Voice in 5G system—architecture and EPS fallback
To enable 5G voice in 5G devices, there are many network evolution aspects to take into consideration. 3GPP has specified the 5G system (5GS) supporting voice and other services. One aspect to look into is the 5GS architecture, before detailing how voice will be provided in 5GS.
In my previous blog post I introduced the concept of 5G voice, now let’s look into how the 5GS architecture will support 5G voice. Because voice has high requirements especially on the radio deployment (to ensure high call setup rates and low call drop rates), and because it may take a while until these requirements can be satisfied, also a fallback solution from 5GS to EPS (Evolved Packet System), i.e. from 5G to 4G, will be possible. I will share details for both 5G voice and for the fallback solution.
At least initially, a 5G system (5GS) will not be deployed with full network coverage. Therefore, the 5GS needs to be tightly coupled to an existing 4G VoLTE deployment to provide a seamless voice service across the whole network with good characteristics.
The architecture for this tightly-coupled system is based on common nodes in the control and in the user plane and used regardless whether the terminal is on 4G or on 5G. The control plane embraces all signaling between network elements while the user plane carries the IP flows used for voice and e.g. for Internet access.
Early deployments with EPS fallback for voice
EPS fallback enables phones to use the 5GC with NR prior to all needed voice features are in place in the phone and in NG-RAN and before the NG-RAN is dimensioned and tuned for voice. During call establishment the phone is moved from NR (5G) to LTE (4G) and the call is finally established on 5G. So, for an originating call: you dial on 5G but you talk on 4G.
This is an intermediate step towards native support of voice in a 5G system. We have described more technical details in a brochure that you can download, and in my next blog I continue sharing the next mobile network evolution steps for 5G voice.
Do you want to know how to take the steps towards 5G voice in your network to give smartphones and other devices operator voice services? Learn more about the network architecture for 5G voice and our recommendations how to evolve your current network to prepare for 5G.
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