Wayne Farley's Aviation Blog - Air Traffic Management

ATS Message Handling System (AMHS) is the set of computing and communication resources implemented by ATS organizations to provide the ATS message handling service. AMHS is part of the ground-ground application of the Aeronautical Telecommunication Network which includes ATS Interfacility Data Communication (AIDC). AMHS is essentially the replacement of the Aeronautical Fixed Telecommunication Network (AFTN) which is based on very old technologies such as Telex (60+ years) and the relatively more recent X.25 (point-to-point communication)/CIDIN (Common ICAO Data Interchange Network). Industry support for X.25 is due to be phased out before the end of 2009 with all such systems becoming obsolete.
The new communications standard which have emerged is based on the X.400 world-wide messaging standards and on the Internet Protocol (IP) for transmission and routing. This has set the direction of the replacement but the new standards cannot simply be superimposed onto the existing networks. To enable co-existence of AMHS and AFTN, ICAO has also specified standards for interoperability between AMHS and AFTN, using a component formally referred to as an MTCU (Message Transfer & Conversion Unit) which provides a gateway between AMHS and AFTN. In Europe, a project called ECG (European or EATM Communications Gateway) was developed as the gateway between AFTN and AMHS in order to facilitate the transition from legacy protocols to this new standard.
Integral to the gateway is a directory, since AFTN addresses are different to AMHS addresses. The messaging gateways that connect AFTN and AMHS must translate between these different forms. The translation process depends on address translation data which must be globally synchronized.
The first AMHS system went into operational use in 1996 with 36 centers for the German Military and the first civil AMHS connection began operational use in February 2005 between the ANS Providers of Germany and Spain. In the Caribbean region, Jamaica was the first to install AMHS in 2007.

So why is AMHS necessary?
As pointed out earlier, the AFTN is an ageing technology which is very specialized; it is not based on modern standards, and has no market outside the ATS community. The market is therefore very small which means that the costs associated with AFTN supply and procurement are relatively high. Furthermore, because AFTN technology is based on the Telex protocols, it is limited to text only messages with a maximum length of 1800 characters.
AMHS, on the other hand, has a much higher functionality (which includes Security and Directory access facilities), and the messages can carry any kind of digital information, including text, graphics, images, files, databases, audio and video.
So, whereas the AFTN technology is sufficient for the currently defined AFTN messages, AMHS can expand the type and functionality of messages to support a wider range of ATC messaging requirements within a standardized framework.