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Skylo’s Work on Making NB-NTN Voice a Reality

At the Global 5G Evolution Workshop a couple of months ago, Soham Desai, Staff Wireless Systems Engineer at Skylo, delivered an insightful session on the progress of voice over NB-NTN and why this capability is now becoming practical. His talk walked through the state of the technology, the recent advances that make narrowband satellite voice possible, and the work being done in 3GPP to support it.

Soham began by introducing Skylo and its role in enabling direct-to-device (D2D) satellite connectivity. Skylo works with a wide ecosystem that spans chipset vendors, device manufacturers, carriers and test equipment providers. The company promotes a hybrid approach that allows a single device and SIM to move seamlessly between terrestrial networks and Skylo’s satellite network whenever coverage is needed. A large number of consumer devices, including popular smartphones and smartwatches, already use Skylo’s services for satellite SOS and messaging, supported by a growing base of partners and activated users.

The focus of the talk was on why NB-NTN voice matters and why the timing is right. Geostationary satellites are already in orbit with vast coverage footprints, and 3GPP has been progressing work to support narrowband voice services in Release 20. One of the most important enablers is the arrival of very low bitrate AI-driven codecs that maintain high audio quality even at around 1 kbps. This is essential, because narrowband satellite links have strict bandwidth constraints.

Soham also highlighted the benefits of using non-IP data delivery (NIDD) instead of traditional IP traffic. For narrowband systems, removing unnecessary IP and UDP overhead provides significant efficiency gains, especially when compared with robust header compression. Skylo’s approach combines these efficiencies with a dedicated voice gateway that allows operators to continue using their existing SIP-based infrastructure while the device communicates over the satellite link using I1 protocol messages. This keeps the signalling footprint small and improves call setup times. While SIP usually requires many transactions to establish a call, I1 can achieve the same outcome in only a few messages, which is particularly valuable on long-latency satellite links.

The talk also touched on current 3GPP work to refine signalling and user-plane support for NB-NTN voice over GEO systems. There is ongoing activity in Service Architecture (SA) Group 2 on improvements that reduce delays and optimise both SIP and I1-based procedures for satellite conditions. A number of companies, including Skylo, are contributing to this effort.

Soham concluded with a demonstration of Skylo’s voice architecture as it operates today. Using a standard NTN-capable handset, Skylo’s core network and its voice gateway, calls can be delivered to a SIP client through an operator’s existing infrastructure. This shows that narrowband satellite voice is no longer experimental. It is already functioning in real systems and is moving rapidly towards broader adoption.

You can watch the full talk from the workshop below.

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