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4/8/2010
As specified in RFC 1122, TCP uses delayed acknowledgments (ACKs) to reduce the number of packets sent on the media. The Microsoft stack takes a common approach to implementing delayed ACKs. As data is received by TCP on a given connection, it only sends an acknowledgment back if one of the following conditions is met:
- No ACK was sent for the previous segment received.
- A segment is received, but no other segment arrives within 200
milliseconds for that connection.
In summary, normally an ACK is sent for every other TCP segment received on a connection, unless the delayed ACK timer (200 milliseconds) expires. The delayed ACK timer can be adjusted through the TcpDelAckTicksregistry entry.