[e2e] Why are missing ACKs not considered as indicator for congestion?

[Saverio Mascolo]

On 2/5/07, Douglas Leith <doug.leith at nuim.ie> wrote:
  Perhaps I can add my own question to this.   The discussion so far
  has mostly centered on whether its possible to detect ack losses.
  But say we could measure these ack congestion/losses - what would the
  right thing be to do ?  Should we  treat loss of any packet (ack or
  data) as congestion, or just consider loss of data packets as being
  meangingful ?

  This isn't  as abstract a question as it might at first seem.  Most
  delay-based algorithms use two-way delay and so react to queueing of
  acks as well as data packets.  That is, unlike loss based algorithms
  they *do* treat ack and data packets in similar ways for congestion
  control purposes.  Is this a good thing or not ? Doug     


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of course it is not good. we had a paper on performance evaluation of NewReno, Vegas and TCP Westwood+ on ACM CCR 2004 showing that reverse traffic (i.e. ack queuing) shut down forward vegas traffic. the effect of reverse traffic was also shown for Fast TCP in a paper we had at pfldnet 06.
to conclude, in case of delay based control you should measure forward delay, rrt is not enough.

saverio
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