I have floated the idea of possibly using asterisk/app_rpt to update an existing linked system which currently covers multiple states. In discussing this some questions of architecture have come up so I'm posing them to the list below. Many if not most of our sites have no access to telecom facilities, can be inaccessible for about 4 months out of the year, and the temperature in the buildings can reach vast extremes. Currently we link over radio channels on the 440 band but are working to move to microwave t-1 links with t-1 radios in the ham band and channel banks splitting out the audio. What signaling can be done over the existing single channel links to interface with legacy systems and how can the app_rpt boxes in the system signal each other over these links to convey status and signaling information between them? How would you go about addressing the environmental concerns above or architecting around them? Thanks, Eric KG6KQT