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fall back to ISDN from SIP trunk in cause of SIP trunk failure

Mujeeb Shaik

in case I have a ISDN connection and as well as a SIP connection terminating on our CUBE/Voice gateway. In case of the SIP connection goes down, the client wants the calls be automatically routed via your ISDN line


how should i achieve this

4 Replies 4

Gregory Brunn


Can't you just accomplish this via a dial-peer preference statement.


Preference 1 sip trunk


Preference 2 ISDN PRI pots dial peer





Mohammed al Baqari
VIP Advisor VIP Advisor
VIP Advisor

You can do this using options ping which will switch the call directly to
isdn dial peer instead of waiting for sip invites timeout.

Here you go

***** please remember to rate useful posts

Roger Kallberg
VIP Expert VIP Expert
VIP Expert

Apart from the advice already given, it’s of importants that you’re client understands that you only have control of this for outbound calls. For inbound calls from PSTN it’s the service provider that controls this and it’s not very likely that they would have the ability to route the calls primarily via SIP and use the ISDN as backup. It’s at least nothing I’ve ever came across.

Response Signature

In addition to all the comments I also suggest reducing the SIP timers and retries under sip-ua.  This is to prevent excessive delay is the SIP service goes down, before the Options Ping polling shuts down the dial peer.  Default timers/retries would have it trying for something like 30 seconds.  I normally use two retries and a reasonably short timer, the exact figure would depend on how quickly your provider normally responds.  Remember the timer doubles on each retry, so this example would timeout after 1.75 seconds ..

 retry invite 2
 timers trying 250
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