Technical bandwidth requirements for Emergency Alerts

Some background information for network engineers unfamilar with emergency alerts.

In the United States, there are approximately 500,000 emergency alerts nationwide a year, not counting another million or so test alerts. Only about 7,500 emergency alerts are severe enough to activate public warning systems. Most emergency alerts are intended for other emergency management agencies and officials. The rest are advisories, watches, updates and cancels.

The peak emergency alert busy day is 4 alerts per minute nationwide. Although stress testing indicates most emergency alert systems should be able to handle more.

Emergency alerts are not evenly distributed across the country. Some geographic areas have nearly none. Other geographic areas have many, e.g. tornado alley and atlantic coastlines.

Since the 1950s, there has never been an actual nationwide emergency alert, i.e. presidential alert message. Emergency alerts are almost all state, local and weather alerts. Test alerts are the most common alert type.

The IPAWS system supports very geo-targetted alerts, and supports opting in or opting out of specific types of alerts. When government officials use those options, and alert distributions implement those options.

When the IPAWS emergency alert standards were being written, 1.5 Mbps DSL lines and even 128Kbps ISDN lines were still common, so the IPAWS emergency alert message sizes were made relatively small. But it was still an huge improvement over the previous EAS radio and TV broadcast modem data bursts from the 1980s/1990s, which were limited to 256 characters.

The average IPAWS emergency alert is 5KB to 15KB in size. Including audio and image files, the entire emergency alert can be about 5MB in size.

In the U.S., audio and image files are transmitted separately because rural Internet connections were too slow at the time. Canada's AlertReady system is more recent, and can handle larger alert messages.
In Canada, audio and image files are transmitted as part of the satellite IP multicast emergency alert message.

The small 90-character cellular phone message was also due to the limited bandwidth available in cellular networks at the time. Newer cell broadcast networks can handle nearly 1,000 character messages. Starting in May 2019, the U.S. WEA mobile alerts will increase to 360 characters. Changes are slow.

It takes less than 10 seconds to transmit an IPAWS emergency alert nationwide. Although radio and TV may delay transmitting an emergency alert up to 15 minutes, i.e. during commercial breaks. The goal for earthquake alert messages is less than 3 seconds, which is not currently achievable.

All 500,000 emergency alerts do not need to be transmitted nationwide. An alert distributor can selectively transmits only relevant alerts to different geographic areas, and choose not to include less severe advisories or many tests.

Training for state and local government officials issuing alerts is very underfunded, and they make mistakes.

The public hates emergency alert systems, until a tornado destroys their home in the middle of the night, and then they complain they didn't get an emergency alert.