The Sub-Saharan African telecommunications landscape presents a dual coverage challenge: mobile signal can be unreliable both in rural areas with limited base station density and in dense urban environments where indoor penetration is poor. For this operator, WiFi Calling is not a complementary feature — it is a core element of the voice service strategy.
Business Challenge
The operator faced a structural problem: with no 2G/3G fallback, any gap in LTE coverage directly means a subscriber cannot make or receive calls. This applies equally to rural communities far from base stations and to urban subscribers inside buildings, basements, or areas with congested LTE spectrum.
Key requirements:
- Launch VoLTE as the primary voice service on an LTE-only network
- Launch VoWiFi (WiFi Calling) to extend voice coverage wherever Wi-Fi is available
- Cover both rural areas (low base station density) and urban areas (poor indoor coverage)
- SIM-based authentication — no additional apps or separate SIM cards
- Compatibility with the existing EPC infrastructure
- Software solution deployable on standard hardware — no proprietary appliances
Solution: ePDG by VAS Experts
VAS Experts provided its ePDG (Evolved Packet Data Gateway) — a software-defined solution for launching Wi-Fi Calling (VoWiFi) in MVNO environments. The ePDG works in tandem with the operator’s VoLTE service, sharing the same IMS core, which eliminates the need for a separate voice infrastructure for each access type.
A key factor in selecting VAS Experts was the ePDG’s compatibility with the operator’s existing EPC infrastructure. Testing validated the integration and all key interface interactions required for VoWiFi deployment, including S2b (ePDG–PGW) and SWx/STa (AAA integration).
Architecture overview
| Component | Role in the Solution |
| ePDG (VAS Experts) | Terminates IPsec tunnels from UE devices over untrusted Wi-Fi; forwards traffic to the IMS core via GTPv2 on the S2b interface |
| IKEv2 / IPsec | Encrypted, authenticated tunnelling between the subscriber’s device and the operator network over any Wi-Fi access point |
| EAP-AKA | SIM-based mutual authentication — the subscriber is identified by their SIM card, no passwords or apps required |
| EPC (PGW / AAA) | Operator’s existing Evolved Packet Core; interoperability with VAS Experts ePDG verified through joint testing |
| IMS / VoLTE Core | Shared signalling and media plane for both VoLTE and VoWiFi calls; no separate IMS deployment required |
Implementation Timeline
Lab testing — 2024
Joint interoperability testing of VAS Experts ePDG with EPC, including validation of all interfaces and VoWiFi call flows.
VoLTE launch — 2025
Commercial launch of VoLTE as the primary voice service on the LTE-only network, with the IMS core deployed.
Pilot operation — 2025–2026
The ePDG was integrated into the production network, with VoWiFi introduced in a controlled pilot for selected subscriber groups. Coverage was validated across both rural and urban scenarios.
Commercial launch — Q4 2026
Full commercial availability of WiFi Calling to all subscribers is planned for Q4 2026.
Coverage Impact of VoWiFi
In Sub-Saharan African network conditions, WiFi Calling delivers measurable coverage improvement across both operating environments:
| Scenario | VoWiFi Benefit |
| Rural areas | Subscribers in villages and remote locations with no or weak LTE signal can make and receive calls over any available Wi-Fi connection, using their existing SIM and number |
| Urban indoors | Offices, shopping centres, apartments, and underground facilities where LTE signal is attenuated: VoWiFi seamlessly takes over from VoLTE, maintaining call continuity |
| No 2G/3G fallback | On an LTE-only network, VoWiFi is the only alternative to VoLTE when cellular coverage is unavailable — making it a critical service rather than an optional feature |
Why VAS Experts ePDG
- Confirmed interoperability with EPC — joint testing completed, all interfaces validated
- LTE-only ready — designed for operators without 2G/3G, where VoWiFi is mission-critical
- Software-defined — runs on standard x86 hardware or VM; no proprietary appliances
- Full 3GPP Release 12+ compliance: IKEv2, EAP-AKA, GTPv2, S2b, SWx/STa
- Shared IMS infrastructure with VoLTE — no duplicate core network required
- Vendor-managed integration support from PoC through pilot to commercial launch
- Modular product ecosystem: ePDG, PGW, PCEF, LBS — scalable step by step
