Most people in the wireless ecosystem understand the inherent value proposition of LTE: more efficient spectrum utilization and better end-to-end QoS capabilities due to its new internet protocol (IP) network architecture. What many don’t understand is that the initial deployments of LTE, which consider all sessions as data, do not support voice calls “as data”. This excludes over-the-top (OTT) calls made through Skype, Google Talk or Viber, that would be detected by the network as being an anonymous data application. These VoIP applications are generally understood to be best-effort services as opposed to the “network-quality” voice that most mobile subscribers have come to expect.
Until an operator deploys voice-over LTE (VoLTE), LTE voice calls are supported in the 3G network through an implementation known as Circuit Switched (CS) Fallback in 3GPP networks. While CS Fallback is an interim measure - via core network upgrades - until a more robust VoLTE implementation is deployed, operators are often unaware of the unintended consequences on their LTE and 3G network.
When an LTE subscriber makes or receives a voice call, the network redirects the device to the 3G network where the voice call is attempted. Upon completion of the voice call and any active data session, the device must reselect the LTE network. An unintended consequence of this standardized approach to call completion is that if an LTE subscriber is using an application (e.g., Facebook) on the 4G network at the time of the call, both the voice and data session are moved back to the 3G network. Perhaps even more troubling to the network operator, until the data session is completed or the device is reset, the subscriber will camp on the 3G network. This has a whole host of ramifications to the LTE operator employing CS Fallback, including:
- Over-Capacity of 3G networks
- Underutilization of their LTE network
- Subscriber perception that the 4G data experience is no better than 3G
Like any new technology, there are bound to be challenges in initial LTE network deployments, but the shortcomings of CS Fallback can be addressed. Until recently, operators were unaware of the performance of their LTE network. By adopting next-generation visualisation and optimisation technology operators have the means to understand the performance of their LTE network in real time. Engineers can pinpoint where throughput rates are good, and in some cases bad. By having sight of where LTE subscribers are camped on a 3G network, they can resolve the issue by optimising existing network equipment, or deploying small cells, to increase capacity.