# Practical Performance Analyses of 5G Sharing Voice Solution
## 4 Voice Services Based on 5G Sharing
### NSA Sharing VoLTE Process  
In NSA networking architecture, voice service is provided by VoLTE, bearing in LTE. NR is not involved in voice service. Voice continuity interoperability between 5G and 4G is not considered. At this time, UE needs to enable the VoLTE feature and support dual connection, supporting data transmission and reception on 5G and 4G radio access at the same time. The advantage of this solution is its minimal impact on the 4G core network. The disadvantage is that, if switching to 2G/3G with SRVCC, the NR link will be removed, and data service rates will deteriorate rapidly. This paper proposes two implementation solutions of VoLTE bearer for NSA users. The first type is VoLTE bearing in the 4G shared anchor cell of the contractor. Users can reside in anchor points for VoLTE service. In this way, VoLTE directly initiates on the current resident operator. It only needs to configure the sharer VoLTE to be carried on the 4G carrier according to the business priority policy. This solution has less access delay. The second type is that VoLTE is carried on the home 4G cell, and when VoLTE service is established, a service-based handover to the respective home 4G network is established. The focus of this solution is how the 5G UE can realize the VoLTE service bearing on the home 4G network. This solution requires the shared anchor eNodeB of the contractor to support the PLMN-based configuration of the neighbor list and frequency priority setting based on PLMN. The VoLTE must be configured based on the service priority policy to be carried on the specific 4G carrier first. In the shared area, the 5G UE resides on the 4G anchor point of the contractor. When the 4G anchor point of the contractor receives the request for VoLTE initiated by the 5G UE, i.e., setup request of quality of service (QoS) class identifier (QCI) 1, the 4G anchor point of the contractor triggers the service-based inter-frequency handover so that the 5G UE returns to the specified 4G for VoLTE service. In this way, each shared operator has an LTE carrier specifically bearing the VoLTE feature. However, the sharing VoLTE user makes an additional inter-frequency handover at the initiation service stage, which increases the VoLTE access delay. The handover flow is shown in Figure 4.  
As can be seen in Figure 4, in the handover process, the sharer EPC first initiates an evolved radio access bearer (E-RAB) setting a request message to the contractor anchor eNodeB. The contractor anchor eNodeB initiates an RRC connection configuration instruction to the sharer UE based on the service handover measurement. After receiving the configuration completion feedback, the contractor anchor eNodeB sends an E-RAB setting response to the sharer EPC to complete the E-RAB setting process. After receiving the measurement report of the sharer UE, the contractor anchor eNodeB sends a handover request to the sharer EPC. Interaction is performed between the sharer EPC and the sharer eNodeB to complete the handover request confirmation. The sharer EPC sends a handover command to the contractor anchor eNodeB. Afterward, the SgNodeB release can be performed between the anchor eNodeB and gNodeB of the contractor, and this step is optional in voice service. After the contractor anchor eNodeB sends the RRC connection configuration to the sharer UE, the UE feeds back a completion indication of the RRC connection configuration to the sharer eNodeB. Finally, the sharer eNodeB sends a handover notification to the sharer EPC to complete the handover process. The symbols used to evaluate the communication costs are listed in Table 1. For each handover protocol, all the communication costs of the handover phases are summed to represent the communication cost for that protocol. These symbols are used to represent the cost of communication between different entities. Figure 4: Service-based inter-frequency handover process for voice over LTE (VoLTE).