22.214.171.124.1.1 Processing a Server Capabilities Request Message
The structure and fields of the Server Capabilities Request message are defined in section 126.96.36.199.1.
This MUST be the first message that a client receives on each connection within the PNP Device I/O Subprotocol. The client inspects the version field. For example, if the client receives a version of 6 or later (future versions of the protocol MAY send a later version, although current ones do not) from the packet described in section 188.8.131.52.1, the client MAY send packets that describe custom events, as described in section 184.108.40.206.10. However, if the version is earlier than 6, the client MUST NOT send packets that describe custom events.
The client MUST reply with its own version by sending a Client Capabilities Reply message.