How Much Data in CAP?

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Now that the IPAWS OPEN server is on-line, it makes sense to get your CAP-enabled EAS equipment going. It's quite likely that your EAS system location already has Internet access; if not, it must by the end of June. But what if your only choices for Internet access are slow or limited in cumulative data over the course of a month? For an efficient system, make sure the polling you do is simply for the short update message. That message will include:

1. A unique ID
2. A link to the entire message
3. A time stamp
4. A list of states affected
5. The EAS event code

Your EAS device should use its configuration to determine whether or not it wants to download/use entire messages. Assuming the short update length is 250 bytes, and you poll for updates twice per minute, you would have: 250 x 2 x 60 x 24 x 30 = 21.6MB total data (for a 30-day month). If you wanted to download the audio from the RWT, add in another 4MB (since the audio for the RWT will be around 1MB, four times per month) for a grand total of 25.6MB per month. Thanks to Harold Price of Sage for this information.

Irwin is transmission systems supervisor for Clear Channel NYC and chief engineer of WKTU, New York. Contact him at

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