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Comprehensive Testing of Mission-Critical Push-to-Talk (PTT) solutions for a leading UK Mission-Critical Communications provider 

Overview

A leading UK-based Mission-Critical Communications provider engaged us to conduct comprehensive testing for their Push-to-Talk (PTT) solution. The client required a rigorous testing strategy to validate the reliability, performance, and failover resilience of their PTT services across LTE networks, ensuring seamless and uninterrupted communication for emergency responders and enterprise users.

Our Solution

Integration Testing:

  • Validated interoperability between PTT core, EPC, RAN and external applications.  

  • Identify and mitigated integration failures through detailed log analysis.

  • Ensured seamless interworking with non-3GPP systems like TETRA and WiFi

  • Addressed challenges in API interactions

Performance Testing

  • To replicate real-world conditions, we combined real UEs with a load simulator, measuring

    • Call setup time

    • Group call setup time

    • Call setup success rate

    • Call drop rate

    • Data throughput

    • Packet Loss rate

    • Speech Delay

    • Quality of Experience (QoE): Voice clarity, video quality and Latency
       

Our approach involved:

Ramp-Up Testing: Gradually increasing load to identify performance bottlenecks.

Steady-State Testing: Maintaining constant load for sustained stress validation.

Ramp-Down Testing: Observing system recovery after peak usage.

Primary Objectives 

Validate reliability, performance, and failover resilience of their PTT services across LTE networks

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Scope of Work:

  • Integration of PTT services with other systems, such as dispatch consoles, emergency response platforms, and interworking with TETRA network.

  • Functional Testing: Ensuring end-to-end functionality of PTT services, including initiation, emergency call, group call, late call entry, floor control, priority handling and interworking with legacy systems.  

  • Performance Validation: Measuring key performance indicators (KPIs) like Call setup time, Group call setup time, Call setup success rate, Call drop rate, Data throughput, Packet Loss rate, Speech Delay, Voice Quality, Video Quality and Latency under real-world conditions.

  • Failover Testing: Guaranteeing uninterrupted services in case of network failures, including intra-site and inter-site redundancy.

  • End-to-End Automation: Automating critical PTT call flows to enable rapid feature validation and regression testing.

  • Concurrency: Managing a large number of simultaneous 1-2-1 calls, group calls, and other interactions without conflicts or errors.

  • Priority & Pre-emption: Prioritising PTT calls over commercial traffic and ensure their reliable delivery even under heavy load

Automation of PTT Call Flows

  • Automated critical call flows, including 1-2-1 call, group call, broadcast calls, Emergency Alerts & Calls, Call Upgrades/Downgrades between emergency & standard calls, Late Entry, Priority Talkgroup Scanning & Call Management and broadcast messages.

  • Enable continuous testing for faster regression cycles

  • Reduced manual effort while ensuring repeatability and accuracy

End-to-End Functional Testing

  • Subscriber Life Cycle Management: Validating provisioning, authentication, MSISDN Change, SIM and Device change.

  • PTT Services: Verifying 1-to-1, group, broadcast, and emergency call handling, along with advanced features like ambient listening and Discreet Listening, and VoLTE interactions.

  • Video & Messaging Services: Ensuring smooth PTT video calls, multimedia messaging, and secure text communications.

  • Presence & Location Services: Tracking real-time user availability and location updates for situational awareness.

  • Mobility & Interworking: Ensuring smooth transitions across networks and interworking with non-3GPP systems (TETRA and WiFi).

Key Outcomes

We executed real-world failure simulations to ensure service continuity across multiple layers

  • Successfully validated the end-to-end PTT solution in accordance with 3GPP specifications (TS23.379, TS23.280, TS23.281, TS23.282, TS23.283, and TS23.289), ensuring full compliance with mission-critical communication standards.

  • Identified and resolved integration challenges (RAN Integration, EPC Integration, PCRF Integration, Integration with User Organisation Control Room)

  • Reducing the call setup time from 600+ms to <= 260ms

  • Improved voice quality improved MOS from 2.6 to 3.8 at cell edge

  • Our in-depth analysis identified key issues in RAN scheduling, providing critical insight that enabled the RAN design to optimise the PTT traffic prioritisation over commercial traffic.

  • Our detailed analysis enabled the design team to improve the ROHC algorithm, achieving compression gains of approximately 90%(from 55%), reducing packet loss to less than 2% (from 10-12%), and a 20% reduction in bandwidth usage.  

  • Automation of 80% of critical PTT call flows led to 40% faster testing cycles, reducing time-to-market

  • Proven Operational Resilience: Real-world performance testing with 300 real UEs and load simulators ensured the system meets operational demands and guarantees failover resilience for uninterrupted service

  • Performed long duration stability tests to ensure 99.99% availability

  • Failover testing ensured failover time was < 2seconds to secondary nodes / data centre

Failover Testing

We executed real-world failure simulations to ensure service continuity across multiple layers

  • Tested failover and redundancy mechanisms to ensure continuous service availability.

  • Simulated network node failures, inter-site failovers, and transport link disruptions.

  • Validated seamless recovery in scenarios like EPC node failures, IP transport failures, and application server failovers

Failover Testing

We executed real-world failure simulations to ensure service continuity across multiple layers

  • Tested failover and redundancy mechanisms to ensure continuous service availability.

  • Simulated network node failures, inter-site failovers, and transport link disruptions.

  • Validated seamless recovery in scenarios like EPC node failures, IP transport failures, and application server failovers

Conclusion

Our expertise in Mission Critical PTT testing, combined with a structured approach to Integration Testing, End-to-End Testing, Automation, Performance Testing, and Failover Validation, ensured that the solution met the stringent demands of mission-critical communications. With robust test artifacts, automation frameworks, and real-world load simulations, we accelerated testing while maintaining the highest quality standards.

Our engagement reinforced the client's confidence in their PTT solution, enabling them to deploy a highly reliable, scalable, and resilient communication system for mission-critical operations

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Capabilities and Expertise

  • Comprehensive Test Artifacts: Ready-to-use test artifacts covering end-to-end scenarios, adaptable to various PTT solutions and requirements.

  • Scalable Testing: Capability to test with up to 300 real UEs simultaneously, providing realistic performance validation at scale.

  • Deep Expertise: 8 years of experience in mission-critical testing and 16 years of experience in telco testing, coupled with specialised knowledge of MCPTT solutions.

  • Automation Testing Framework: Robust automation framework for rapid and efficient testing of critical call flows.

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