Abstract

Although established some 60 years ago voice communications is still the sole means to separate and guide aircrafts. Voice communication systems are therefore amongst the most critical installations in air traffic control (ATC). Frequentis was the first to introduce PCM (pulse code modulated) based equipment for ATC worldwide and is on the leading edge of steering into the world of packetized voice communications. VoIP is the emerging voice communication technology which has already proven to provide satisfactory service for commercial applications. However, in ATC a number of requirements exceeding commercial applications have to be met. The voice communication system for ATC integrates radio communication as a prime service. Delays generated by the system therefore directly affect the performance on the radio channel and need to be extremly low. Both the radio control (push-to-talk, PTT) and the voice content need to be processed and delivered in a timely manner. SIP (session initiated protocol) based signalling represents a promising approach to tackle the delay problem. In addition, voice communication systems are required to provide high availability figures. VoIP based systems strongly rely on the communications infrastructure as they are distributed by nature. Resilient packet ring structures allow for these high availablity figures for the communications infrastructure.