[e2e] Agility of RTO Estimates, stability, vulneratibilites

[Craig Partridge]

I split out the more formal discussion.

In message <42E35AA7.60301 at web.de>, Detlef Bosau writes:

>The RTO used in TCP is a confidence interval for RTT.
>TCP _assumes_ (if implicitly) the existence of a reasonable RTO estimator.
>
>Is this correct?

Yes.

>
>Q2: What are other vulnerabilities and implicit assumptions?
>
>-Are there assumptions concerning the latency distribution?

I don't know that the question has been asked in quite this way in the
past.  As best I can answer it, I believe the assumption is the following:

    * there may be multiple round-trip paths in use at the same time
      for the same TCP connection.

    * for a particular path the following is true:

	+ there is a minimum latency (the base RTT) PLUS
	+ some distribution of added delay which is non-gaussian

>-Are there assumptions concerning the latency _stability_? What about 
>latency oscillations?

Yes.  A path is assumed to be stable only for some (undetermined but
non-negligible) period of time after which it may change and the
RTT may change by orders of magnitude.  It is possible to bounce between
two or more paths.

>Is this question stupid? If not: Is there existing work on this issue? 
>If so, I would appreciate any hint.

Not much was written down.  The literature mostly dates from a flurry of
work in the late 1980s.   If you want to pursue this formally, I think
the field is clear before you.

Craig