Clear and reliable voice communication is fundamental to safe ATM operations. Controllers and pilots depend on uninterrupted, high-intelligibility voice transmission to ensure accurate and efficient coordination. However, ATM networks often span multiple generations of technology, with voice communications carried over TDM, IP, VSAT, and MPLS infrastructures, each introducing different levels of latency, jitter, and potential quality degradation.

Frequentis addresses these challenges with advanced voice optimisation mechanisms, ensuring that voice services meet the required ATM performance and safety standards. These mechanisms are embedded within the VCX-IP solution, a fully ED-137-compliant voice communication system. The EUROCAE ED-137 standard defines Voice over IP (VoIP) for ATM, including performance thresholds for latency, jitter, and packet loss. However, in operational environments where satellite-based VSAT or other high-latency communication links are used, the 255 ms one-way delay limit set by ED-137B/C can be insufficient. This is especially relevant given that typical VSAT delays in geostationary orbit are around 280 ms, whereas the fastest terrestrial networks operate in the range of tens of milliseconds.

The EUROCAE ED-137 standard defines Voice over IP (VoIP) for ATM, including performance thresholds for latency, jitter, and packet loss. However, in operational environments where satellite-based VSAT or other high-latency communication links are used, the 250 ms one-way delay limit set by ED-137B/C can be insufficient. This is particularly relevant given that typical VSAT delays in geostationary orbit are approximately 280 ms, whereas the fastest terrestrial networks operate in the range of tens of milliseconds. To overcome these limitations, Frequentis has extended the capabilities of ED-137 within VCX-IP, introducing enhanced delay compensation of up to 500 ms. This allows reliable transmission over high-latency networks by dynamically adjusting for network fluctuations. Additionally, VCX-IP employs advanced jitter buffering to ensure smooth and continuous voice delivery, even in variable network conditions. Packet re-sequencing and loss mitigation mechanisms enhance transmission reliability in degraded environments, while adaptive voice compression optimises bandwidth consumption without compromising clarity. With these enhancements, VCX-IP ensures that delays, jitter, or signal impairments do not compromise ATM voice services, offering a robust and future-proof solution for critical ATM communications.

Echo-free communication and side tone feedback for controllers 

Voice clarity is critical in ATM, where misunderstandings or misinterpretations can lead to safety risks. A key factor influencing usability is side tone, which provides controllers with real-time feedback on their transmissions. Without effective side tone management, controllers may experience echo, self-hearing, or uncertainty in their transmissions, leading to potential confusion or communication errors. Frequentis has optimised side tone functionality within VCX-IP, ensuring that controllers receive instantaneous audio feedback without interference. Over-the-air loop detection confirms successful transmission, enhancing situational awareness and operator confidence. Additionally, the main/standby switching mechanism allows immediate failover between primary and backup channels, ensuring continuous operation in case of network degradation. The local side tone in VCX-IP is dependent on transmission confirmation, preventing unintended feedback loops and improving overall communication reliability. These optimisations contribute to reduced communication errors, increased safety, and improved controller efficiency.

Application-aware voice routing and best signal selection 

ATM voice communications require uninterrupted service availability, even in heterogeneous or degraded network conditions. Traditional fixed-routing voice systems cannot dynamically adapt to network impairments, leading to potential voice dropouts, delays, or packet loss in the event of congestion or link failures. VCX-IP introduces intelligent, application-aware voice routing that ensures calls are always transmitted over the best-performing network. Real-time monitoring continuously assesses network conditions, enabling dynamic path selection to prioritise the lowest-latency and highest-quality routes. Best signal selection dynamically evaluates available network paths and chooses the optimal route based on real-time performance metrics such as latency, jitter, and packet loss. This ensures that voice communications remain clear and uninterrupted, even in high-latency environments such as satellite-based ATM networks. Automated failover mechanisms seamlessly reroute traffic in case of link degradation, maintaining operational continuity.

Seamless voice integration across ATM networks 

Frequentis VCX-IP, fully compliant with ED-137, provides a scalable and interoperable voice communication solution designed for modern ATM networks. It ensures seamless operation between legacy and IP-based voice infrastructures, allowing ANSPs to modernise their networks step-by-step while maintaining high levels of safety and performance. With its ability to dynamically compensate for network fluctuations, mitigate latency, and enhance voice clarity, VCX-IP delivers a reliable and future-ready solution for air traffic management voice communications. By integrating advanced voice optimisation techniques, Frequentis ensures that ANSPs can maintain clear, reliable, and high-performance voice communications, even in complex, multi-network ATM environments. With robust delay compensation, echo-free side tones, and best signal selection, VCX-IP enhances controller-to-pilot communications, ensuring safety and efficiency in global ATM operations.