CC BY-SA 4.0Kara, ErdemErdemKaraModroiu, Elena RamonaElena RamonaModroiuCorici, Marius-IulianMarius-IulianCoriciMagedanz, ThomasThomasMagedanz2025-11-172025-11-172025https://publica.fraunhofer.de/handle/publica/49941310.1145/3750718.375074510.24406/publica-64332-s2.0-105020669729First responders require ultra-reliable, low-latency communication and push-to-talk (PTT) features for effective crisis response. Current mission critical PTT (MCPTT) implementations typically rely on proprietary solutions, limiting deployment flexibility in private 5G networks. This paper presents a novel proof-of-concept implementation of an open-source MCPTT system by integrating various open-source projects to meet 3rd Generation Partnership Project (3GPP) requirements and enabling broader accessibility. The system architecture is outlined, highlighting the functionalities of its components. We detail the configuration of the testbed and the selected open-source projects used to integrate a complex MCPTT service. We also provide the key MCPTT functionalities implemented in the developed system within a private 5G network. Our evaluation methodology is based on several key performance indicators (KPIs), including MCPTT access time, end-to-end MCPTT access time, and mouth-to-ear latency. Although the initial performance measurements do not fully satisfy the defined limits, they achieve promising results, revealing areas for further improvement. This work advances the field by demonstrating the feasibility of an open-source MCPTT solution and provides valuable insights for future developments in mission-critical communications.entrue3GPP5GCampus NetworksFloor ControlKPIMCPTTMission Critical CommunicationsOpen SourcePrivate 5G Networksconference paper