3.1.5.1 Constructing Handshake PDU
The Handshake PDU is constructed during initialization of the remote applications integrated locally (RAIL) virtual channel. The buildNumber field SHOULD be initialized to the build or version of the sending party. This PDU (or alternatively the HandshakeEx PDU (section 2.2.2.2.3) if the sending party is the server) MUST be sent before any other PDU on the virtual channel.