Voice call continuity allows users to move voice calls between the Circuit-Switched (CS) domain and the Multimedia Domain (MMD), connected through different Internet Protocol - Connectivity Access Networks (IPCANs) (e.g., WLAN, HRPD, E-UTRAN). This document defines an inter-technology Domain Transfer (DT) call model which supports procedures that allow a mobile subscriber to perform DT for the following cases:

– from a multimedia session with a voice component to a 1x CS voice session, and,

– for the case where the UE is equipped with dual radios (e.g., WLAN), from a 1x CS voice session to a multimedia session with a voice component.

It is the goal of this specification to allow the core network to know as precisely as possible the current accessibility of the User Equipment (UE) and to deliver services efficiently across the appropriate access network while minimizing the impact on the legacy systems.

The UEs in this specification include two kinds - one is single radio, dual mode handset (e.g., HRPD/1x), and the other is dual radio, dual mode handset (e.g., WLAN/1x). Single radio handsets are assumed to be incapable of simultaneous full-duplex radio communications with both a packet radio access network and a 1x radio access network, i.e., they have only one radio transmitter and may have one or two radio receivers. Dual radio handsets are assumed to be capable of being in simultaneous full-duplex communication with both a packet data access network and a 1x radio access network, i.e., they have two radio transmitters and two radio receivers.

Supplementary services and supplementary services continuity e.g., Call Waiting, Call Transfer, 3WC, Call Hold) are outside the scope of this document.

The Stage 2 of this document specifies the interactions and signaling flows between a new functional entity in the MMD network called the VCC Application Server (VCC AS) and the:

• Serving-Call/Session Control Function (S-CSCF) 􀂃 Home Location Register (HLR)

• Home Subscriber Server (HSS) 􀂃 Single Radio Terminal 􀂃 Dual Radio Terminal

• Mobile Switching Center (MSC)

• Media Gateway Control Function (MGCF)

The Stage 3 specification in this document provides the protocol details for voice call continuity between the MMD based on the Session Initiation Protocol (SIP) and the Session Description Protocol (SDP) and the 3GPP2 CS domain which uses MAP and ISUP.

This document makes no VCC specific enhancements to SIP, SIP events or SDP, beyond those specified in [MMD Part-4].

This document is applicable to UEs, AS and MGCF providing voice call continuity capabilities.