How network tell UE that VoLTE is configured?

In which SIB it is communicated to the UEs that the network is VoLTE configured?

Only after that VoLTE Capable & Core Configured UE will set up both QCI-9 and QCI-5 bearers whenever they send the attach request to the network?

Sib1 having IMS emergency related flag.
Never seen such other flag for VoLTE.
Infact UE indicates to network related to VoLTE capability in attach request, then procedure started.

VoPS support of the network is given in attach accept.
SIB 1 has only emergency related info which is helpful to quickly skip networks which don’t support e911 when UE scans through multiple networks.

So the network never informs about being VoLTE Configured?
The first it will be UE who will share with the network that it has VoPS (VoLTE) capability and it prefers to use VoLTE.
Knowing this core will initiate ERAB setup inside Initial Context Setup Request of QCI-9 and QCI-5 for the UE.

UE will also send 2 times PDN connectivity request for each default bearer.
QCI9 and QCI5 for signalling.

Thats from Attach Accept/Reg Accept, IMS VoPS/IMS over 3GPP supported bits, after that UE sends IMS PDN/PDU.

Not necessarily, in LTE, UE can attach with default or IMS pdn and can request other separately after attach.

If a LTE network doesn’t support VoLTE, it should atleast support voice fallback services on 2g/3g.
So, there is no need to tell this capability before attach itself.

SIB is from RAN configuration.
VoLTE requires Core Network support.
So SIB cannot show VoLTE capability of network.
It’s sent to UE in attach accept from MME.

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4 steps:

  1. RRC CONNECTION SETUP
  2. QCI 5 BEARER SETUP
  3. UE & IMS NEGOTIATION STARTS
  4. QCI 1 BEARER SETUP TO CARRY VOICE FRAMES

Before that the network ask about UE capacility to know if the UE supports VoLTE Feature or Not.