IP/VoIP Protocol Simulators

Core Network Simulators

MAPS™ ED-137 Radio Emulator

Air-to-Ground Calls Simulation

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MAPS™ ED-137 Radio Emulator


Recent advances in Air Traffic Management over IP network has opened up both opportunities for providing better services, and challenges to ensure reliability, and performance. Among many other solutions for testing Air Traffic Control network, GL offers MAPS™ ED-137 Radio which can simulate Air-Ground calls (as per EUROCAE ED137_1B: Radio, and ED137_1C: Radio) calls.

MAPS™ ED-137 Radio simulates the functions of Controller Working Position (CWP) and Ground Radio Station – GRS (or Radio Media Gateway - RMG) entities in Air-to-Ground radio calls. The product supports transmission and detection of various RTP audio traffic such as real-time audio, voice file, digits, single tone and dual tones. The MAPS™ profile editor feature allows users to easily configure multiple CWPs and GRS profiles, allowing to simulate multiple CWP and GRS entities. Each simulated radio will have similar capabilities and its own set of parameters like Contact address, Radio type, Frequency-Id, and Permitted user list which can be configured in the profiles.

Air Traffic Management MAPS™ ED-137 Radio

GL tools for signaling emulation and voice quality testing offer an end-to-end test solution for testing connections from the radio interfaces to the Controller Working Position (CWP). GL’s Air Traffic Management Solution also includes MAPS™ ED-137 Recorder Emulators and MAPS™ ED-137 Telephone Emulators.

GL also provides a GUI based PacketScan - All IP Traffic Analyzer for online capture and decode of the signaling in real time both during tests and as a stand-alone tracer for live systems.

GL™s MAPS™ ED-137B Radio Emulator Connects to Live Romasta Radio!

GL™s MAPS™ ED-137B Radio Emulator Connects to Live Romasta Radio

At the recently held World ATM Congress event in Madrid, Spain, the GL™s MAPS™ ED-137 Radio Emulator capability was showcased. It was connected to a Rohde & Schwarz radio located in Romania with the help of the Romanian Air Traffic Services Administration Staff (Romatsa). This radio is responsible for a certain sector of the Romanian airspace. The ED-137B connection was made, with the GL™s MAPS™ Radio emulator in ™RX Only™ mode. Any airplane communication (squelch break) from an airplane in that sector was heard by our tool. We were also monitoring this connection with GL™s PacketScan™ which was able to show (in real-time) all of the voice and packet characteristics of this connection. Visitors seemed particularly interested in the real time Waveform viewer and MOS/Jitter etc. value measurements.

Main Features

Signaling and Traffic Simulation

  • Fully integrated, complete test environment for Air Traffic Management
  • Supports testing CWP, VCS, GRS (or RMG), and VRS elements
  • Supports both ED-137B Volume 1 Radio and ED-137C Volume 1 Radio versions of Air-Ground call simulation
  • Support for Multiple Radio Simulation (up to 200 Radios) within single instance of the software
  • Supports hundreds of simultaneous calls and complete automation of bulk call generation with traffic
  • IP Address Spoofing to automatically generate virtual IP address for a NIC
  • Linked Session Management to group and identify all calls belonging to particular Radio
  • Supports transport over IPv4, IPv6, UDP and TCP
  • Depicts easy to understand call flow graphs of SIP message exchanges and message contents (SIP headers and SDP attributes)
  • Supports multiple Profiles (Users/End points) from single node
  • Allows to define DSCP (Differentiated Service Code Point) values for signaling and voice traffic
  • Validated against VOTER version BASELINE SPECIFICATION Volume 1 - GRS Radio ED-137/1C compliance and VOTER version BASELINE SPECIFICATION Volume 2 - VCS Radio ED137/1C compliance
  • Supports Separated GRS (Tx and Rx) and Combined GRS scenarios
  • Supports PTT Summation and Coupling PTT Summation modes
  • ED-137B Volume 1 Radio
    • Support for user-events that can be applied dynamically on an established call (Re-Invite, PTT Priority, Signal Quality Information (SQI), CLIMAX Time Delay, Receive Traffic, Delay Compensation messages (RMM and MAM), Radio Remote Control, Impairments, Play to Speaker, RTP Audio/R2S-Keepalives
    • Supports simulation of Dynamic Delay Compensation messages - Request for Measurement Message (RMM) and Measurement Answer Message (MAM)
    • Supports sending simultaneous squelch on selected multiple Radios
    • Sample script provided to perform automated periodic Push-To-Talk (PTT) and Squelch (SQU) operations on Air-to-Ground (A-G) calls.
    • Option to define multiple traffic profiles for simultaneous simulation of various traffic actions
    • Supports sending audio using microphone and playing audio to speaker on multiple sessions
  • ED-137C Volume 1 Radio
    • CWP and GRS nodes support Radio Receiver Multicast operation
    • Supports selective calling with SELCAL tone transmission
    • Simulates non-VoIP source PTT keying
    • WG67 KEY-IN event package includes frequency id (fid) parameter to inform the User Agent about the new Frequency ID (fid)
    • No disconnect of active sessions when GRS frequency id changes
    • Includes PTT type - Test PTT
    • All SIP requests and responses will have WG67-Version header updated to 'radio.02'


