1.3.2.1.1 Connection Setup and Authentication Phase
The connection setup and authentication phase only involves the exchange of HTTP header information and consists of three operations:
Create OUT channel: An HTTP 1.1 connection is established. If the RDG server and client both support the WebSocket protocol ([RFC6455]), then this connection is used for duplex communication between the RDG client and server; otherwise, this connection is used only for outbound communication from the RDG server.<5> WebSocket support is negotiated using the Opening Handshake as specified in [RFC6455] section 1.3.
Create IN channel: A second HTTP 1.1 connection is established for inbound communication to the RDG server if the RDG server and client don't support the WebSocket protocol. In this case, the OUT channel is used only for outbound communication.
Authenticate user.

Figure 5: Message sequence between RDG client and RDG server during connection setup and authentication phase