Good day!
Is it possible to bind call limit of outbound to trunks or SIP?
On my setup. I’ve tried to set “call-limit=1” on my extension. It worked, I can process call 1 at a time. The only problem is I cannot transfer my call to other extension.
Assuming extension really means peer and the transfers are native attended transfers (but note some devices use attended transfers even for blind ones), when a SIP device does an attended transfer, it appears as a new, unrelated, call to Asterisk, so will trigger any limit on the number of sessions with that peer.
You can use any criterion to define your group. You do explicitly assign a channel to a group. You could even make it time-dependent or depend on the whether, provided you get get this info into Asterisk (which is not that difficult). The beauty of GROUP is not really the setup, but that you can later get the counts with very little effort and then decide what to do.
I don’t think the OP means extensions in the Asterisk sense, even though they said “yes” to the question, as they said device extensions, and there is no such concept.
I suspect you want to limit calls from devices not from extensions. An extension in Asterisk is something that appears in extensions.conf.
When SIP devices make native attended transfers the call starts out indistinguishable from a second line call from the device, so it is not possible to accept those but reject second line calls.
Quite a few SIP phone products actually use the attended transfer protocol when making blind transfers. They implement an automated half attended transfer.