  • Send and receive live speech, pre-recorded speech files, digits and tones
  • Set impairments (Packet Loss, Packet Effects and Latency) in relevant profile in real time
  • Provides aggregated voice quality statistics such as MOS/R-Factor, packet loss, duplicate and out of sequence packets
  • Supports user-defined and automated traffic actions on the call
  • Supports all standard codecs, including G.711 (mu-Law and A-Law) and G.729


  • On field testing and troubleshooting by technicians
  • In-the-field installation, system configuration and commissioning
  • Functionality testing of nodes in next generation VoIP ATM
  • Load testing and background traffic generation
  • QoS monitoring - analyze calls for voice quality (MOS), packet loss, jitter, latency, etc.
  • Centralized monitoring of Air Traffic
  • Real-time and/or historical data analysis

Single End Terminal Simulation

Air-Ground call simulation (as per ED137_1B: Radio)

A typical ED-137 Radio Call between CWP and GRS entities in Air-to-Ground call at one of the peer-end is as shown below.

MAPS™ ED-137 Radio Normal PTT Call Flow

MAPS™ ED-137 Radio can be configured as CWP for placing calls, and can also be configured as GRS to receive calls, thus simulating outgoing and incoming messages in Air-to-Ground call. 

MAPS™ ED-137 Radio configured as GRS and CWP nodes in the network

MAPS™ ED-137 Radio configured as GRS and CWP nodes in the network

Once a call is established between the two terminals ‘KeepAlive’ messages are exchanged between the terminals. Many other Events can be applied at CWP/GRS on an ongoing call such as PTT priority handling, Send Re-Invites,, Apply Time Delay in msec, Start/Stop sending RTP Audio/R2S-Keepalives, Start/Stop Impairments, Receive Traffic (i.e. record to file, detect digits/tones), Update Signal Quality Information, Radio Remote Control signal, and Playback the call on PC speaker.

  • Supports Normal/emergency radio sessions, all PTT Types and Radio call types.
  • Supports all SIP Methods, Headers and mandatory/optional SDP attributes defined in ED-137/1B.
  • Easy to operate PTT on/off, SQUELCH on/off, PTT Summation on/off, PTT Mute on/off etc., on the session.
MAPS™ ED-137 Radio configured as GRS and CWP nodes in the network

MAPS™ ED-137 Radio configured
as GRS and CWP nodes in the network

MAPS™ ED-137 Radio configured as GRS and CWP nodes in the network

MAPS™ ED-137 Radio configured as GRS and CWP nodes in the network

Multiple Radio Simulation

Recent enhancement to MAPS™ ED-137 Radio allows user to simulate multiple Radios in a single instance of MAPS. User can simulate up to 200 Radios (with unique IP addresses) in one system and each simulated Radio will have its own set of parameters defined in XML based configuration files. Each simulated Radio is a logically separated Radio with similar capabilities.

