If this is what I’m thinking about, it is a feature of PABX hunt groups. Basically, there are three commonly used call distribution methods;
1. “Round Robin” – The first call is sent to extension 1, the second to extension 2 etc. If extension 2 in this example is busy when a call should be presented, the call goes to 3, and 2 misses this turn.
2. Strict order. Call 1 goes to extension 1, call 2 goes to extension1, but if busy goes to 2 etc. So, in this way, extension 1 always receives more calls than any other extension.
3. Longest free. Whichever extension has been free for the longest period of time gets the next call. Arguably, this system is a fairer method of call distribution.