Cannot hear transfer - Cause: 503 Transport failure

[Phill.]

Hi,

I have noticed that every so often, when an external party calls in and is transferred, the receiving agent cannot hear the remote party, but the line still shows as connected on the phone.
We use Yealink devices setup as remote stun, with the latest supported firmware, individualized SIP and RTP ports with PBX delivering audio for calls. I have also enabled extensions to accept multiple calls.

Here is the error:

08/07/2018 12:45:53 PM - Call to T:Extn:2004@[Dev:sip:2004@<myipaddress>:6643] from L:80.1[Line:10000<<anonymous] failed, cause: Cause: 503 Transport failure: no transports left to try/INVITE from local
08/07/2018 12:45:53 PM - [CM503003]: Call(C:80): Call to <sip:[email protected]:5060> has failed; Cause: 503 Transport failure: no transports left to try/INVITE from local

I have looked around but cannot find anything that looks to help with this type of issue. Could anyone provide any insights?

 

[YiannisH_3CX]

Hello @Phill.

Can you describe the call flow the call follows when this happens? For example is the call arriving directly an extension, a ring group or a Queue? Then is it transferred to an extension directly?
Is it a blind or attended transfer?
Also are all extensions remote Stun extensions behind the same public IP? If so is the option "PBX delivers audio" enabled under all extensions?

 

[Phill.]

Hi @YiannisH_3CX - thank you for your reply.

The external caller comes into a queue where the first agent picks up the call. There is then an attended transfer to another remote stun extension, using the same public IP. Yes the option "PBX delivers audio" is already enabled under all extensions.

 

[craigreilly]

I believe this is usually a transport error - TCP vs UDP. Can't say I know the fix though except to ensure the extension is setup properly. You do not mention how the devices are setup and if they are supported or not.

 

[Phill.]

Hi @craigreilly

I am using a mix of Yealink t42g, t42s, T46 models with the latest firmware - 28.83.0.20.

Let me know if there is there is anything else you need.

 

[YiannisH_3CX]

Is this a windows or linux server? Also is this a hosted instance? Do you have access to the instance?

 

[Phill.]

hi @YiannisH_3CX

it is hosted in Azure using the express PBX method to set it up (debian OS). Yes i have access to the instance.

 

[Phill.]

here is the state of the Azure network security group for the PBX instance

 

[YiannisH_3CX]

Please check your inbox as i have sent you a p.m. with what is needed to further troubleshoot this issue.