Customer reports that when the WAN link fails calls to PSTN get dropped because ISDN PRI drops and reassoicates with SRST.
Souldn't there be a seemless failover to SRST for calls incomming/outgoing to PSTN
I'm assuming your gateway is using MGCP. If so, this is expected behavior. During normal operation, an MGCP PRI backhauls the D channel to Callmanager. When the WAN goes down, so does the D channel. When the D channel drops, so do your calls. It then has to reestablish the D channel with the local gateway. Take a look at the following link.
Hope this helps.