WLAN to cellular handover techniques for voice calls

A method, comprising:

• performing an IP multimedia subsystem (IMS) voice session over one or more wireless local area networks via a non-3GPP interworking function (N3IWF) or evolved packet data gateway (ePDG);
• storing information indicating that a first network using a first 3GPP cellular radio access technology (RAT) does not support voice communications for a user equipment (UE);
• and
• handing over the IMS voice session from the one or more wireless local area networks directly to a second network using a second 3GPP cellular RAT, based on the stored information and without handover of the IMS voice session to the first 3GPP cellular RAT.

An apparatus, comprising:

• a processor configured to cause a user equipment (UE) to:
• perform, over a wireless local area network, an IP multimedia subsystem (IMS) registration via a non-3GPP interworking function (N3IWF) or evolved packet data gateway (ePDG);
• establish connection over one or more of a first 3GPP network and a second 3GPP network;
• determine that the first 3GPP network:
• does not support voice communications for the apparatus;
• or
• supports only fallback to the second 3GPP network for voice communications;
• originate or receiving a voice call via the N3IWF or ePDG;
• disable a capability associated with the first 3GPP network based on one of:
• (a) IMS registration via the N3IWF or ePDG;
• or
• (b) originating or receiving a voice call via the N3IWF or ePDG;
• handover the voice call from the wireless local area network directly to the second 3GPP network using a second 3GPP cellular radio access technology (RAT) in response to disabling the capability associated with the first 3GPP network;
• and
• enable the capability associated with the first 3GPP network based on one of:
• (a) IMS deregistration via the N3IWF or ePDG;
• or
• (b) ending of the voice call.

A processor comprising circuitry configured to perform operations comprising:

• performing an IP multimedia subsystem (IMS) voice session over one or more wireless local area networks via a non-3GPP interworking function (N3IWF) or evolved packet data gateway (ePDG);
• storing information indicating that a first network using a first 3GPP cellular radio access technology (RAT) does not support voice communications for a user equipment (UE);
• and
• handing over the IMS voice session from the one or more wireless local area networks directly to a second network using a second 3GPP cellular RAT, based on the stored information and without handover of the IMS voice session to the first 3GPP cellular RAT.