I have a 2811 ISR with IOS version 12.4(24)T3. It has a 4-port FXO port in it. I'm using MGCP to communicate between the router and CallManager. Two of the ports are set to do PLAR. The ports on the router do not have any configurations on them other than a hookflash 500 command pushed by MGCP. On CM, the attendant DN has been set for two different numbers. One of the PLAR lines is connected to a site that is only a couple of miles away. The other PLAR site is farther away, in a different part of the county. Both connect through the same PSTN, but I'm given to understand that while the same group is in charge of each end of the line for the connection that is closer, a different group is in charge of the end of the line for the connection that is farther away. I am also given to understand that there is different equipment being used for that connection (what it is exactly, no one seems willing to talk about).
The issue is that when we go off hook at our end on either of the two lines, the phones ring at the far ends and we can carry on a conversation. When someone goes off hook at the closer of the two sites, our phones ring and we can carry on a conversation. But when someone goes off hook at the farther of the two sites, our phones do not ring. The people at the far site say they get ringback in their ears, but our phones do not ring. If, however, we say to the people on the far site, "pick up the line in 20 seconds", we can pick up our end of the line in 25 seconds and they'll be there. They'll say they heard ringback and we can carry on a conversation.
What muddles this some more is the fact that when we connect an analog phone to the line that isn't working for us, the analog phone rings several times and we can get two-way audio. The PSTN is saying that all they need to do is deliver ringing and audio and they're all done.
However, when we flip the two lines on our router, the trouble seems to follow the line, which would lead us to believe that the PSTN is doing something different on the two connections and our router doesn't like one of those things.
Further troubleshooting has shown that when someone goes off-hook at the far end of the line that does not work, we do not see the light go on at the FXO port on the router. Plus, if we do a "debug voice ccapi inout" on the router, we don't see any activity when someone goes off hook on the far side of the connection that does not work (we see a ton of activity when someone goes off-hook on the far side for the connection that IS working).
The PSTN says it has to be our router. We are pretty sure it can't be. Are we missing something?
