Interworking and voice call continuity

Interworking is required between VoNR-capable networks and the other legacy networks due to legacy subscribers, coverage gaps, and utilization of other radio technologies.

The subscribers of 2G, 3G, and fixed-lined subscribers on Public Switched Telephone Networks (PSTN) do not support SIP signaling. Therefore, the communication between legacy subscribers and a VoNR subscriber requires appropriate SIP-based signaling and Real-Time Transport Protocol (RTP)-based voice packet conversion.

In the rollout of each new technology, there exist some coverage gaps in RANs. So, in these coverage gaps, the subscribers need to hand over to other technologies for connectivity continuity. This is also valid for 5G rollouts. As the 5G networks roll out, there will be some coverage gaps that affect the VoNR subscribers in terms of call continuity. Therefore, some handover techniques from 5G to legacy networks, such as 4G or 3G, are required.

Finally,...