[sbe-eas] National WEA and EAS test performance

[Sean Donelan]

FCC surveyed major cellular carriers about the performance of the national 
Wireless Emergency Alert system.  The lawyers at the FCC and lawyers at 
the carriers have been exchanging letters, talking past each other. I 
don’t know if they are intentionally misunderstanding each other.

WEA Part 10 and EAS Part 11 do not have any specific performance 
requirements. Just vague terms like immediately. Computer clocks at alert 
originators, FEMA IPAWS, cellular and broadcasters are not tightly 
synchronized.  While GPS and NTP can keep computer clocks with 
milliseconds, EAS and WEA timestamps usually vary 5 to 10 seconds. Recent 
changes to EAS allows up to 15 minutes clock skew for message validation 
windows.

So...

What was the end-to-end latency of the national WEA test?

What was the end-to-end latency of the national EAS test?

For an engineer, it’s a difficult question to answer precisely.  Roughly 
(95% confidence), it takes about 1 to 2 minutes for a national EAS or WEA 
alert end-to-end from FEMA to reach the public. Minimum: 36 seconds, 
Maximum: 30 minutes (never). Including encoding/decoding latency, but not 
including delays in FEMA systems or alert origination.


CAP XML MESSAGE (Mountain Time)
sent = 2021-08-11T12:20:01-06:00
effective = 2021-08-11T12:20:01-06:00
expires = 2021-08-11T12:50:01-06:00

CMAC XML MESSAGE (UTC)
CMAC_sent_date_time = 2021-08-11T18:20:01.000Z
CMAC_cap_sent_date_time = 2021-08-11T18:20:01.000Z
CMAC_expires_date_time = 2021-08-11T18:50:01Z

EAS MESSAGE (Eastern Time)
sent = 2021-08-11T14:20:00-04:00 rounded to minute
FEMA to PEP
decoded = 2021-08-11T14:20:46-04:00 from XMSR (PEP)
decoded = 2021-08-11T14:20:51-04:00 from WETA FM (LP-2)
decoded = 2021-08-11T14:20:54-04:00 from WTOP FM (LP-1)
relayed = 2021-08-11T14:21:02-04:00
EOM received = 2021-08-11T14:21:42-04:00

AT&T
Reference Point A:   Alert Originator
Reference Point B:   IPAWS Gateway
Reference Point C:   Combined CBE/CBC
Reference Point D.1: August 11, 2021 at 13:20:08 CDT
Reference Point D.2: August 11, 2021 at 13:20:48 CDT (+40 secs)
Reference Point D.3: August 11, 2021 at 13:20:48 CDT (+0.100 estimate)
Reference Point E:   August 11, 2021 at 13:20:49 CDT (+1.000 estimate)

Repetition: 30 times at 60 second intervals (30 minutes) (calculated)

T-Mobile
Reference Point A:   Alert Originator
Reference Point B:   IPAWS Gateway
Reference Point C:   Combined CBE/CBC
Reference Point D.1: August 11, 2021 at 14:20:06.806 EDT
Reference Point D.2: August 11, 2021 at 14:20:42.701 EDT (+35.895 secs)
Reference Point D.3: August 11, 2021 at 14:20:42.845 EDT (+0.144 estimate)
Reference Point E:   August 11, 2021 at 14:20:43.485 EDT (+0.640 to +1.000 
estimate)

Repetition: 6 times at 5 minute intervals (30 mins) (UMTS/4G/5G) 
(calculated),
             8 times at 4 minute intervals (32 mins) (GSM) (calculated)

Verizon
Mid-Atlantic:
Reference Point A:   Alert Originator
Reference Point B:   IPAWS Gateway
Reference Point C:   Combined CBE/CBC
Reference Point D.1: August 11, 2021 at 14:20:05.969 EDT
Reference Point D.2: August 11, 2021 at 14:21:01.738 EDT (+55.769 secs)
Reference Point D.3: August 11, 2021 at 14:21:01.739 EDT (+0.001 to 0.003 
estimate)
Reference Point E:   August 11, 2021 at 14:21:01.740 EDT (+milliseconds 
estimate)

Southwestern US:
Reference Point A:   Alert Originator
Reference Point B:   IPAWS Gateway
Reference Point C:   Combined CBE/CBC
Reference Point D.1: August 11, 2021 at 14:21:06.510 EDT
Reference Point D.2: Not reported separately (see mid-atlantic)
Reference Point D.3: Not reported separately (see mid-atlantic)
Reference Point E:   Not reported separately (see mid-atlantic)

Repetition: 1 time at 1 minute interval (1 min)


Reference points refer to the "Commercial Mobile Alert Service 
Architecture and Requirements."
https://www.npstc.org/documents/PMG-0035_Final_Recommendations_v0.6.pdf