pmcook said:
There are no lines. It is a PRI.
Although the issue appears to be solved, it is worth explaining how the system treats lines with a PRI. It might be a good reference for other people, too.
When a call is received on a PRI trunk, the CO sends the channel on which the call is coming in and the number that the caller dialled (called the Received Number). The system then checks whether there is a Target Line with the same Received Number. If so, the call is mapped onto that Target Line.
On Norstar, each channel of the PRI is represented by a line number. If your DTI is in the first slot of the KSU, the channels are represented by Line 001 through Line 023. The system automatically removes the appearance of these lines when the DTI is configured as PRI, but you can put them back on your set if you want to. They can be used to monitor the activity of the PRI: the indicator will be on when the line is in use and it will be off when line is free.
If you program these lines to "Appear & Ring", you will notice that they don't ring. When a call is mapped onto a Target Line, only that Target Line rings. This is because the system considers that it has answer the call and that it is transferring it to the Target Line. This explains why the AA couldn't answer Lines 001 through 023: they didn't ring.
There is one case where a line will actually ring. If there are no Target Line that match the Received Number, the call isn't mapped onto any Target Line. The call stays on the line on which it came in and the system routes it to the prime set.
By the way, this behaviour isn't specific to PRI. It also applies to any line described as "auto-answer" in the documentation: DID trunks, but also T1, E&M and loop start trunks that are configured with the "Answer Mode" set to "Auto".