[AusNOG] Telstra wifi calling issues

[John Edwards]

Hi James,

WiFi Calling uses the same backend as VoLTE.

With the 3G network switch off, VoLTE has required some tweaks recently to
ensure that 000 emergency calls still work as expected when a device is out
of coverage with its Mobile provider, but within the coverage of another.

This is because 3G gives a circuit out of the box, but Voice on an LTE
network requires establishing a data connection with an unknown party first
before a Voice call can be overlaid on it. Normally telcos don't just allow
data sessions to subscribers they don't know, and at the time the session
is established the intent for it to be an emergency call isn't known.

If the problems started occurring around the same time 3G switched off then
you may have found a place to start looking for a fault - there was almost
certainly a software or config upgrade to voice systems.

Trivia: The standard for LTE emergency call functionality was developed by
Huawei for Australia's TPG Telecom in their Singapore rollout, the 2nd
LTE-only mobile network globally, after Reliance Jio in India (I may have
heard they used an app-based approach to solve emergency calling)

John


On Thu, 28 Nov 2024 at 18:37, James Andrewartha <trs80 at ucc.gu.uwa.edu.au>
wrote:

> Hi,
>
> The past month or so some of our staff (whose desks don't get good Telstra
> coverage) have been complaining about calls going straight to voicemail
> when wifi calling is enabled (which we suggested due to the coverage
> issues).
>
> Doing a packet capture, I can see the IPsec tunnel being established to
> epdg.epc.mnc001.mcc505.pub.3gppnetwork.org. Some of the users have public
> IPs, others are behind NAT.
>
> Does anyone have any tips on working out why they'd be having issues all
> of a sudden?
>
> Thanks,
>
> --
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