Configuration of Radio Profiles

ED137_Radio_GRS_Profiles is an XML configuration file that includes a set of multiple sub-profiles. These files allow configuring multiple radios with unique set of parameters for each radio such as Contact address, Address of Record, RTP IP Address, Radio type, Frequency-ID, and Permitted user list. 

Multiple Radio Profile Configuration

Multiple Radio Profile Configuration

Colour codes are used to sort and group all related calls and make it easier to visually distinguish calls belonging to a particular Radio.

Sorting and Grouping Calls

Sorting and Grouping Calls

IP Spoofing

IP spoofing feature allows multiple CWPs/Radios to be simulated using unique IP address from a single system. User specified IP addresses in Profile will be created as virtual IP addresses on the NIC interface used by the system.

Linked Session Management

The Linked Session functionality provides to the GRS endpoint the opportunity to detect all SIP sessions coming from the same user but from different equipment (i.e. different IP Address) to guarantee higher service availability.

GRS can identify the calls coming with same User part in ‘From Address’ but with different IP/host address and with 'ls-pl' SDP parameter included within the SIP headers. It will treat the linked sessions as one single logical session to radio.

The linked session functionality enables the GRS endpoint to support handling of redundant connections between VCS endpoint and GRS endpoint for all types of connections.

Linked Session Management Scenario

Linked Session Management Scenario

Simulation of Dynamic Delay Compensation Messages
(RMM and MAM)

Enhanced MAPS™ ED-137B Radio adds Dynamic Delay Compensation as an additional feature in which specific RTP extension block used to introduce varying delay values at GRS in lab environment without actually making the real-time measurements.

Once the Air-to-Ground call is established, CWP can send Dynamic Delay Compensation messages such as RMM to GRS. GRS replies with MAM. Message for each RMM received.

MAPS™ uses only relative time to calculate delay. After receiving the MAM message from GRS, delay is calculated and displayed in the message sequence graph along with RMM and MAM messages, as shown in the below image.

MAPS™ CWP Sending RMM message
MAPS™ CWP Sending RMM message

Radio Receiver Multicast Operation

In Multicast mode operation, multiple CWPs can send request to have multicast session with GRS to receive multicast RTP packets from GRS. CWP sends an INVITE request with SDP body containing multicast group address and TTL value to GRS. The GRS which supports multicast will extract the multicast address from SDP body in INVITE and starts sending the R2S/RTP packets to this multicast address. CWPs will send Internet Group Management Protocol (IGMP) join request to join the group and start receiving the multicast RTP packets. The router or switch with multicast feature will manage the subscription to multicast group and forwards the RTP packets received from GRS to all members of the group.  The below image depicts the process.

MAPS™ CWP Sending start receiving the multicast RTP packets

Selective Calling (SELCAL) Tone Transmission

SELCAL is a signaling method used to alert the aircraft crew members selectively to an incoming message from a ground station. The CWP endpoints simulated by MAPS™ ED-137 Radio supports sending SELCAL tones to GRS using the SIP INFO method. SELCAL tone defined in CWP profile will be sent in the body of INFO message as shown in below image. GRS replies with ‘200 OK’ message to INFO request and sends Normal PTT_ON confirmation with PTT-ID=63 in RTP downstream header to CWP.

PTT-ID=63 is reserved for SELCAL tone transmission at GRS. PTT priorities are handled at GRS as per ED137C for this transmission
MAPS™ ED-137 Radio supports sending SELCAL tones to GRS

Simulates Non-VoIP Source PTT keying

GRS endpoints simulated by MAPS™ ED-137 Radio supports simulation of non-VoIP source PTT Keying. User can simply apply “Key non-VoIP PTT” event on the selected Radio call at GRS. This will trigger GRS to send Normal PTT_ON confirmation with configured PTT-Id (60, 61 or 62) in RTP downstream header to all CWPs indicating that PTT from a non-VoIP source is being transmitted at GRS. PTT-Ids 60, 61 and 62 are reserved for non-VoIP sources. The below image shows the non-VoIP source PTT ON/OFF confirmations on the call graph.

