SRVCC in LTE

SRVCC( Single Radio Voice call continuity):-  SRVCC is a feature/process by which a voice call(VoIP) in LTE can be continued in legacy RAT(2G/3G, CS call) via handover when UE moves out of LTE coverage. 

Why its called Single Radio?- The process is called single radio is due to only a single radio is required in the handset.

Call Flow for SRVCC:- Here below I m indicating the simplest way of SRVCC call flow.

The process:- When UE moving away from LTE coverage then UE notifies the eNodeB(By sending measurement reports). Then eNodeB informs MME to make a decision for handover to legacy RAT network.

We are defining thresholds of SRVCC for serving cell by Inter-RAT B1 and B2 thresholds.

Note: We can set a greater threshold in case of TTI bundling feature is enabled. As with TTI bundling feature VoLTE services can be improved at cell edges.

https://mytechnew2019.blogspot.com/2019/02/tti-bundling-in-lte.html

New Interface: For SRVCC implementation  3GPP introduces a new interface called Sv. The Sv interface is from MME to MSC.

Elements of SRVCC Network Architecture:- Here we are discussing about some important network elements which play a big role in SRVCC.

Sv interface:- Signalling interaction for SRVCC handover as an interface between MME and MSC server.

eNodeB:- SRVCC indication to MME with help of UE measurement reports.

MME:- Bearer splitting for Voice and Non-Voice services and MSC selection.