Refer to RFC 1122, 18.104.22.168.
10 milliseconds to 500 milliseconds
Do not increase this value to more than 500 milliseconds.
Increase the value under the following circumstances:
Slow network links (less than 57.6 Kbps) with greater than 512 bytes maximum segment size (MSS)
The interval for receiving more than one TCP segment is short
For information, see tcp_local_dack_interval (Solaris 10 Releases).