3.2.5.15.2 Sending the Initiate Multitransport Response PDU
The structure and fields of the Initiate Multitransport Response PDU are described in section 2.2.15.2, and the PDU MUST be initialized according to this specification. The embedded initiator field of the mcsSDrq field MUST be set to the User Channel ID held in the User Channel ID store (section 3.2.1.4), while the embedded channelId field MUST be set to the MCS message channel ID held in the Message Channel ID store (section 3.2.1.3). Furthermore, the embedded flags field of the securityHeader MUST contain the SEC_TRANSPORT_RSP (0x0004) flag (section 2.2.8.1.1.2.1).
This Initiate Multitransport Response PDU indicates to the server that a sideband initiation request succeeded or failed. If the hrResponse field indicates a failure, the client MUST NOT attempt to create a sideband channel after sending this PDU.