[e2e] YNT: A Question on the TCP handoff
Jon.Crowcroft at cl.cam.ac.uk
Sat Dec 10 10:17:43 PST 2005
there's two different causes for route change - one is link outage, and the other is mobile
- but in both, one could alleviate the impact on e2e tcp performance, and on existing
traffic on the links in the new route, as traffic is switched over from the old route,
by modifiying the routing algorithm.
if the routing algorithm computes routes that are incremental steps different from the old
route (even include the routers either side of the old routes link that brok,e or access
point that one is switching away from in the mobiel handover case) and then slowly migrated
the route to the new "shortest path", then the impact would be massively reduces as the RTT
would change in a small number of steps, rather than one big step,
and the "bottleneck capacity" would potentially
change more smoothly too.
given interdomain routing isnt SPF anyway, i dont see why there can be anyobjection to this
- also, it doesn't need any tcp state in the routers to do it - its just a change to the
way we get from the result of one dijkstra or one BGP outcome, to another -its like a
generalised version of crankback, then crankforward, but with live traffic
an added benefit os such a routing algorithm would be that under churn, or heavy
flapping, the route performance as perceived by end2end users would be relatively stable.
what would such an algorithm look like? well, its a bit like the opposite of a link
disjoint load balancing routing algorithm - i leave it as an excercise for the reader to
come up with a modification to OSPF and BGP to achieve such a goal as there isn't space
between these two pixels to write it down......
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