3.1.4.18 Large Messages
When a higher-level entity (game) requests that the DirectPlay client send a message that is larger than the maximum transmission unit (MTU) size supported by the transport, the sending client MUST split the message into smaller fragments that will fit. Each fragment MUST then be transmitted using a DPSP_MSG_PACKET (section 2.2.39) header if the message is not reliable, or a DPSP_MSG_PACKET2_DATA (section 2.2.41) header if the message is reliable. If it is not reliable, the DPSP_MSG_PACKET messages SHOULD be transmitted without waiting for an acknowledgement. If it is not reliable, the sender MUST only send the first DPSP_MSG_PACKET2_DATA message and MUST start the Packetize Timer to retry the fragment if necessary. Future reliable fragments MUST NOT be sent until this fragment is acknowledged as specified in sections 3.1.5.28 and 3.1.5.29.