[VoiceOps] "Timeout" on VoIP call traversing Verizon data

[Dovid Bender]

If I had to guess Verizon is using CGNAT and since there is no traffic for
X amount of time the NAT hole for the SIP traffic is closed. When you send
a re-invite at the 30 minute mark that session as far as Verizon's CGNAT
devices are concerned have been closed a long time ago. You would need to
send a packet to the phone or have the phone send to your switch some sort
of traffic (we send SIP OPTIONS every 49 seconds) to ensure that the
session stays alive.



On Wed, Jun 9, 2021 at 3:27 PM Mark Wiles <mwiles at akabis.com> wrote:

> If there’s a Verizon cellular data guru monitoring here, I’d love to get
> your insight!
>
>
>
> Otherwise, let me toss this out to the group for thoughts and opinions
> please…
>
>
>
> We’re a Metaswitch shop, and use their MaX UC mobile softphone client
> (iPhone/Android).
>
>
>
> We had a customer using the MaX UC client on a long call… they were using
> Verizon cellular data (confirmed by IP address).
>
> At thirty (30) minutes into the call, the call “dropped”.  The call was
> re-established, and again, after thirty minutes, the call dropped.
>
> We’re pretty sure the user was in a static position (non-mobile)… and
> logically *assume* they were on the same cell tower for both calls that
> dropped (the Verizon IP was the same).
>
>
>
> Looking at Metaswitch SAS (their diagnostics tool), at the thirty minute
> mark, we send out a re-INVITE message to the softphone client… and we
> receive no reply… so after ten seconds, we breakdown the call assuming
> they’re gone.  Then about eight seconds later, we see an INVITE message
> from the softphone’s same IP address (with the same Call ID)… however, it’s
> coming from a different port.  So to be clear, the original call setup and
> connection was using 1.2.3.4:6789… then eight seconds after we ended the
> call with a BYE (assuming they were gone due to lack of reply), we get an
> INVITE (with the same Call ID) from 1.2.3.4:9876.
>
>
>
> Metaswitch looked at the diags from the softphone (we downloaded them),
> and they’re confirming that the softphone never received our re-INVITE at
> the 30 minute mark.
>
>
>
> Metaswitch also looked at the bug/crash logs on the softphone, and
> confirmed neither was the case.
>
>
>
> It almost sounds like a NAT thing going on… but I’m pretty ignorant when
> it comes to cellular data.  It looks to me as if the Verizon side simply
> changed port numbers, and assumed we’d know maybe via mental telepathy?
> 😊
>
>
>
> Has anyone had experience with such an occurrence… or any thoughts?
>
>
>
> Thank you!
>
>
>
> Mark
>
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