Concurrency
Concurrency, in telephony, is the number of calls a line, phone system or service can carry at the same time. A call that arrives when every channel is in use gets a busy signal, a queue or an overflow destination.
Also called: concurrent calls, simultaneous calls, call capacity
A single traditional line carries one call. A SIP trunk is sold by channels, each channel one simultaneous call. A hosted service has a concurrency limit per account, sometimes per plan. The question "how many calls can you handle at once?" is a question about concurrency.
For a human team, concurrency is bounded by headcount: five people answer at most five calls. Automated systems are bounded by what the provider allows and by the capacity behind the number. What happens at the limit, busy tone, hold music, overflow, is a design decision worth checking, because it is what a caller experiences at the busiest moment of the day.
Related
aiReceptionist does this: Concurrent calls supported