ng an ongoing VoLTE call becomes difficult, EPS VoLTE bearer connection can be handed over to CS connection in 3G or 2G network. The procedure that provides the means to the handover is SRVCC. 14.5.1 Signalling Flows UE and MME Capability Attach and Tracking Area Update The SRVCC UE informs the network about its capability of performing SRVCC in the Attach Request message and in Tracking Area Update: The UE includes the SRVCC capability indication in 'MS Network Capability' IE where SRVCC to GERAN/UTRAN capability is set. If the SRVCC UE supports GERAN access, it includes the GERAN MS Classmark 3 MS Classmark 2 is included if GERAN or UTRAN access or both are supported. The supported Codecs IE is in the Attach Request message and in the non-periodic Tracking Area Update messages. Context Setup When a new context is set up in eNodeB, the eNodeB gets informed about UE and MME SRVCC capabilities. The MME informs the eNodeB by including 'SRVCC operation possible' indication in the S1 AP Initial Context Setup Request. Intra-EUTRAN Handover and EUTRAN to UTRAN Iu Mode Inter-RAT Handover In case of handovers, both the UE and MME SRVCC capabilities need to be transferred to the target MME, target SGSN and target eNodeB. In case of an intra-EUTRAN S1-based handover and EUTRAN to UTRAN Iu mode inter- RAT handover procedures, the source MME sends MS Classmark 2 and 3, STN-SR, C- MSISDN, ICS Indicator and the Supported Codec IE to the target MME/SGSN. 'SRVCC operation possible' indication is included by the target MME in the S1-AP Han- dover Request message and in case of IRAT HO, the target SGSN includes the indication in the RANAP Common ID message. In case of X2-based handover, the source eNodeB includes a 'SRVCC operation possible' indication in the X2-AP Handover Request message to the target eNodeB. VoLTE Optimization Ongoing VoLTE EUTRAN UTRAN First measurement Report (A2) call (PS) in source network Measurements, RRC Conn Reconf (meas gap) eNB HO decision, CN preparations Second measurement Report (e.g. 3G RSCP=20) H