Introduction
With the global shift from legacy 2G/3G networks to all-IP-based LTE networks, Voice over LTE (VoLTE) has emerged as the new standard for high-definition voice services. However, ensuring seamless VoLTE inbound roaming remains a challenge for mobile operators worldwide.
As operators continue to sunset 2G and 3G networks, enabling VoLTE roaming is no longer optional—it is essential for maintaining seamless voice connectivity for inbound roamers. This blog explores how VoLTE roaming works, the challenges operators face, and the best practices for successful implementation.
What is VoLTE Inbound Roaming?
VoLTE inbound roaming allows subscribers from foreign networks (roamers) to access voice services using 4G LTE networks while traveling abroad. Unlike traditional CSFB (Circuit-Switched Fallback), where voice calls are handed over to 2G/3G networks, VoLTE enables HD-quality calls over LTE without dropping to older technologies.
How Does VoLTE Roaming Work?
For an inbound roamer to make and receive VoLTE calls while in a visited network, the following elements must be in place:
- IMS Interconnection: The home and visited networks must have an IP Multimedia Subsystem (IMS) interconnection to handle VoLTE call sessions.
- Diameter Signaling Exchange: VoLTE requires Diameter-based signaling instead of SS7 to facilitate authentication, session setup, and policy control.
- S8 Home Routing (S8HR) or Local Breakout (LBO): Two models exist for VoLTE roaming:
- S8HR: The voice call is routed back to the home network for processing.
- LBO: The voice call is processed in the visited network.
- QoS (Quality of Service) Agreements: VoLTE requires stringent latency and packet loss control to ensure HD voice quality.
- VoLTE-Compatible Handsets: Roamers must have VoLTE-enabled devices that support the visited network’s frequency bands.
Challenges in Implementing VoLTE Inbound Roaming
While VoLTE roaming brings numerous benefits, operators face several challenges:
1. IMS Compatibility Issues
Not all operators have fully deployed IMS or use the same VoLTE implementation standards. Interoperability between home and visited networks is a key issue that must be addressed through rigorous testing.
2. Diameter Signaling and IPX Connectivity
Traditional roaming uses SS7 for signaling, but VoLTE requires Diameter signaling via IPX (IP Exchange) providers. Operators need IPX peering agreements to support Diameter traffic across networks.
3. Policy and Charging Rules Function (PCRF) Interoperability
VoLTE roaming requires seamless integration between the home and visited networks' PCRF to ensure proper policy enforcement, QoS, and charging mechanisms.
4. Emergency Call Handling & Regulatory Compliance
In some regions, local emergency call handling (e.g., 911, 112) is mandated. This means VoLTE calls must be routed appropriately even if the subscriber’s home network prefers S8HR routing.
5. VoLTE Roaming Agreements & Testing
Operators must establish commercial VoLTE roaming agreements and conduct extensive IOT (Inter-Operator Testing) to validate compatibility, call setup times, and voice quality before launching VoLTE inbound roaming.
Best Practices for Successful VoLTE Roaming Deployment
To ensure a seamless VoLTE inbound roaming experience, operators should follow these best practices:
- Deploy IMS and Ensure Compatibility: Ensure the IMS core is ready for VoLTE interconnection with partner networks.
- Leverage IPX for Diameter Signaling: Work with trusted IPX providers for reliable Diameter signaling exchange.
- Choose the Right Roaming Model (S8HR vs. LBO): Depending on technical and regulatory requirements, select the most efficient VoLTE roaming architecture.
- Optimize QoS for VoLTE Calls: Define end-to-end QoS policies with visited networks to avoid call drops and ensure superior voice quality.
- Conduct End-to-End VoLTE Roaming Testing: Perform extensive interoperability testing (IOT) with partners before commercial launch.
- Monitor and Optimize with VoLTE Analytics: Use real-time analytics tools to monitor latency, jitter, packet loss, and other key VoLTE performance metrics.
Conclusion
With the rapid phase-out of legacy networks, VoLTE inbound roaming is critical for providing uninterrupted voice services to international travelers. While implementation challenges exist, collaborating with IPX providers, optimizing IMS interconnectivity, and ensuring QoS compliance can help operators successfully deploy VoLTE roaming.
By taking a proactive approach, mobile operators can enhance the inbound roaming experience, improve customer satisfaction, and unlock new revenue streams in the era of LTE and beyond.