Specification Format for AIS Binary Messages



Submitted for presentation at[1]: US HYDRO 2007, Norfolk, VA, 14-17 May 2007.

Specification Format for AIS Binary Messages

for Providing Hydrographic-related Information

Kurt Schwehr and Lee Alexander

Center for Coastal and Ocean Mapping – Joint Hydrographic Center

University of New Hampshire, Durham, NH

kurt@ccom.unh.edu

kurt@unh.edu

tel: 603-862-1159

Abstract: UNH has worked in conjunctionis working with the USCG and NOAA to use XML (Extensible Markup Language) to define binary messages for maritime-based AIS (Automatic Identification System). Theis draft specification format will enable hydrographic and maritime safety agencies to define message contents by providing a bit level description in XML (informally the "AIS Binary Message Decoder Ring"). This format improves the clarity of message specifications aiding both people defining the messages and software engineers implementing maritime systems.

The XML file specifies of the order, length, and type of fields following a subset of that used by the ITU-R.M.1371-1. To reduce issues with accidents and errors caused by miscommunication (e.g., the Mars Climate Orbiter loss in 1999), units are declared for the numerical values, along with the standard descriptions and notes. The specification is independent of programming language (e.g., can be implemented in C, C++, C#, Java, Python, etc.) to allow vendors to integrate the system into their individual design requirements. Along with the XML specification, the draft specification contains a reference implementation of an AIS XML to Python compiler written in Python that has been released as open source under the GNU General Public License (GPL) version 2. An XML schema and an additional program will provide validation of the XML message definitions. A XSLT style sheet produces reference documentation in ‘html’ format. Although the XML message definition file specifies the order, size, and type of the bit stream, it does not specify semantics or how binary messages should be presented on an ECDIS or other display device.

The Ainitial demonstration of this specification will be for sending tide/water level messages will be part of the Elizabeth River Demonstration Project at the US HYDRO 2007.

________________2007 U.S. Hydrographic Conference.

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[1] It is suggested that this be presented at a Poster Session.

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