The MCS Channel Join Request PDU is an RDP Connection Sequence PDU sent from client to server during the Channel Connection phase (see section 1.3.1.1). It is sent after receiving the MCS Attach User Confirm PDU (section 2.2.1.7). The client uses the MCS Channel Join Request PDU to join the user channel obtained from the Attach User Confirm PDU, the I/O channel and all of the static virtual channels obtained from the Server Network Data structure (section 2.2.1.4.4).