How does the PSTN-E1-Asterisk communication work

Hi guys, my first time here, and thanks for this great forum where members can help out each other!

I just need some explanation on how the PSTN to Asterisk communication works. I have an Asterisk system connected to the outside world (PSTN) using an E1-line. I use a dual-span Digium card where only one span is connected to this E1-line through a modem. As I understood this far, I can receive 30 concurrent calls to the Asterisk system from clients through the PSTN.

Here comes my doubts: What happens if there are more than 30 clients calling my DID simultaneously? Will the telco forward them to the Asterisk system anyway, or will clients just get busy tones? The intention is to keep those who are not directly connected when dialing my DID in a queue until there are channels free to connect them. Is there any chance?

Thank you!

You have 30 channels, so if the 30 channels are in use then the telco will likely send back a busy tone. Any “keeping in a queue” would need to happen on the telco side.

And the PSTN is similarly limited between exchanges, and is typically dimensioned such that the bottleneck is the part between exchanges, so they would not want to provide such a queuing facility.

Calls in the backbone, are identified by their slot number in the trunk, so you can’t have signalling to say that a call is waiting a free slot.

Grateful for the quick replies! Thank you both!

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