF (although it is not usually expressed in that manner). For BGP and OSPF, you probably know more about the subject than I do. For Babel, see Section 3.6 of RFC 6126 and Section III.E of http://arxiv.org/pdf/1403.3488 (As far as I know, there is currently no theoretical understanding of this kind of techniques. As far as I've been able to work out, neither Sobrinho's routing algebras nor Griffin's semigroups are able to account for them.) The Arch document MUST NOT specify what kind of data the route selection algorithm is allowed to take as input. 2. Many protocols don't compute metrics as a "linear sum" of the link costs; as a matter of fact, in many protocols the metric is not a mere integer, but an element of a richer algebra. This is obviously the case of BGP (see Griffin and Sobrinho, SIGCOMM 2005), but also of Babel, which, when run over a radio link layer with interference avoidance enabled, carries a pair of an integer and (roughly speaking) a set of interfering radio frequencies. The Arch document MUST NOT specify the structure of the metric algebra. It SHOULD NOT even imply that the metric being used is modelisable as a routing algebra. 3. Finding a satisfactory and implementable metric for radio link layers is very much an open research problem. Many routing protocols just punt and expect the link layer to work like an Ethernet, which gets you horrible performance in rich layer 3 topologies. Some mesh routing protocols estimate unicast link rate and multicast packet loss and combine the two using magic, which tends to choose unusable routes in some cases. There has been a lot of noise around cross-layer techniques for the last 10 years or so, but I don't know of a production-quality implementation. (Yeah, I know, I should stop complaining and try my hand at it.) Please do not underestimate the importance of this point for Homenet -- how many wired and how many wireless links do you expect there to be in a typical home ten years from now? The Arch document MUST NOT specify what kind of data the metric computation algorithm is allowed to take as input. 4. There exist routing protocols that don't use the notion of a metric at all. We metric-based people like to jestingly call them "longest-path routing" algorithms, however we're still keeping an eye open to see if anything useful comes out from that line of research. The Arch document SHOULD NOT even imply that a metric is being used. Hope this helps, -- Juliusz
- [homenet] Updates to Homenet Architecture Princip… Ray Bellis
- Re: [homenet] Updates to Homenet Architecture Pri… Markus Stenberg
- [homenet] Updates to Homenet Architecture Princip… Ray Bellis
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Markus Stenberg
- Re: [homenet] Updates to Homenet Architecture Pri… Mark Townsley
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Townsley.net
- Re: [homenet] Updates to Homenet Architecture Pri… Acee Lindem
- Re: [homenet] Updates to Homenet Architecture Pri… Townsley.net
- Re: [homenet] Updates to Homenet Architecture Pri… Michael Thomas
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Michael Thomas
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Acee Lindem
- Re: [homenet] Updates to Homenet Architecture Pri… Ray Hunter
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Michael Richardson
- Re: [homenet] Updates to Homenet Architecture Pri… Michael Richardson
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Brian E Carpenter
- Re: [homenet] Updates to Homenet Architecture Pri… Lorenzo Colitti
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Markus Stenberg
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Lorenzo Colitti
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Lorenzo Colitti
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Lorenzo Colitti
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Tim Chown
- Re: [homenet] Updates to Homenet Architecture Pri… Mark Townsley
- Re: [homenet] Updates to Homenet Architecture Pri… Tim Chown
- Re: [homenet] Updates to Homenet Architecture Pri… Tim Chown
- Re: [homenet] Updates to Homenet Architecture Pri… Mark Townsley
- Re: [homenet] Updates to Homenet Architecture Pri… Tim Chown
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Mark Townsley
- Re: [homenet] Updates to Homenet Architecture Pri… Brian E Carpenter
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Mark Townsley
- Re: [homenet] Updates to Homenet Architecture Pri… Ray Hunter
- Re: [homenet] Updates to Homenet Architecture Pri… Ted Lemon
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Ray Hunter
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Ray Hunter
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Ray Hunter
- Re: [homenet] Updates to Homenet Architecture Pri… Juliusz Chroboczek
- Re: [homenet] Updates to Homenet Architecture Pri… Acee Lindem
- Re: [homenet] Updates to Homenet Architecture Pri… Alexandru Petrescu
- Re: [homenet] Updates to Homenet Architecture Pri… Alexandru Petrescu
- Re: [homenet] Updates to Homenet Architecture Pri… Alexandru Petrescu
- Re: [homenet] Updates to Homenet Architecture Pri… Gert Doering
- Re: [homenet] Updates to Homenet Architecture Pri… Alexandru Petrescu
- Re: [homenet] Updates to Homenet Architecture Pri… Tim Chown
- Re: [homenet] Updates to Homenet Architecture Pri… ietfdbh
- Re: [homenet] Updates to Homenet Architecture Pri… joel jaeggli
- Re: [homenet] Updates to Homenet Architecture Pri… Tim Chown
- Re: [homenet] Updates to Homenet Architecture Pri… Ray Hunter
- Re: [homenet] list of questions on routing sectio… Alexandru Petrescu
- Re: [homenet] list of questions on routing section Alexandru Petrescu