2.2.3.7 MessageNumber

The <MessageNumber> element is the counter within the scope of the instance identifier for the current message. This MUST be generated at run time, and the MessageNumber MUST be incremented for each message. The MessageNumber of the first message sent within the scope of the current InstanceId SHOULD be "1". Note that the InstanceId and the use and increment of the same MessageNumber apply to other message types defined in [WS-Discovery] that the applications using the Discovery Protocol can send, not just the ProbeMatch message defined in the Discovery Protocol. The rules on initializing, processing, and incrementing the MessageNumber are specified in [WS-Discovery], Appendix I – Application Sequencing.