公开(公告)号：EP3780757A1

公开(公告)日：2021-02-17

申请号：EP20000297.0

申请日：2020-08-17

Applicant: Apple Inc.

Inventor： Venkataraman, Vijay ,  Kiss, Krisztian ,  Tiwari, Shashikant ,  Nimmala, Srinivasan ,  Kavuri, Lakshmi N. ,  Babu, Shivani Suresh ,  Kodali, Sree Ram ,  Prakasam, Sridhar ,  Schweizer, Stephen C. ,  ZHU, Yifan

IPC: H04W48/18 ,  H04L29/06 ,  H04W80/10 ,  H04W88/06

Abstract: Apparatuses, systems, and methods for a user equipment device (UE) to perform methods for EPS fallback when initiating a voice call while camped on a 5G cell. The UE may camp on a 5G network by performing an IMS registration procedure/IMS SIP invite procedure with an IMS. The UE may initiate a voice call and determine that the voice call cannot be established over the 5G NR network. In response, the UE may perform a TAU procedure or an attachment procedure with a cell of a 4G network. The IMS may be transferred to the 4G network during TAU/attachment procedure. The UE may, in response to determining that it is barred from the 4G network, transition back to the 5G network and transmit, to the 5G NR network, a SIP cancel request to allow a context associated with the UE to be cleared from the IMS.