If your agents on a queue use to transfer calls out to other callers or to other queues, you may notice that this is not reported correctly by QueueMetrics. You may also notice that if you use agent channels, an agent stays idle after the transfer until the transferred call is over.

Unfortunately this is "by design"; this is because when you use the Attended transfer button on the agent's phone, the main PBX is not notified that the call is "handed-over", so it still thinks it's connected to the original agent. The official documentation says that "transfers performed by SIP UA's by way of a reinvite may not always be caught by Asterisk [...] The only way to be 100% sure that you will get this event when a transfer is performed by a queue member is to use the built-in transfer functionality of Asterisk".

So the only way there is to handle this case is then to use so-called "Unattended transfer", that is, setting the t option in the queue and then having your agent press # to start a transfer to a different extension. Unfortunately, this does not give you Attended transfer, that is, speaking to the receiver before handing over the call.

Our real-life workaround is to use the "#" unattended transfers of Asterisk to transfer calls only after having opened up a parallel conversation to negotiate with the receiver. We know it's sub-optimal, but this has been shown to work.