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

Detlef Bosau detlef.bosau at web.de
Mon Jan 29 12:48:47 PST 2007

My apologies for this question, perhaps it´s simple:

In TCP, lost / dropped packets are recognised as congestion indicator.
We don´t do so with missing ACKs.

Consider the following net:

     (downstream:)  T T T T T T T T T
Sender                                                           Receiver
     (upstream: )      AAAAAAAAAA     

Then the flow occupies the cumulated capacity of T(CP packets) and A(CK 

If CWND grows too large (by probing) and the available path capacity is 
exceeded, packet drop occurs.
If a TCP packet is dropped, this is reckognized as congestion 
indication. Shouldn´t be a dropped ACK packet seen as congestion 
indication as well?

Perhaps, this question is a bit stupid, but I don´t see the clue here at 
the moment. Perhaps, someone could help me please?



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