3PCC (Third Party Call Control) can be used by Lotus Sametime Unified Telephony applications to generate and manipulate calls. These 3PCC generated calls may be calls routed via a SIP Service Provider.
In order to support 3PCC the SIP Service Provider must support the procedures described in RFC3725. In particular, the Service Provider must be able to support at least Flow I of RFC 3725 (in fact, accept a SIP INVITE request that does not include an SDP offer and be able to support the SDP offer/answer exchange via the SIP 200 OK and ACK messages).
Parent topic: SIP Trunking overview