3.1.5.5 Sequencing of PDUs on the Multitransport Connection

The Remote Desktop Protocol: Multitransport Extension MUST begin with the RDP_TUNNEL_CREATEREQUEST PDU (section 2.2.2.1), which is sent from the client to the server. The client MUST NOT send any data to the server until it receives the RDP_TUNNEL_CREATERESPONSE_PDU (section 2.2.2.2) with a successful HRESULT code. The server MUST NOT send any data until it has received the RDP_TUNNEL_CREATEREQUEST PDU, processed it, and sent an RDP_TUNNEL_CREATERESPONSE PDU with a successful HRESULT code to the client.