Calls from our 3cx to a customer 3cx fail on transfer

[JJ_EIT]

The situation is that if we call just one of our 3cx customers, the phone rings fine and is able to be picked up. However, when someone on the other end attempts to transfer us to another user, we then start to hear our own 'On hold' music. If I watch the customers 3cx dashboard I see this as an example:

My call > Initial receiver (100)

Initial receiver (100) --- Transfers --> Ext (101)

Ext 100 starts flashing red and then they pick up the call but it says 'Engaged'

On our end however, all we hear the moment the transfer starts is our hold music. And then when we see the transfer complete in the dashboard, we're never connected. It just keeps playing our hold music.

We tested this with a mobile phone and the transfer works fine if we call the customer through any other means. It is only when we use our 3cx system it does this. Anyone have any ideas on where to start troubleshooting this? I'm assuming its the customer system as we don't have this with other customers but would like a penny for your thoughts.

 

[Kevin Attard Compagno]

Let's clarify the call flow. Is it:

Ext.200 on 3CX_01 calls external number
Incoming call on 3CX_02 from external number answered by Ext.100
Ext.100 on 3CX_02 transfers to Ext.101 on 3CX_02
Ext.200 on 3CX_01 hears hold music

?

If this is the scenario, your first step is to do a SIP capture on both systems for the call, and then start digging

 

[JJ_EIT]

Hi Kevin, thanks for the reply. Yes that's what's happening, but what Ext.200 on 3CX_01 is hearing is its own hold music/message, not the client's. And then when the call does get picked up by Ext.101 on 3CX_02 the call just doesn't ever complete the connection.

I'll do a SIP capture like you recommended Thanks

 

[leejor]

Do both of you happen to use the same provider?
If so, Is this provider supported?
Are you able to try a call using a different route (provider) to see if the behavior is different?

 

[Kevin Attard Compagno]

So basically 3CX_01 thinks that Ext.200 needs to be put on hold, which is indeed part of the flow in an "attended transfer" scenario.

This is practically 100% a SIP signaling issue.

Out of curiosity, can you check if a pure BLIND transfer just works? The SIP exchanges are fewer and simpler for BLIND transfer...