[outages] [EXTERNAL] Re: IPAWS/FEMA National Test - VoWIFI

[Sean Donelan]

On Wed, 4 Oct 2023, Chapman, Brad (NBCUniversal) via Outages wrote:
> Are these alerts queued up for later delivery if a device is off-line, out of range, or connected to a Wi-Fi calling network (where these types of cellular signals are not relayed?)
>
> If so, how long are they stored before being purged from the system?  1 hour?  24 hours?

WEA/CMAS are not queued.  WEA/CMAS are re-broadcast by carrier towers 
multiple times during the valid time (determined by the sender) over 
the control channel.  In this case, the valid time was 30 minutes.

There is no record in the carrier network which devices received a WEA
broadcast.  If you turn your device (off and) on later, during the valid 
period, it may receive a tower re-broadcast (or not, radio waves are not 
deterministic).  Each WEA/CMAS messages have a carrier-specific short 
serial number.  The mobile device is responsible for detecting duplicate 
transmissions (using the short serial number), and not re-alerting for 
previous alerts.  In annoying situations, if your phone roams between 
different carriers, the carrier short serial numbers may not match 
causing duplicate alerts.

The alert cache is flushed when you turn you phone off, so it won't detect 
old duplicates when turned on again.


SMS Text are different.

SMS Text messages are queued in the carrier network, when you phone comes 
back online it makes a point-to-point data request for queued messages. 
The carrier keeps a log of SMS Texts, when & where sent, when & 
where received