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3.10.4.1.1 Constructing an Outgoing SIP INVITE Request

Unless otherwise specified in the following section, the rules for constructing and sending an INVITE request are as specified in [RFC3261] section 13.2.1.

When the MCU receives an addUser dial-out request, it SHOULD initiate a signaling/media handshake with that user. The outgoing INVITE SHOULD be constructed using the following rules:

  • The URI in the SIP From header field MUST be set to the MCU-Conference-URI.

  • The URI in the SIP To header field SHOULD be set to the SIP URI specified in the entity attribute of the user element of the dial-out request.

  • The SIP Request-URI header field SHOULD be set as follows:

    • If the refer-to-uri attribute is supplied in the addUser dial-out request, it SHOULD be used to populate the SIP Request-URI header field.

    • If the endpoint-uri attribute is supplied in the addUser dial-out request, it SHOULD be used to populate the SIP Request-URI header field, provided that refer-to-uri is empty.

    • Otherwise, the SIP Request-Uri header field SHOULD be set to the URI in the To header field.

  • If the refer-to-uri attribute is specified, the MCU SHOULD parse this attribute, treating it as a SIP URI. It SHOULD extract all of the headers present and add them to the outgoing request, as defined in [RFC3261] section 19.

Extensions can define additional rules for session establishment between the MCU and the client.