Critical Wireless Communications and
Weather Information Systems

Implementing the ED-137 Interoperability Standard

Until a few years ago, TDM networks were the default choice for Air Traffic Management (ATM) voice communications, and for ATM data serial connectivity was used. Today, these legacy networks are being phased out, and a migration to Voice over Internet Protocol (VoIP) and converged IP networks is in process. Organizations such as the International Civil Aviation Organization (ICAO), the European Organization for Civil Aviation Equipment (EUROCAE), Single European SkATM Research (SESAR) project and the NextGen program of the Federal Aviation Administration (FAA) have defined guidelines on how to accomplish the transition to IP-based networks.

Aeronautical voice communications or “Voice ATM” communications include all voice applications used for the purposes of Air Traffic Management (air-ground communications, co-ordination and transfer, emergency, Search and Rescue, flow management, capacity planning), ATM voice covers intra- and inter- center (all types of ATSUs: ACC, APP, TWR, MIL, NMOC) communications and also ensures the connectivity between the centers and the ground radio based stations on the ground leg of the Air-Ground communications between controllers and pilots. Thus, it is a very unique and “critical” type of communications and as such it has to operate according to very high standards of reliability, robustness and interoperability.

Why Voice ATM is Unique

Voice ATM cannot be handled the same way as non-aviation use communications. We have all heard that in commercial wired and wireless communications there are several industry accepted voice compression protocols such as algorithms such as G.711, G.722, G.729 etc.

In addition, those of us that have worked in the radio communications industry for some time have become accustomed to the implementation of various radio over IP modes such as DMR, IDAS, MotoTRBO, Nexedge, P25 and Tetra.

These may work well for ground-only communications but when it comes to ground-air communications they don’t fulfill the need. One of the main reasons for this is that regular two-way radio RoIP or VoIP don’t consider is interoperability. ED-137 compliant systems must be interoperable regardless of the manufacturer or the type of equipment. Thus, an ED-137B compliant voice switch (VCS) from manufacturer A has to be compliant with an ED-137B VHF radio from manufacturer B. There are several other aspects that ED-137 considers as well such as:

  • Quality of Service (QoS)
  • Supervision
  • Security
  • Allowing aviation specific modes such as CLIMAX (requires Time Stamping)
  • PTT (Push-to-Talk)

How Morcom Can Help You

Morcom distributes the CRU995 Gateway. This device has multiple applications: It can be used to connect legacy systems to new ED-137 compliant IP systems. Like for example, a legacy VCS that uses E&M type connections can be connected to ED-137 IP-type radio transmitters and receivers. And viceversa, an IP-type VCS can be connected to legacy analog radios. The CRU995 is an excellent tool to help you migrate to a fully digital VoIP system in a gradual fashion without having to discard fully functional equipment.

What follows is a detailed explanation on how the CRU995 can help you fulfill specific applications:

Case 1 - Using Legacy VCS and Legacy VHF Radios

Figure 1 shows how you can use two CRU995 units to connect a legacy (analog E&M VCS) to four legacy (analog) VHF radio transceivers. Notice that the connection between the two CRU995’s is made via IP LAN and can be any distance (based on your network).

Case 2 - Connection of a Legacy VCS to ED-137 VHF Radios

Figure 2 illustrates how you can use your legacy VCS with analog 4 Wire E&M interfaces and connect it to four ED-137 VHF radio transceivers (or transmitters and receivers).

This type of application requires the use of a single CRU995 and allows you to extend the life of your VCS while being able to modernize your radio equipment.

Case 3 - Connection of a Digital VCS to Legacy Radios

This application is the opposite of the previous one. Here you have a modern ED-137 VCS switch, but you still want to use analog radios. Please refer to Figure 3. It shows an application where the voice switch (VCS) is digital ED-137 VoIP and needs to be connected to analog radio transceivers or transmitters/receivers that use 4 wire E&M signaling. A single CRU995 can accomplish the task.

Case 4 - Full ED-137 Digital Network

Figure 4 depicts a fully digital ED-137 network. As you can see the digital VCS is directly connected to digital ED-137 compliant radios. No CRU995 is needed in this case, but if you still have a portion of your system operating in analog for the CRU995 could easily be used to those elements to the digital network.

For more information call us at 1-800-683-4101 or contact us through the request form.

Please click HERE to go to our VoIP Gateway page

MORCOM 21-Jan-2019 2 Comments


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αποφραξεις commented on 23-Mar-2020 11:31 AM5 out of 5 stars
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Eric Belrose commented on 24-Nov-2020 10:32 AM3 out of 5 stars
Good Afternoon:

I am researching ED137B/C compliant voice communications solutions, and I was wondering if you have any paperwork that I can read up on, such as product comparisons and technical characteristics. I am not making any procurement decisions, though I am interested especially in small portable systems that are perhaps mobile or rugged, and can handle 8 radios and support legacy interface with 2 operator/supervisor positions.

If you have any information I would gladly read.


Eric Belrose

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Chantilly, VA 20151, USA

Phone: (703) 263-9305
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