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

ED-137 Test Solutions

GL’s MAPS™ ED-137 address the need for additional testing needs that may include emulating many endpoints and generating bulk calls (load testing) on the network. GL offers (Message Automation & Protocol Emulation) MAPS™, a software platform, which can emulate 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 emulation 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 emulate AG/GG call recording towards Recorder and testing Recorder interface of CWP/VCS and GRS in ATM network.

Solutions for Air Traffic Management

Solution Architecture Components

GL's TM-ATM solution combines specialized hardware and software components to capture, timestamp, correlate, and analyze signaling, control, and voice events across Air Traffic Management networks.

GL’s solutions include rack-mounted and portable hardware equipment deployed across the Air Traffic Management network.

• Central Administrative System:
• Controls all the components of TM-ATM test suite and runs the tests to perform measurements
• Calculates the time difference between posted events and reports the precise one-way delay at different points in the network
• ED-137 Radio Emulator:
• Emulates Air-Ground calls (as per ED-137), and multiple CWPs or GRSs
• Can emulate PTT/Squelch, send and record audio to perform end-to-end voice delay and quality measurement
• Emulates all radio events such as Main/Standby Tx Rx switching, Mute/Unmute Receiver etc.
• Packet Filter System:
• Deployed in-line on an Ethernet network
• Provides 32 hardware filters to filter and timestamp the packets of interest at wirespeed
• Packet filtering can be based on Layer 2 (Ethernet), Layer 3 (IP), and Layer 4 (UDP/TCP) headers
• Can generate TTL triggers (1 Microsecond pulse) for each filter passed
• Analog VCS/Radio Emulator:
• Emulates PTT/Squelch and Audio; generates TTL triggers based on PTT On, PTT Off, Audio Start and Audio Detect (On or Off)
• Inject and record analog signals at the VCS and Radio
• Event Decoder:
• Receives filtered packets from Packet Filter System and Control Signal Detector with timestamping
• Processes received packets, sends notifications to the Controller Administrative System
• Detects audio in RTP packets to identify the beginning of voice in the stream
• Control Signal Detector:
• Monitors IO channels of the Sensoray for low-to-high and high-to-low transitions
• Used to filter and forward desired events/frames
• Monitors TTL output from the Analog Radio Controller and Packet Filter System and generates a corresponding IP packet to send to the Event Decoder
• Voice Quality Testing Software:
• Performs end-to-end voice quality assessment using industry standard ITU algorithms (PESQ and POLQA) across the ATM network

Emulating and Analyzing Air Traffic Voice Sessions

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 emulates 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.

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