[VoiceOps] IPAWS/FEMA National Test - VoWIFI

Wed Oct 4 19:33:28 EDT 2023

...huh.

https://cacm.acm.org/magazines/2021/10/255719-securing-the-wireless-emergency-alerts-system/fulltext

Guess it is delivered over a separate interface to the MME than SMS would be.

Kinda boggles the mind that "WEA over IMS" isn't a thing.

Perhaps it's an issue of scalability?  WEA messages over NAS presumably doesn't require that much overhead: MME sends the message out to all eNBs, who in turn I'd guess would just indiscriminately transmit it to all attached UEs.  More broadcast-y than unicast-y.  Whereas I guess an IMS-based solution would require the CSCF to enumerate all active registrations and then transmit a SIP message individually to each subscriber, one-by-one.

Still, the lack of at least some IP-based way of accomplishing this seems like a huge oversight, especially in an age where it seems like more people (especially in more rural areas) are more reliant on VoWiFi than ever before in order to have any use whatsoever of their mobile voice service while at home.

-- Nathan

-----Original Message-----
From: VoiceOps [mailto:voiceops-bounces at voiceops.org] On Behalf Of Nathan Anderson via VoiceOps
Sent: Wednesday, October 4, 2023 3:53 PM
To: voiceops at voiceops.org
Subject: Re: [VoiceOps] IPAWS/FEMA National Test - VoWIFI

Darn...it actually had occurred to me to test this very thing by forcing airplane mode and then enabling WiFi, but then spaced it and didn't manage to do that before the broadcast went out!

Assuming I'd actually managed to run the test, I was actually fully prepared to be surprised if I had NOT gotten the test broadcast while exclusively on WiFi Calling.  It seems bizarre to me to learn that WEAs are dependent on the same NAS CP messages that non-IP-based SMS over LTE is also dependent on...can this really be true??  This is strange because it would require that all mobile carriers continue to run and maintain a 2G core, since (as far as I know) SMS can only be encapsulated within LTE NAS by way of the SGs interface.  (Perhaps there is some separate interface over which WEA payloads specifically are sent to the MME?)

Some months ago -- but well after the 3G UMTS shutdown had taken place -- I found that my ability to use SMS on the AT&T network had suddenly broken in a weird way, and ONLY worked over WiFi.  Which was naturally a *wee* bit inconvenient.  After digging into it over a few days, I figured out that the SMS over IP (IMS) setting in my (non-5G) handset's baseband was disabled.  And apparently this setting is ignored when you are on VoWiFi, since IMS is literally the only way to deliver SMS over ePDG.  I enabled it & that fixed my problem with SMS over LTE.  I did some back-and-forth testing and every time I re-disabled that baseband setting, SMS over LTE broke again.  I took this all as a sign that AT&T was probably looking to retire their entire 2G/3G core, though admittedly I haven't tried forcing the same handset back to SMS-over-SGs since then in order to see if maybe this was just a temporary (yet prolonged) glitch on their side.

-- Nathan

-----Original Message-----
From: VoiceOps [mailto:voiceops-bounces at voiceops.org] On Behalf Of Jay R. Ashworth via VoiceOps
Sent: Wednesday, October 4, 2023 2:08 PM
To: jra
Cc: VoiceOps
Subject: Re: [VoiceOps] IPAWS/FEMA National Test - VoWIFI

I now have a counter report that the Cellular Control Channel necessary to get
these alerts to a cellphone *is not proxied by carrier WIFI-connect*, by design.

I'm familiar with his credentials, and I'll assume he knows what he's talking about,
cause *I* know what he's talking about, and he sounds like he's talking sense.  :-)

Thanks to everyone who responded.

If you *did* get an alert, *and you know you were not in range of ANY cell network*,
only WIFI proxy, that wasn't supposed to be possible and I would still like to hear
about that.

Cheers,
-- jr 'just zis guy, you know?' a

----- Original Message -----
> From: "Jay R. Ashworth via VoiceOps" <voiceops at voiceops.org>
> To: "VoiceOps" <voiceops at voiceops.org>
> Sent: Wednesday, October 4, 2023 3:25:04 PM
> Subject: [VoiceOps] IPAWS/FEMA National Test - VoWIFI

> I have a report from a usually reliable source that he did not receive today's
> IPAWS/CMAS/WEA test message, and he surmises this might be because his phone
> handset is forced to VoWIFI.  I have a number of other reports, mostly though
> not all, from the broadcast engineering community; nobody reported expecting
> a CMAS and not getting it, so that's not data here.
> 
> Is anyone on the list involved with the FEMA/IPAWS/CMAS link, or knows someone
> who is, and has a channel to clear this query up through?
> 
> I could be unsurprised to find that the carrier VoWIFI proxies missed out on
> proxying SMS Cell Broadcast, which I gather provides the underlying PHY for
> CMAS.
> 
> Cheers,
> -- jra
> 
> --
> Jay R. Ashworth                  Baylink                       jra at baylink.com
> Designer                     The Things I Think                       RFC 2100
> Ashworth & Associates       http://www.bcp38.info          2000 Land Rover DII
> St Petersburg FL USA      BCP38: Ask For It By Name!           +1 727 647 1274
> _______________________________________________
> VoiceOps mailing list
> VoiceOps at voiceops.org
> https://puck.nether.net/mailman/listinfo/voiceops

-- 
Jay R. Ashworth                  Baylink                       jra at baylink.com
Designer                     The Things I Think                       RFC 2100
Ashworth & Associates       http://www.bcp38.info          2000 Land Rover DII
St Petersburg FL USA      BCP38: Ask For It By Name!           +1 727 647 1274
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