Yes, Bakul, keeping a central RTT cache per destination is a good idea. Most good stacks use it already. I think it was recommended in Host Requirements circa 1989. Keeping a per destination cache of Path RTT, Path MTU, and a Quality measurement was required in my initial IPng Neighbor Discovery design several years ago, before that was destroyed in the rewrite by committee.

From: Bakul Shah <bakul@torrentnet.com> [Thinking aloud here...] Perhaps a part of the TCP congestion avoidance algorithm can be factored out in some sort of a `traffic central' module that tries to give you the best bandwidth/packet loss estimate it has for a given route provided you keep it updated with what you learn (i.e. TCP tells it when a packet is lost etc). A new TCP connection can then immediately start off with a bigger window (and won't open the window too wide too quickly). Multiple connections between two hosts can avoid what would be largely redundant estimate computation. Even a UDP app. can try to benefit from this (such as for communication where bounded delay is more critical than packet loss). Other `traffic conditions' input can also be fed into this module [perhaps as part of some future routing protocol]. Combining this `quality' of a route aspect into routing protocols may make sense in the long run....

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