Cisco VOIP ISDN Backups For SIP

[Curiosityx]

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 for the SIP trunk, 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:

Main CLID

0121 872 0211

DDI's

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.

Regards

 

[#Chri5#]

Does your SIP provider to offer a fall back service if they see / detect you being off liine (ie SIP Registration time-out)? At this point, they could divert to the ISDN which will have a different number range.

 

[Curiosityx]

Indeed ive done some digging and can see that it's a feature that needs to be supported by the ISP, you have answered my questions in regards to what happens when the SIP Trunks fails in regards to whether the number is redirected onto the ISDN line or a new number is used and redirected by the ISP.