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[lwip-devel] [task #14128] Appropriate byte counting/stretch ACK support

From: Joel Cunningham
Subject: [lwip-devel] [task #14128] Appropriate byte counting/stretch ACK support
Date: Fri, 3 Mar 2017 13:25:57 -0500 (EST)
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/602.4.8 (KHTML, like Gecko) Version/10.0.3 Safari/602.4.8

Follow-up Comment #5, task #14128 (project lwip):

Thanks for the heads up Ambroz.  RFC 5681 references RFC 3465 in "section 3.1.
 Slow Start and Congestion Avoidance".  I believe LwIP implements correctly
most of slow start/congestion avoidance/fast recovery, but I haven't done a
full audit.  I've just noticed the issue with cwnd being susceptible to ACK
division and performing sub-optimal when stretch ACKs are used (common case is
delayed ACKs)

RFC 5681 appears to only recommend updating cwnd according to cwnd += min (N,
SMSS), though it acknowledges that RFC 3465 allows increasing by more.  This
covers the ACK division security issue, but not compensating from delayed

I don't see any particular issue with compensating for a 2 * MSS stretch ACK,
but welcome other thoughts on the matter


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