Can UE Mention APN as IMS during Initial Attach message

Question

1. Can UE Mentioned APN as "IMS" during Initial Attach message or it has to traverse through LTE Network?
2. While sending Rx message with out Gx session existing getting error (IP_CAN_SESSION_NOT_AVAILABLE), why is it so?
3. Framed-Ip-Address in Gx and Rx should be same ?

Answer 1

Yes UE can mention APN as IMS during the attach procedure. UE can attach to network by establishing the internet bearer or IMS bearer. In Gx interface, PCEF and PCRF exchange Bearer-Usage AVP within the CCR/CCA messages. Bearer-Usage AVP can contain two values i) General ii) IMS_SIGNALLING . Based on this value, PCRF assign the required QoS.
As per my knowledge, Framed-Ip-Address is the address allocated to UE.

Please check whether PCRF was involved in IP-CAN Session establishment or not.
Gx session should be in place before AF (Application function) initiates RAR message towards PCRF for an UE.

References:
3GPP 29214 and 29212 specifications.