On 10/28/07, Gerrit Renker <gerrit@xxxxxxxxxxxxxx> wrote: > [CCID2]: Deadlock and spurious timeouts when Ack Ratio > cwnd > > This patch removes a bug in the current code. I agree with Andrea's comment > that there is a problem here but the way it is treated does not fix it. > > The problem is that whenever Ack Ratio > cwnd, starvation/deadlock occurs: > * the receiver will not send an Ack until (Ack Ratio - cwnd) data packets > have arrived; > * the sender will not send any data packet before the receipt of an Ack > advances the send window. > The only way that the connection then progresses was via RTO timeout. In one > extreme case (bulk transfer), it was observed that this happened for every single > packet; i.e. hundreds of packets, each a RTO timeout of 1..3 seconds apart: > a transfer which normally would take a fraction of a second thus grew to > several minutes. > > The solution taken by this approach is to observe the relation > > "Ack Ratio <= cwnd" > > by using the constraint (1) from RFC 4341, 6.1.2; i.e. set > > Ack Ratio = ceil(cwnd / 2) > > and update it whenever either Ack Ratio or cwnd change. This ensures that > the deadlock problem can not arise. > > Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx> Acked-by: Ian McDonald <ian.mcdonald@xxxxxxxxxxx> - To unsubscribe from this list: send the line "unsubscribe dccp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
