Need to test your MCPTT (Mission Critical Push To Talk) solution including latency ?

While First Responders are gradually migrating from so-called legacy radio media to the use of 4G and 5G mobile networks, control needs are increasing. 

The Réseau Radio du Futur project initiated by the French Ministry of the Interior is a perfect illustration of these needs. 

The use of deployed operator networks for the transmission of critical flows requires controlled performance of these flows in quality of service. It is therefore essential that the latency in MCPTT is controlled.

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 MultiDSLA, supports Mission Critical players in the validation and supervision process for associated metrics and KPIs 

Thus, we help those who protect us to protect us. 

Want to know more ? ask for our white paper here.

Contact Opale Systems or your distributor for more information.

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