[e2e] common congestion controller for TCP connections

[Joe Touch]

Hari Balakrishnan wrote:
> Joe,
> 
> When we wrote our TCP (under Linux; non-BSD!) that decoupled congestion control 
> from it and only left the loss recovery in it, the end result was a 
> substantially simpler, easier-to-understand TCP and stack.  Modularity helps in 
> this case quite a bit.

I am not surprised that your rewriting Linux TCP, with the CM or not, 
would end up with a substantially simpler TCP and stack. That CM 
simplfied things is certainly useful.

> When you're dealing with something as complex as a TCP, I would be wary of 
> schemes that claim to be simpler because they only "play with TCB variables".  
> As we all know, even a "small" change in a TCP can have unintended, adverse 
> interactions and consequences.

Just as rewriting the whole of TCP's congestion management in an 
external module is a large change that can have unintended, adverse 
interactions and consequences. Not the least of which is needing to 
prove, a-priori, that this version of TCP is equivalent to Linux TCP 
under the conditions of a particular experiment.

If what is desired is to play with the particular variables being shared 
(which is, at least I think, the point of the proposed work), CM may 
have unintended artifacts that affect an implementation.

Joe