On Cisco AS5350 there are total 4 ports from 3/0:D to 3/3:D. But sometimes Cisco sends 'ISDN 0/-1:D:0' in NAS-Port-Name attribute. It seems there are more such calls at the time when the traffic is stronger. At this time there is smaller number of active calls than number of call attempts like for some reason some call attempts hang. E.g. in dead night I can see 0 active calls and 4-5 call attempts. I resolve it by shutting down/up E1 controller from time to time. I wonder what could be the reason? I'm using c5350-is-mz.123-1a.bin IOS.