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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