Migration from EPS Fallback to support voice in 5G

While Evolved Packet System (EPS) fallback is recommended for early 5G system deployments, support of voice in a 5G system is required sooner or later. The migration from EPS fallback to support voice in a 5G system must be as simple as possible.

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Voice over NR

If you followed my earlier blog posts 5G voice for smartphones: Network prerequisites and Voice in 5G system—architecture and EPS fallback, you have learned what the first network evolution steps and pre-requisites are to enable 5G voice on smartphones. So, the next step to look into is how to enable voice over NR (New Radio).

Voice over NR implies that voice calls can be made on NR (standalone (also known as option 2 in the industry)). This requires all system components including the device to support all voice related capabilities and intersystem handover. It also requires that NG-RAN (New Generation Radio Access Network) is dimensioned and tuned for voice—you simply don’t want to have too frequent handovers, or even dropped calls.

Besides voice as such, regulatory requirements for emergency calls must also be addressed. Depending on those requirements, the technical details may differ on how to ensure that an emergency call can be established.

Handling of voice and emergency calls on NR requires that both NR and devices support the quality-of-service (QoS) flow for voice over the radio access, i.e. the QoS flow establishment for voice is supported by NR base station (gNodeB). The NR gNodeB may initiate an inter-system handover to EPS (Evolved Packet System) at any time later, based on measurement reports provided by the device. 



Migration from EPS fallback to voice over NR

The network-based solution for EPS fallback allows migration to voice over NR. This migration is accomplished by changing the RAN configuration to not always trigger fallback at QoS flow establishment for voice, but instead to let the QoS flow for voice be established on NR connected to 5G Core.

This migration can be done once all required voice capabilities are in place in the network. Devices introduced before this step will be still in the field when voice over NR is introduced in 5GS. The capabilities of these devices will determine if the devices will use voice over NR or continue to rely on EPS fallback.

So this was a brief intro about how to enable voice over NR, you can read more in the brochure that is available for download. In my next blog post I will share more aspects you need to consider when enabling 5G voice, such as radio coverage aspects and what the next industry steps could be.

Do you want to know how to take the steps towards 5G voice in your network? Learn more about the network architecture for 5G voice and our recommendations how to evolve your network.


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