> From: Tony Li <[email protected]> > Well, to me, central to the notion of the Internet architecture and > qmore specifically to a routing architecture is the notion of topology. > It would seem somewhat challenging to be able to describe topology > without being able to describe a graph.
I agree pretty much 100% with all you've said, but one minor caveat (and the credit for this observation goes to someone else, but I can't remember who, or what mailing list - sorry): using a graph as a model of the network connectivity (probably a more accurate term than 'topology', but I think we're stuck with the latter now) usually works very well, but... it is not necessarily the be-all and end-all. For some networks (e.g. wireless) it may not work so well. Graphs do have issues in other cases too, e.g. this one: http://mercury.lcs.mit.edu/~jnc/tech/abstraction_flame.html Having said that, I don't have what I consider a superior alternative, for the mathematical model of network connectivity, here in my hip-pocket, ready to offer. Like a like of things in routing, there are trade-offs: accuracy versus amount of information needed to describe a particular connectivity pattern is one, and for _most_ networks, using a graph to model the connectivity does really, really well on this. I don't know how difficult it would be to come up with a routing architecture that could support multiple models simultaneously (e.g. a graph for most of the network, but other stuff for local regions, e.g. perhaps something geographic for a wirless network, etc, etc). My intuition says it would probably be hard (impossible) to design an architecture where one could incrementally deploy new models in an interoperable way. But all that is pretty advanced - we're still a long way from an architecture which would allow even simpler stuff, like multiple path-selection algorithms with incremental deployment of new ones, local control of abstraction, etc. (I mean a long way in deployment terms - a vaguely plausible design was done a long time ago.) Noel _______________________________________________ rrg mailing list [email protected] http://www.irtf.org/mailman/listinfo/rrg
