CAP EAS/NWR Profile

From CAP Cookbook

A key characteristic of the Common Alerting Protocol (CAP) is that it can be used to include and extend existing warning technologies as part of a larger integrated public alert and warning system.

The two most widely deployed public alerting systems in the U.S. at present are the broadcast-based Emergency Alert System (EAS) and the VHF National Weather Radio (NWR) network operated by NOAA. Both of these systems use the Specific Area Message Encoding (SAME) data format for automatic triggering of audio broadcasts. While CAP is not limited to the very low-speed transmission scheme used in SAME, and therefore can provide even more precise targeting and more detailed description of alerts, it frequently is useful to include the data from a SAME "data header" within a CAP XML message.

There are several possible approaches to including the SAME data within the CAP message structure. One obvious method is to include the entire SAME data string within a <parameter> structure. This method is simple, but has the disadvantage of not putting geospatial and topical information in the appropriate sections of the CAP message. This dislocation can lead to ambiguities and lost information, especially in more complex (e.g., multi-targeted or multi-phased) CAP messages.

The approach used in the "Digital EAS" trials conducted in early 2005 by the Department of Homeland Security placed the elements of the SAME header in their corresponding locations within the CAP 1.0 message:

• The EAS geographic codes, based on FIPS county codes, are included in CAP <geocode> elements within an <area> structure, under the type "same"; e.g.:" <geocode>same=006037</geocode>". (It is desirable but not currently mandatory that the targeted areas also be described in <polygon> form for the benefit of non-SAME-based recipients.)

• The EAS event code is included in the CAP <info> structure in an <eventCode> element of type "same", e.g.: "<eventCode>same=CAE</eventCode>" for an AMBER alert.

• The EAS expiration value is converted into the XML dateTime format and included in the CAP <expires> element.

• The EAS sender identification is presented in the CAP <source> element within the top-level <alert> block.

• Optionally, the EAS originator-category code may be included in the <info> block as a <parameter> of type "same", as in: "<parameter>same=CIV</parameter>". (If this field is omitted the default value of "CIV" is assumed, indicating that the message came from a civil authority.)

• A CAP <resource> structure includes a <uri> element indicating where a digital audio recording of the message may be retrieved. (At some point in the future text-to-speech technology may make this unnecessary, but for now it's effectively mandatory for activating EAS.) In one-way "datacast" environments a <derefUri> element is used instead and the base-64 encoded audio file becomes part of the CAP message itself.

• The text of the EAS audio message can be assembled from the text of the <audience>, <senderName>, <description> and <instruction> elements.

While some of the specific tag names and element structures will change in CAP 1.1, this general approach has proven to integrate well both with EAS and NWR equipment and with other alerting systems.