There was an outage this morning in my area related to the CO having issues. I found out when I got my alarms and realized that the PRI was not registering with CCM (over WAN link).
I did not have a whole lot of time to troubleshoot and react so my first reaction was to enable SRST by actually denying access to the MPLS router.
This, seemed to work. I was able to call in the office and not get the "this number has been disconected..." message. I was also able to put my IPC in that location and call out.
However, I just wonder how this would've work and I am not sure that it actually worked. It was early and I could not test with someone in that office. My IPC was enable through a VPN connection to the network so I wonder if this had an effect on the call out being succesfull.
I am still getting familiar with our config as I was not part of the dessing and came in in the middles of the implementation.
So the question is, wold SRST work even if the phisical PRI link is down? This connection was flapping. Perhaps some channels were still up, or perhas there is a config in the router that makes this work but I am not sure.
Your input will be greatly appreciated.
rvincent is correct. SRST will only become active if it looses it connection to Call Manager. If the PRI goes down depending on how your route list are setup in CM it will roll to the next available member in the list. So you will need POTS just like rvincent has mentioned as a backup to the PRI and include them into the route list for this site. That way if the PRI goes down it will roll to the next member which will be the POTS lines.
PRI will have no bearing on SRST going active. When your phones can not register with call mgr's they will register with their assigned srst router and this will enable the srst feature.
You need some pots lines to use as pri backup to keep outgoing service running when pri goes down.