BlackBerry Limited
Preserving Emergency Call During Failure to Transfer Subsequent to Registration with the Target Network

Abstract:

A method in a user equipment (UE) for transferring an ongoing connection or ongoing session via a first network includes transmitting a first registration request message to a second network of a first public land mobile network (PLMN); transmitting a first connectivity request message to the second network, the first connectivity request message includes an indication that connectivity belongs to the ongoing connection or the ongoing session; receiving, in response to the first connectivity request message, a message comprising a cause code from the second network; transmitting, in response to receiving the message comprising the cause code, a second registration request message to a third network of a second PLMN, the first PLMN and the second PLMN are different; and transmitting a second connectivity request message to the third network, the second connectivity request message includes the indication that the connectivity belongs to the ongoing connection or the ongoing session.