Greetings, previous to the current project im working on ive only ever used either ISDN or SIP for inbound and outbound call connectivity.
The current prospect im looking at is a single site which will be using SIP as the primary VOIP transport, SDSL for Data and ISDN as a backup, configuration of this setup isnt a problem but there is one issue i haven't thought of before.
For example a block of DDI's will be assigned to the incomming SIP trunk's. In this scenario lets say they are the following:
0121 872 0211
0121 872 0212
0121 872 0213
0121 872 0214
0121 872 0215
0121 872 0216
0121 872 0217
Could someone let me know how i would achieve fault tolerance using an ISDN connection should the WAN connection drop by continuing to allow for incomming calls using the existing DDI range as of course the SIP trunk and ISDN connection are two seperate entities.