【LTE FDD Answer House】What Are the General Principles for Voice Policy Selection

 What Are the General Principles for Voice Policy Selection?

Question

What are the general principles for voice policy selection?

Answer

During the UE attach and TAU period, the MME selects a voice policy based on the reported UE capability and voice policy configurations on the MME. The MME then sends the UE the voice policy contained in the Attach Accept message. The general principles that the MME selects a voice policy for UEs are as follows:

• UEs supporting only CS fallback select the CS Voice only policy, that is, CSFB.
• UEs supporting only IMS select the IMS PS Voice only policy, that is, VoLTE.
• For UEs supporting both CSFB and IMS, the voice policy is specified by operators when the UEs are registered.

Applicable Versions

eRAN6.0 and later

Hi Helene,

We are observing some terminals, which are manually locked to the LTE by their users,
but anyway sending Extended Service Requests (for example due to USSD). In such
scenario MME triggers CSFB procedure despite the fact that UE reported only
eutran capability. Problem is with eNodeB, which is not trying to perform any
redirection but sends regular RRC release with cause “other”. As a result
CSFB execution is treated as not successful and CSFB Success Rate KPI is deteriorated.

Question is if there could be any switch forcing eNodeB to send RRC Redirection to legacy RAT in case if only eutran capability was reported by terminal which is sending Extended
Service Requests?

Kind Regards!

Jacek