ICS 156: Networking Lab

4.3.4 Group and Delayed ACKs

nGroup ACKs: TCP will use group ACKs, also referred to as delayed ACKs. in otherwords, it will not ACK each received segment, it will wait for a short while (differs on each system, 200msecs for WANs, 20msec for LANs) and then ACK all segments (max. 2 segments) that it has received so far.

nIt does that so that: 1) it can do group ACKing which is more efficient, and 2) it hopes to be able to piggyback an ACK on data going in the reverse direction. If there is data in the buffer that needs to be sent, it will not do a delayed ACK. Only uses delayed ACK if send buffer is empty.