After 15min the external caller cannot hear us. But we can hear him.

[objectis]

Hello,

We've have an issue for 1 month with our phone SPA504G and SPA502G.

If we receive an external call, after 15 the external caller cannot hear us. But we can hear him.

So we need to hang up and call back them.

The issue do not come if we initiate the call to the external caller.

We've contacted the VOIP Provider. They scanned the network but they found nothing. So they told us that the issue could come from the Firewall.

A colleague who works in an other building has the same issue and her phone is not connected to the same Firewall.

So I don't think that issue come from the Firewall. Somebody has an idea to fix that ?

Thanks for your help

[Gregory Brunn]

Assuming you have a SIP trunk 1 way audio is normally the case of a routing issue or a firewall issue.

What is your firewall? Palto? Cisco? I would start by ensuring your SIP ALG is turned off.

[objectis]

Hi,

Thank you for your help.

Our firewall is a SonicWall TZ 100.

[Gregory Brunn]

SIP ALGs are called SIP Transformations in SonicWall.  Can you please post a screen shot showing that you have them turned off.

[Slavik Bialik]

According to what Gregory said, here's some document from SonicWall that you can use in order to understand where those settings located:
https://www.sonicwall.com/en-us/support/knowledge-base/170503552140480
If you have it enabled, please disable it.

[objectis]

Hello,

Thank you for your advice I was on holliday last week so I will try that this week and tell you if it fixes my issue.

[objectis]

Hi,

I've configured the Firewall like they explain on your link. But it doesn't work. Do you know if I need to restart the firewall after apply the changes ?

[objectis]

Hello,

I've connected the phone directly to the modem (the modem do not have firewall). And I've called the phone. After 15 minutes I had the same issue.

So someone has a suggest ?

[Gregory Brunn]

Time to take packet captures from both side and see what happens.

[objectis · Accepted solution]

Finally we've fixed the issue.

That came from the codec we use for the phone. We used before the codec 711u but we must configure it to 711a because we live in Europe.

Maybe that could help someone.