E1 (ISDN) Failover between 2 E1 ports in same router

[campbell-john]

I have two Asterisk based VoIP servers and each has an E1 card installed. 

One is a primary and the other a secondary (standby).

I am in the UK and have 1 ISDN E1 line from BT giving us our incoming/outgoing calls.  At the moment this is hard wired to our primary however if there is a failure with the primary it's a manual shift to the secondary.  I would like to automate this.

I have been looking at dedicated E1 failover units but these are either very hard to come by or horrendously expensive

I've therefore just had a thought but would like some clarification from the Cisco forum as to whether this would work or not.

I have a Cisco 2901 with 2 WIC cards giving 4 E1 ports.  Is it possible to configure this to act as an E1 failover?

I'm not wanting to convert anything to IP, I want it all done with E1, so for example:

BT Line in goes to WIC port 1

WIC port 2 has primary

WIC port 3 has secondary

Primary and Secondary can both make outgoing via BT line however only port 2 is receiving incoming from BT, however if there is a loss of service on the primary all incoming from BT then routes automatically to WIC port 3

It all sounds plausible to me but as I said I don't want to do any conversion to IP as there is sensitive modem traffic and would like to minimise this as much as possible.

Any advice would be greatly appreciated

Thanks

[James Hawkins]

Hello,

What you describe is pretty simple to configure from a Cisco point of view.

To do this you would configure two dial peers each of which point to the same destination number bt with different preferences and destination ports. A basic sample configuration is shown below:

!

dial-peer voice 2 pots

destination pattern 1...

preference 1

voice-port 2

!

dial-peer voice 3 pots

destination pattern 1...

preference 2

voice-port 3

In the sample config each dial peer points to the destination pattern 1...

The dots are wild cards so the number range would be 1000 to 1999.

Dial peer 2 has the better preference and so will be used if available and will send calls out of port 2.

Dial peer 3 has the worse preference and so will only be used if dial peer 2 is fully utilized and another call arrives (this is not possible in your setup) or if the port used by dial peer 2 is down. 

In a real config the port numbers would likely be different and some extra commands would be needed but hopefully this would give you the basics of how this would work.

In this setup the Cisco router itself becomes a single point of failure so I am not sure that it improves things much over just having a single Asterisk server.

I am wondering whether it would be possible to wire both Asterisk servers to the BT PRI circuit and have the interface on the second server shut down.

The second server could then somehow monitor the first server and if it went down it could bring it's own ISDN card up. You could do this with Cisco routers using Embedded Event Manager and I am sure you could do something similar with Linux scripting.

Hope this helps and let us know how you finally solve this issue.

James

[Ayodeji Okanlawon]

If I understand you correctly, the issue is failover for inbound calls. There is no configuration that can help you here. BT routes calls and they determine which trunk calls arrive on. You should ask them what failover solution they have in place for your trunks.

[Gordon Ross]

Ayodeji is correct: For inbound calls there's nothing you can do, you need to speak to BT.

I'd also suggest making outbound calls round-robin between the two trunks. That way, you know your links are working all the time. No point in a back up link if it doesn't work when it's needed, is there?

GTG