In which scenario, network triggers E-RAB setup procedure to establish multiple bearers for an UE?

Question

As per 36.413, E-RAB setup request message has defined a list of E-RAB to be setup items. As per my understanding, this message is triggered only when a new PDN connection is established or a dedicated bearer for an UE.

Can someone please help to realize a scenario, in which network triggers this message for a list of radio bearers.

Comments

You are right, network triggered E-RAB is nothing but the PCRF triggered Bearer, For Ex. A VoLTE call required a Default n Dedicated Bearer, where dedicated is triggered by network(PCRF).

Answer 1

Use case scenario where Network Triggered ERAB setups are made:

Consider a case of VoLTE Video call scenario in which 2 users have registered over some domain.com server using LTE + IMS backbone. Now by default in a VoLTE network the default bearer is established with QCI=5 (Reserved for IMS Signaling).
-> Now UE2 makes a video call to UE1. Since UE1 has just registered on the domain.com server (IMS server) so it is having only one default bearer with QCI5,
-> Here in this scenario since a VoLTE video call requires both QCI=2 for video and QCI=1 for audio, the Network will trigger ERAB setup request at UE1 end (MT or mobile termination end). There will be ERAB setup request for QCI1 and QC2 both network triggered for UE1 as UE1 here is Called party.