As First Responders progressively migrate from legacy radio systems to 4G and 5G mobile networks, the need for robust control and performance monitoring is increasing.
The “Réseau Radio du Futur” project, initiated by the French Ministry of the Interior, perfectly illustrates these evolving requirements.
With critical communications now relying on commercial mobile networks, it is essential to ensure controlled Quality of Service (QoS) for the transmission of mission-critical data. In this context, latency control in MCPTT (Mission Critical Push-to-Talk) communications becomes a key factor to guarantee fast and reliable response capabilities.
Why and How to test latency for audio in MCPTT ?
While voice quality and intelligibility are important, end-to-end latency is a critical factor for field workers. PTT terminals and applications must enter the latency budget.
Poor communication, too high latency, unstable or a terminal that absorbs jitter inappropriately and it is the action of field agents and the securing of teams and victims that presents a risk.
This is why 3GPP and ETSI define 4 essential KPIs for voice oriented latencies.
4 KPIs to measure audio latency
It is up to the actors, in the objectives of validation in the laboratory, in deployment and in production, to measure quality, intelligibility and latencies.
Here is an abstract of the 3GPP/ETSI standards defining the 4 latency KPIs:
“MCPTT Access time (KPI 1). The MCPTT Access time is defined as the time between when an MCPTT User request to speak (normally by pressing the MCPTT control on the MCPTT UE) and when this user gets a signal to start speaking. This time does not include confirmations from receiving users.”
“The End-to-end MCPTT Access time (KPI 2) is defined as the time between when an MCPTT User requests to speak (normally by pressing the MCPTT control on the MCPTT UE) and when this user gets a signal to start speaking, including MCPTT call establishment (if applicable) and possibly acknowledgement from first receiving user before voice can be transmitted”
The Mouth-to-ear latency (KPI 3) is the time between an utterance by the transmitting user, and the playback of the utterance at the receiving user's speaker”
“The Late call entry time (KPI 4) is the time to enter an ongoing MCPTT Group call measured from the time that a user decides to monitor such an MCPTT Group Call, to the time when the MCPTT UE's speaker starts to play the audio. The performance requirements for Late call entry time only applies to when there is ongoing voice transmitted at the time the MCPTT User joins the call.”
To learn more about these KPIs, you can consult chapter 6.15 of the following recommendations (last update April 2022):
In fact, measurement methods and tools are a necessity.
The DSLA is a hardware box that connects to the terminals in order to provide 3 of the 4 essential KPIs in terms of latency. (KPIs 1,2 and 3). The P.863 standard is also supported for the audio quality measurements defined by these standards.
The latest KPI (KPI 4) will be made available through the VPP software tool, SIP client, whose MCPTT functionalities will be implemented by June 2023. A workaround is also possible through MCPTT application automation and MultiDSLA automation.
What can Opale Systems do for you to mesure the latency for audio in MCPTT ?
Opale Systems, through its MultiDSLA platform, supports Mission Critical communications stakeholders in the validation and supervision of key performance metrics and KPIs.
In this way, we contribute to ensuring the reliability and effectiveness of the critical services that safeguard public safety.
Opale Systems
Monday, 9th January 2023 