Non-VoIP source PTT ON/OFF Confirmations on the call graph

Separated GRS

A Separated GRS group is formed by one Transmitter and one or more Receivers, all configured with same frequency F1.

We can have one CWP connected to Transmitter(F1) and one or more CWPs connecting to a single Receiver (F1) or to multiple Receivers with same frequency F1

The following figure shows the emulation of Separated GRS.

Call Generation CWP

Call Generation CWP

Call Reception GRS

Call Reception GRS

Combined GRS

In case of Combined GRS (Tx + Rx), CWP establishes a RadioTxRx or Coupling session to a Transceiver. When PTT is keyed on this session Transceiver will loop back the received audio on the same session with PTT Type, PTT-Id set as received and Squelch bit on.

The following figure shows the emulation of Combined GRS.

Call Generation (CWP)

Call Generation (CWP)

Gall Reception (GRS)

Gall Reception (GRS)


MAPS™ ED-137 Radio Simulation MAPS™ ED-137 Telephone Simulation
  • Emulates Radio interfaces at Controller Working Position (CWP) or Ground Radio Station (GRS) endpoints as per ED-137/1B Compliance
  • Emulates Air to Ground Calls
  • Supports generation of Real-time Session Supervision (R2S)-KeepAlive Packets and RTP Header Extensions to carry Radio signaling information as per ED-137/1B standard
  • Supports Normal/emergency radio sessions, all PTT Types and Radio call types
    • PTT Call types-  Normal PTT On, Coupling PTT On, Priority PTT On, and Emergency PTT On
    • Radio Call types – Radio Idle, Rx Only, Radio Tx Rx, and Coupling
  • Supported events - PTT on/off, Transmit CLIMAX Time Delay, send Re-Invite, receive traffic, impair traffic, and Play back the call on speaker
  • Option to define radio frequency, radio maintenance mode and permitted users list
  • Call graphs notifying all the above listed events with timestamp
  • Supports optional Climax Time Delay, RSSI Signal Quality Index and Radio Remote Control header extension types
  • CWP and GRS support WG67 KEY-IN event package (i.e. Subscribe/Notify of established Radio sessions at GRS)
  • Emulates Telephone interface at CWP endpoints as per ED-137/2B Compliance
  • Emulates Ground to Ground Calls
  • Supports all SIP Methods, Headers and Mandatory /Optional SDP attributes as per ED-137/1B
  • Supported call types include –
    • Instantaneous Access (IA)
    • Priority Direct/Indirect Access (DA/IDA)
    • Routine Tactical Direct/Indirect Access
    • Routine Strategic Direct/Indirect Access
    • Routine General Purpose Direct/Indirect Access
    • Position Monitoring Call (Combined A/G and G/G, A/G only, and G/G only)
    • Supported events -send Re-Invite, send traffic, receive traffic, put active call on Hold, transfer call, impair traffic, and Play back the call on speaker



VoIP ATM Test Solutions

MAPS™ ED-137 Radio Emulator

Workshop 1 : MAPS™ ED-137 Radio Emulator

MAPS™ ED-137 Telephone Emulator

Workshop 2 : MAPS™ ED-137 Telephone Emulator

ED-137B Test Solutions

ED-137B Test Solutions

Testing VoIP Air-to-Ground Calls per ED-137C Radio

Testing VoIP Air-to-Ground Calls per ED-137C Radio

Enhanced Test Tools for ED-137B VoIP Air Traffic Control

Enhanced Test Tools for ED-137B VoIP Air Traffic Control

ED-137 VoIP Emulation and Analysis for Air Traffic Management

ED-137 VoIP Emulation and Analysis for Air Traffic Management