VoLTE Interoperability—It can Make or Break the VoLTE Experience


Test methodologies for VoLTE should address the VoLTE interoperability challenges to deliver on the guaranteed QoS advantage over the OTT services

2005. I remember it vividly as that was the year I got my first 3G smartphone. 10 years later, I still consider it a prized possession because it was way ahead of its time with a 32MB RAM and a front facing VGA video call camera. It was the talk of the town and surely a conversation starter. Being an early adopter, I was never able to make a video call. Although my phone supported the feature, the wireless carriers did not. But I knew this was the future, and a year later the industry saw its first iPhone and things started changing for 3G. Then there was Android, and as HSPA+ rolled out, suddenly even the thought of going back to the 2G speeds would make people cringe. Along came the OTT VoIP applications that changed the game of the voice calling services but with the caveat of “best effort” internet delivery that did not take quality of services into account.

As we head to a more interconnected world with continuously evolving wireless standards that offer better technological convergence, the need for better Quality of Services has become imperative. The true measure of progress in this industry is not how fast you can go, but how fast you can go, reliably.  Voice over LTE or VoLTE is the answer to this need, providing guaranteed quality of services (QoS) and exceptional HD voice quality.


Deployment for any leading edge technologies has always been challenging and such is the case with VoLTE. There have been a lot of technical and non-technical obstacles that VoLTE deployment has faced, but the VoLTE adoption has finally paved its way into commercial release realm- with over 70 carriers investing in VoLTE across 36 countries in 2014.  Yet this significant technology faces a major challenge that needs to be addressed – VoLTE interoperability. 

The Interoperability Complexity

The interoperability equation has exploded for VoLTE. Why, you may ask? The reason being- VoLTE’s device to device nature, which means that every endpoint in this ecosystem operates with every other endpoint to carry out the simple function of voice calling. While, this may seem simple to the end user, it is fairly complex with endpoints negotiating with each other, with every endpoint interoperating with every other model from every other manufacturer, regardless of version, and across every carrier’s network.  The individual and proprietary nature of each provider’s IMS core adds to this existing complexity.


Some specific factors that affect the VoLTE interoperability are:

  • SIP Signaling: Due to the loosely defined nature of the SIP signaling protocol, VoLTE call failures may occur because of syntactical differences in the SIP messaging format. 

  • Initial SDP negotiations (both Narrowband and Wideband): As part of the SDP negotiations, different payload types are presented from the “calling” UE to the “called” UE in a particular order of preference. If this preference is not interpreted correctly, the call quality suffers. 

  • Device-to-device codec negotiation: Codec negotiation plays a crucial role in determining the quality of user experience as the codec used by one device may not be compatible with the other device. This results in the device choosing the Lowest Common denominator for the codec resulting in substandard call quality. 

  • RTCP negotiation failures:  RTCP negotiation disagreement from either UE on the QoS requirement can cause call failure. 

  • Jitter buffer management: Good jitter buffer management algorithms are required to support the high quality voice that is expected of VoLTE, and if this requirement is not met, the excess jitter can result in poor call experience. 

How to solve the problem?

The only real way to head off these issues is to invest in device-to-device testing in the lab, before new devices are launched on the live network and in the hands of the user.  Early detection of these issues in the lab enables faster and cheaper recovery; speeds time to market; and reduces interoperability concerns. The classic call-box type of emulators can’t handle this challenge, and this calls for a solution that addresses the need of both developers and testers to have a device-to-device concept in every element of the system that works together to handle this granular concept of interoperability. Test methodologies for VoLTE should address this interoperability challenge and deliver the promised Quality of Service that makes VoLTE superior to OTT VoIP services.




Sneha Patni
Sneha Patni

Technical Marketing Engineer, Spirent Communications

Sneha Patni is a Technical Marketing Engineer working at Spirent Communications’ Wireless business unit. As part of her role with Spirent, Sneha interfaces with global cross functional teams to drive sales and translate business objectives into product strategy. She is a passionate tech geek and has four years of wireless industry experience with companies like Mediatek and Blackberry, with experience ranging from testing mobile application technologies to handling certification test lab. Sneha has a master’s degree in electrical engineering from University of Florida.