[e2e] YNT: A Question on the TCP handoff/incremental route change

Jon Crowcroft Jon.Crowcroft at cl.cam.ac.uk
Sun Dec 11 05:39:11 PST 2005

increasing resolution so we can read between the pixels:

so the idea i was getting at was to do with the way both 
distance/path vector, and link state algorithms choose one route,
then, when a better route is discovered, switch abruptly to it.
To mitigate the effect (not to get rid of it completely, but to reduce
the size of one potential step function in rtt and bottleneck capacity
to a set of smaller changes), one can think of routing as a process of
recursive re-routing - the idea is quite simple - 

a current route gets from A to B. There is an outage, or else a new
route appears because of the end of an outage (or the introduction of a
new link, but lets leave that for now as its occasional)

so we can think of the routers either side of the outage and see if
there are routes from any router on the A-B path to the routers either
side of an old outage, or if its a new outage on A-B, from the routers
either side of the broken link (yes, and router:), to a better route.
How to do this in a distributed way without incurring some huge
overhead compared to normal link state?

well, lets assume ISPs aren't mad, and that a lot of links that are
avaialble for alternate routes are actually part of some planned
redundent capacity/topology, rather than accidental (I know this is
contraversal, as most papers on multipath routing seem to assume that
we consier all links in the world, but thats researchers for you -
most network providers don't work that way).

so then we actually cosider the problem _inside out_ - start as
reaching points either side of potential and actual outages, and
create a set of routes - how will that work? consider hierarchical
OSPF - and you are just laberling routers at each end of outages
as in the same level hierarchy, and links further on as the next level
of the hierarchy (can do similar for BGP). how to _stage_ the handover ?
ok - so we need to cascade the timers for the route update in each
level of the hierarchy. How to do that? that's where control theory
comes in, maybe although I was thinking of using a process algebra
like stochastic pi calculus myself.


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