I'm somewhat under the impression that if there is a complete communication failure, a message will display on the keypad, but I'm not 100% certain if this is true. In my case, nothing displayed. However, that also doesn't tell me if it kept retrying if it failed and over what period of time.
True, a complete comm failure will result in a comm failure trouble. So maybe your message finally got through after 18 minutes of trying?
I checked back in my log to when I had my router failure. the daily test was at 9 am. The "fail to communicate" trouble was logged at 9:18 AM. At the time I had two phone numbers, and I think it was configured to retry each number for 8 times, so that would have been 16 dial attempts. Maybe the Elk takes a full minute to time out on a failed dial attempt? That seems poor. Hopefully Spanky will comment here or in my "Best Practices for CS notification, Elk M1, NextAlarm, UpLink" thread
http://www.cocoontech.com/index.php?showtopic=12497