One way audio when encryption used

[Ronan]

Hello,

this is most certainly a network issue but the network guys are stumped, so I'm looking for ideas I could suggest them.

E1 => 3300 MXe (media gateway) => ISS MiVB (user gateway) => 5330 phone

MXe and ISS are on the same site, same LAN. Phone in on a distant site, through a WAN

5330 calls other phones in the network : OK
Other phones in the network call 5330 : OK
5330 calls the world through the E1 : OK
world calls 5330 : one way audio, the 5330 ears, but the world gets nothing.

I tried switching off compression, so from G729 to G711, no difference.

I tried switching off voice encryption on both mivbs : problem "solved", that way audio is fine in all cases. However, I can't leave it that way, I need to encrypt calls.

There are a couple firewalls between the user gateway and the phone.

there are more than 1500 other phones on the same user gateway but on other sites, on the LAN or various WAN links, that work fine.

I see UDP packets from the phone to the media gateway even when there is no sound, suggesting the packets are being corrupted somehow. Nothing untoward in voice quality statistics.

Any idea appreciated.

Regards

[Tom2018]

Hi Ronan,

how are the phones connected? via VPN?


regards,

[Ronan]

The WAN link is an MPLS VPN.

[Tom2018]

And the required ports are all open?
Maybe a SIP-ALG on any router is active...

[Ronan]

Thanks for the suggestion, I'll pass it along.

We have provided the list of ports to open (from Mitel documentation), I'm fairly confident it's good on the LAN side, however on the WAN side it's a third party so we can't be sure and are building a case that the problem comes from them.