Global adoption and accessibility

VoLTE is formally defined in GSMA specification IR.92 for voice and Short Message Service (SMS) in LTE, which has its origins in the 3GPP IMS-based multimedia telephony (MMTel) solution.  VoLTE has widespread backing in the telecoms industry with more than 40 key players declaring their support for it at the 2010 GSMA Mobile World Congress in Barcelona and many more have done so since. Leading operators started to launch VoLTE-based services in 2013 and many GSM/WCDMA and CDMA operators are planning to deploy VoLTE based on IMS.

As a consequence of being a globally adopted standard, subscribers will be able to experience VoLTE services across the globe in the same way they experience voice and data service accessibility when travelling from country to country. 

Richer sets of features

Subscribers will experience a far richer set of features to those currently experienced by OTT services.   For example,  users can start a voice session then add and drop media such as video and add callers.  VoLTE operators will evolve their voice services into rich multimedia offerings, including HD voice, video calling and other multimedia services such as Rich Communication Suite (RCS).

Guaranteeing QoS and QoE for VoLTE applications

So how do operators ensure that VoLTE and other services on LTE are delivered with comparable QoS to their switched circuit networks, and how they then measure the quality of experience (QoE) of applications, such as VoLTE, being delivered on top of LTE?

QoS vs. QoE

Let’s first clarify what is meant by QoS and QoE.

“Quality of Experience” (QoE) is a term that is commonly used when dealing with quality-sensitive services, such as real time video and audio. It refers to the perceived quality of the end-to-end services as consumed by the subscribers.

In its strict sense, QoE is understood as a measure mapping human perception onto a scale of 1-5: 1= bad, 2= poor, 3=fair, 4=good, 5=excellent, with the minimum threshold for an acceptable QoE being 3.5 (/ITU-T P.800/). This is obtained by the manual assessment of individual user’s experience and this is referred to as “mean opinion score” (MOS).

QoE is impacted by various parameters in multiple layers. As far as these parameters are measurable, these are commonly denoted by the term “QoS”. Therefore, “QoE measurement” is a two-step approach:

1. Measuring QoS parameters which are most indicative and complete in characterizing QoE.
2. Estimating QoE based on the measured QoS parameters. For real time video and audio, there exists a large variety of models that explicitly calculate MOS scores based on measured QoS.

The QoE metrics are categorized into the following three categories:

1. Accessibility: access failures and access times
2. Retainability: drops of ongoing sessions
3. Quality (or Integrity): quality as perceived during service usage

 The definitions of QoS and QoE have a subtle, but important difference:  Service and network performance (QoS) is what operators can monitor and manage to ensure delivery of good customer experience (QoE) of a particular application.

This difference becomes crucial for operators who must ensure that VoLTE and other LTE services are delivered with a comparable QoS as those on the traditional circuit switched services.

To deliver this, the operators need to both monitor and manage the QoS of the actual network and service, and measure the QoE for the users of the VoLTE application.