DAT - If set, data is contained in the packet, and the sequence number is valid. The packet, even if zero length, must be delivered. This bit may be combined with the DAT bit to piggyback an acknowledgment on a data packet. The pvmd is closing down the connection. The state of a connection to another pvmd is kept in its host table entry.
Figure shows the host send and outstanding-packet queues.
Packets are appended to this queue by the routing code, described in Section . The protocol allows multiple outstanding packets to improve performance over high-latency networks, so two more queues are required. The difference in time between sending a packet and getting the acknowledgement is used to estimate the round-trip time to the foreign host. Each update is filtered into the estimate according to the formula . Each packet has a retry timer and count, and each is resent until acknowledged by the foreign pvmd.