By: Jean Jones, Director, Wireless Marketing, Alcatel-Lucent
What does voice over LTE (VoLTE) offer your subscribers? Better voice quality, including HD voice. Rich communications with messaging and video. And whatever inventive applications you choose to introduce. In other words, VoLTE can provide a superior quality of experience (QoE) for subscribers and give you a competitive edge — particularly when your service operates at its best. 
In my last blog, our experts explained why an end-to-end strategy is the key to maintaining peak VoLTE performance. Now we’ll look at how this strategy gets put into practice to optimize real-world service offerings. The information here is based on interviews with Luis Venerio who works with our VoLTE Readiness Services team. And his observations come straight from his experience on VoLTE deployments that serve millions of subscribers.
Validating QoS end to end
The first step in providing a satisfying QoE is to make sure each element of the network is correctly configured for VoLTE. That means checking quality of service (QoS) settings, end to end, to verify that all impacted network elements provide the proper treatment to high-priority VoIP traffic. By locating any incorrect settings, this audit identifies where problems can be prevented and performance can be enhanced.
Luis points out that it’s not unusual for network operators to conduct audits. But for VoLTE offerings, there’s an important difference: A collaborative, cross-domain approach can produce the best results. That’s because VoLTE calls travel across the entire network, and performance issues often arise at the intersection of different network domains and elements.
For example, while working on VoLTE readiness, Luis’ team examined the user plane and control plane end-to-end paths that support VoLTE service. And they found inconsistent QoS settings on both. “This included inconsistent QoS settings on the ingress and egress interfaces of individual network elements that handle user traffic,” he says, “as well as inconsistent QoS settings for elements sharing a common interface.” 
Because the translations weren’t set correctly in transport, for example, packets in VoIP weren’t getting special treatment. But for VoLTE to be successful, these settings have to be consistent, because if even one network element doesn’t give high priority, it could lead to packet loss and poor call quality. “We were able to give the operators an end-to-end mapping of interfaces where those parameters were not set consistently,” Luis says. “And we indicated which areas uncovered by the QoS audit could have the greatest impact on VoLTE. So the operators could make the changes that are really needed to deliver higher QoE.”
Checking other cross-domain parameters
A configuration audit can address other VoLTE performance issues too. For example, it can verify the activation status of required features needed for VoLTE service in every domain including but not limited to user devices, radio access, backhaul, core network and IMS layer. And it helps make sure that parameters are properly set for key functionality, such as Circuit Switch Fall Back (CSFB) and emergency calling capabilities.
Through this careful attention to detail, the VoLTE Readiness Services team identified incorrect timer values on the IMS layer, which could affect VoLTE call setup and duration. The configurations of individual network element parameters initially seemed to be fine. But with their cross-domain view, the team found that timers came into play between the IMS and LTE layers, and the timers were tearing down calls. “If you only looked at LTE radio access and core network layers,” Luis says, “it would have been challenging to determine why the calls were failing without understanding interactions with IMS layer.”
Measuring QoE after an audit
After the configuration audit is complete, VoLTE performance needs to be evaluated end to end. This assessment should look at both signaling and bearer traffic to identify delay, jitter and packet loss — and analyze KPI metrics for call setup and quality.
There are various ways to measure and quantify performance, but the Alcatel-Lucent VoLTE Readiness Team uses field-proven, automated in-house VoLTE performance tools to streamline data analysis. The tools analyze KPIs across network segments to identify anomalies, outliers or performance problems.
And because a subscriber’s QoE is also a subjective factor, the team also relies on Mean Opinion Scores. “We believe the MOS is an important metric for understanding the VoLTE user experience,” Luis explains. “So MOS samples taken during drive test calls should be correlated with RAN KPIs and network logs. The MOS scores can be affected by any number of issues, such as poor RF, interruptions caused by handovers, codec selection mismatch, and packet loss, just to name a few.
It’s critical to have a well established process in place that addresses all these findings by properly classifying issues and engaging the appropriate domain subject matter experts who can help to further investigate and resolve the problems. A collaborative team effort with key representatives from the network operator and vendor domain experts is essential to ensure adequate support and a successful VoLTE roll-out.”
“Remember the big picture, and examine the small details”
That’s how I would summarize our expert’s advice for maintaining a high QoE. The key is to keep in mind that VoLTE performs best when it is properly configured for the full length of the network. That’s the big picture. But that means paying attention to small details that are unique to this technology, each step along the way. With that end-to-end approach, VoLTE can help you win new subscribers and deliver the superior QoE that can keep them satisfied.
Our next blog asks the experts about key IMS considerations for delivering optimal VoLTE performance.
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Past blogs in this series:
