Dropped outgoing calls when calling specific carrier's mobile numbers with VoLTE enabled

[digrivas]

Hi,

One of our customers who has Freepbx 14.0.13.26 with Asterisk 13.22.0 installed, started having dropped outgoing calls just after they dial the number with only one out of three of our mobile carriers. When this happens they get the message “The number is not answering” and on the remote phone a missed call appears.

After many hours of research and information collection, we have a rough picture of the infrastructure involved:

FreePBX → SIP Trunk to TELCO → GENBAND Infrastructure → Mobile Carrier → VoLTE

TELCO says that the issue started just when the Mobile Carrier put VoLTE into operation because it needs the FreePBX to support the SIP UPDATE method which apparently does not. They also insist that due to their GENBAND infrastructure the cannot intercept the UPDATE request and manipulate it.

They send us a SIP trace to prove that FreePBX does not “Allow” the update method (see attachment).

So, our question are:

1. Can we do something in order for the UPDATE method to appear in the Allow line (maybe an adjustment or even a version upgrade)?
2. Is the line drop normal?
3. Is this a bad implementation scenario from Mobile Carrier’s or TELCO’s side?

Thanks

[billsimon]

@digrivas

Can we do something in order for the UPDATE method to appear in the Allow line (maybe an adjustment or even a version upgrade)?

My outbound invites with PJSIP allow UPDATE:

Allow: OPTIONS, REGISTER, SUBSCRIBE, NOTIFY, PUBLISH, INVITE, ACK, BYE, CANCEL, UPDATE, PRACK, REFER, MESSAGE

Changing to a PJSIP trunk might be your simple solution.

[digrivas]

Ok, thanks. Will try that and get back to you.

Anyone else about my other questions 2 & 3?