Press Release : GL Announces
Timing Measurement Tools for Air Traffic Management System

Gaithersburg, Maryland, USA – June 20, 2016 - GL Communications Inc., announced today Timing Measurement Tools for Next Generation Air Traffic Management (ATM) Networks.

Speaking to press, Mr. Jagdish Vadalia, a Senior Manager for Product Development of the company said, “The latest European Organization for Civil Aviation Equipment (EUROCAE) ED-137 inter-operability standards, address migration and implementation of IP based technology for voice services for air traffic control. The familiar industry standard SIP protocol is specified to establish, modify, and terminate voice sessions with endpoint equipment within an Air Traffic Services Ground Voice Network (AGVN).  As shown in the first main network diagram, the endpoint equipment can be a SIP based Controller Working Position (CWPs), Next Generation Voice Communication Systems (VCS) and Radios, or VCS/Radio Gateways allowing interworking with older legacy equipment and protocols. The legacy TDM VCS system will initially connect to an IP WAN network backbone using VoIP gateways.”

He added, “Though migrating to an IP network provides convergence advantages for traffic and interoperable network elements from various vendors, it also poses challenges – of variability of different implementations by equipment vendors. Some of these are: implementation of technologies with varied jitter buffer, packetization, digital signal processing algorithms, VOX operations, and switching from idle to active state.  These implementation differences impact end-to-end delay requirements imposed by various industry standard bodies. Characterizing and limiting these impairments is critical to the performance of the system as a whole. Rigorous methods are needed to precisely measure the delay introduced by each network element as events propagate end-to-end.  Recognizing, capturing, timestamping, and correlating events at analog, TDM and IP interfaces are necessary.  Delay measurements should be conducted repeatedly to ensure that the device and network under test is performing as expected consistently over time.  

GL has developed a suite of tools to accurately simulate and measure all delay requirements. GL’s MAPS™ Controller can be used to control the various GL tools to perform all the tests repeatedly 1000s of times and record the results for post analysis. Events of Interest within Network as they propagate within Network are:

PTT Activation and Deactivation, Squelch Enable and Disable, Voice to/from CWP, Voice to/from Radio, Transition in RTP Payload, Transition in RTP Headers.  And Network Delay measurements of interest are: Transmitter activation delay, Aircraft call indication delay, Ground transmission voice delay, Transmitter activation and aircraft call indication loopback delay , Ground reception voice delay, Ground transmission and reception voice loopback delay, Frequency key activation response time and more.  To perform several of these timing measurements, one can setup a testbed with appropriate AVN elements and various GL tools at appropriate strategic interfaces. GL’s script based and API driven products can be reused for various purposes during performing various test cycles.

Mr. Vadalia further explained, “The time from which an Air Traffic Controller depresses the PTT until the IP stream indicates that the PTT bit is set - is an important testing example. This delay measurement is possible using GL’s Audio Analyzer and GL’s Packet Analyzer. Both are capable of generating TTL triggers based on PTT activation. The Packet Analyzer is capable of generating Packet and TTL triggers based on real time packet detection, filtering, and capture as necessary.

As provided in the above second network diagram, a remotely located MAPS™ Controller can instruct GL’s Audio Analyzer connected to a CWP to activate PTT and simultaneously generate a TTL trigger.  The Discrete Signal Logger connected to the Audio Analyzer can detect the TTL trigger and post an event to the Event Data Logger. On the IP side, GL’s Packet Analyzer which is monitoring the line non-intrusively can detect the packets of interest (e.g.first RTP packet with PTT bit set) based on the filters set and post an event to Event Data Logger. Centrally located the Event Data Logger time tags these received events and reports these events to the MAPS™ Controller. The MAPS™ Controller will calculate the time difference between different events posted and reports the measured delay.

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