Enhanced Voice Recorder Emulator for VoIP Air Traffic Control

17th, Jan 2020

Welcome to our latest issue of GL Communications' newsletter providing information and insight into our enhanced ED-137 Voice Recorder Emulator referred to as MAPS™ ED-137 Recorder Emulator to support volume 4 recording.


Air traffic control centers are required to provide continuous "ground/ground" and "ground/air" voice communication recordings with synchronized flight related data, for establishing “air traffic incident” chronology, replay, safety improvement, audits, statistics, and training purposes.

ED-137 defines inter-operability standards for the next generation VoIP Air Traffic Recorder. These next generation recorders are specially designed for all traffic control towers and centers to simplify the recording, archiving, and playback of voice communications.

VoIP Air Traffic Control

The latest release adds important new enhancements to MAPS™ ED-137 Recorder Emulator as per ED137-4C Volume 4 Recorder version. These include:

  • Provides option to simulate both ED137-4B and ED137-4C versions of Recorder Interface
  • Recording 2-byte base R2S header and R2S header extensions (R2S-TLV)

    R2S operation values are sent with RECORD and PAUSE messages for PTT/SQUELCH. 16 bit R2S header contains PTT, SQU, PTT-Id, PTT Mute, PTT Summation etc. R2S-TLV value carries extended headers like Climax Time Delay, Signal Quality Index etc in Type, Length and Value format.
  • Recording Client supports RTSP session keep alive
    Recording Client assures RTSP session keep alive by sending RTSP GET_PARAMETER request periodically to Recording Server.
  • Recorder Call Flow

    Recorder Call Flow

  • Checking Recorder Server liveliness by sending RTSP OPTIONS requests

    Server Liveliness will check whether the Server is available or not to process and respond to the RTSP requests. While GET_PARAMETER is used within the RTSP session and RTSP OPTIONS requests is used outside the active RTSP session to check the availability of the server.
  • Simulates Caller Rejected calls, Attended Call Transfer, Joining Conference
    • Caller Rejected calls event allows the caller to reject the call before sending SETUP or TEARDOWN messages.
    • Attended Call Transfer event is used to simulate Attended Call Transfer on Ground-to-Ground calls, which requires minimum 2 users to be configured with proper Called Number (User 2 is considered as third-party number). Example scenario would be ‘User A’ calling ‘User B’ and B transferring the call to C.
    • Joining Conference event is used to simulate the conference call. Join Conference option is used to add a user to the conference and Exit Conference allows to remove the user from the conference call.
  • Simulates proprietary Call Record Details (CRD) metadata
  • All SIP requests and responses will have WG67-Version header updated with Recorder version 'recorder.02'
  • Supports unicast recording sessions, where the SSRC assigned by Recorder Server is used for media stream
  • Additional call properties are added - Call Type, Client Type, Client Id and Disconnect Reason

For comprehensive information on the application, please visit our MAPS™ ED-137 Recorder Emulator web page.

Back to Newsletter Index Page Back to Newsletter Index Page