Testing ED-137 and ED-138 Interoperability Standards for VoIP Air Traffic Control

Critical Delay Measurements using Audio Analyzer & Packet Analyzer

Measuring delay, jitter and packet loss through air traffic networks is crucial and network testers must precisely time events. Delay testing and verification will be particularly important with the transition to IP networks, which will introduce packetization delays, jitter buffer delays and other uncertainties. For example, measuring the time from which the Air Traffic Controller presses ‘Push To Talk’ to the time when the IP packet indicates that the PTT bit is set to 1 is an essential testing scenario. This delay measurement is possible using GL’s Audio Analyzer as well as GL’s Packet Analyzer.

For more details, please visit Critical Delay Measurements in Air Traffic Management webpage.

ED-137 Test Solutions

GL’s MAPS™ ED-137 address the need for additional testing needs that may include simulating many endpoints and generating bulk calls (load testing) on the network. GL offers (Message Automation & Protocol Simulation) MAPS™, a software platform, which can simulate both Air-Ground calls (as per ED137_1B and ED137_1C: Radio) and Ground-Ground (as per ED137_2B and ED137_2C: Telephone) calls as per EUROCAE (European Organization for Civil Aviation Equipment) ED-137 standards. MAPS™ ED-137 support can emulate many user agents (end points) without requiring analog interfaces.

The software also supports simulation of Recorder interface for both Air-to-Ground and Ground-to-Ground calls at CWP, GRS and Recorder endpoints as per ED137_4B and ED137_4C versions. Air Traffic Recorder is the next generation VoIP recorder implemented as per ED-137 inter-operability standards. Specially designed for all traffic control towers and centers to simplify the recording, archiving, and playback voice communications. It can simulate AG/GG call recording towards Recorder and testing Recorder interface of CWP/VCS and GRS in ATM network.

MAPS™ ED137 can be used to set up voice sessions over a network, then send and record test voice signals for assessing voice quality and performance. It simulates both Controller Working Position and Radio Media Gateway System, with following important features required to maintain reliable communication over air traffic network.

• RTP Extended Header
  Supports RTP header extension format as per extended header type 0x167 (WG67). Both audio RTP and R2S packet will carry this 8 byte extended header. PTT and Squelch fields are set properly to signal voice activity in uplink or downlink. PTT-id assigned by remote end will be reflected in extended header.

• R2S-KeepAlive packets
  Supports generation of R2S-KeepAlive packets while there is no active voice being transmitted or received to keep the SIP session maintained. Push-To-Talk (PTT) and Squelch fields are reset properly to signal silence (idle period) in uplink and downlink respectively.

• Supports additional SDP parameters
  • R2S-Keep Alive Period: Maximum time (or frame interval) between each R2S-keep Alive packet. integer, in milliseconds.
  • R2S-Keep Alive Multiplier: Number of Keep Alive packets in error or not received by endpoint before Time Out of the session
  • PTT ID: PTT identity (value from 000001 to max. number of possible RTP streams, e.g.111111=63) assigned to each user agent by GRS endpoint in 200OK response to INVITE.
  • Version of the used RTP HE (Header Extension).
  • Frequency Identity.

• Supports Additional SIP headers 'Priority' and 'Subject’.
  Every INVITE contains these two headers.

• Priority: normal (Indicates SIP call priority)
• Subject: radio (Indicates SIP call type)

• IP Spoofing
  Supports IP address spoofing to generate each SIP call using different IP address from a single system.

For more details on MAPS™ ED-137, please visit MAPS™ ED-137 Telephone , MAPS™ ED-137 Radio, MAPS™ ED-137 Recorder webpages.

WAN IP Link Simulation using GL’s IPNetSim™

Voice Quality Testing (VQT)

ATM Network Quality Monitoring Tools per ED-138

Resources

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