188.8.131.52 Delayed ACK Timer
This timer fires on the receiver at the delayed ACK time-out after the receipt of a Source Packet if no acknowledgment (section 184.108.40.206) has been scheduled for that Source Packet. The delayed ACK time-out depends on the negotiated protocol version (section 220.127.116.11) as follows:
RDPUDP_PROTOCOL_VERSION_1: the delayed ACK time-out is 200 ms.
RDPUDP_PROTOCOL_VERSION_2: the delayed ACK time-out is 50 ms or half the RTT, whichever is longer, up to a maximum of 200 ms.
Once the timer is fired, an acknowledgment for that Source Packet MUST be generated and sent. The receiver MUST set the RDPUDP_FLAG_ACKDELAYED flag in the uFlags field of the RDPUDP_FEC_HEADER structure.
This timer is needed only when the receiver generates one cumulative acknowledgment for a number of Source Packets, as specified in section 18.104.22.168. In this case, this timer indicates that there is at least one Source Packet at the receiver for which an acknowledgment has not been generated and sent.