Viking W2000 to FXO to Asterisk to FXS to Phone

At our company we have two doorphones. The front one works flawlessly, you push the button, it rings the front desk (using two Aastra 57i phones) and they punch in the front door code and it opens the doors.

The rear doorbell is a bit more of a problem. It is set to ring an old analog cordless phone, that is connected to an FXS port. I can call the number just fine from a SIP phone, but somehow when it’s going from Analog to Digital to Analog again, it stops working.

Normally I would simply get a Aastra 57i CT or similar that has a cordless handset. Unfortunately I don’t currently have that option.

Is this set up even possible? Here are the important bit of the config.

exten => s,1,Answer()
exten => s,n,Set(CALLERID(name)=“Doorbell”)
exten => s,n,Set(CALLERID(num)=“Doorbell”)
exten => s,n,SIPAddHeader(Alert-Info: info=)
exten => s,n,Dial(SIP/1100&SIP/1101,10)
exten => s,n,Hangup()

exten => s,1,Answer()
exten => s,n,Set(CALLERID(name)=“RDoorbell”)
exten => s,n,Set(CALLERID(num)=“RDoorbell”)
;exten => s,n,SIPAddHeader(Alert-Info: info=)
exten => s,n,Dial(DAHDI/49,10)
exten => s,n,Hangup()

As you can see by the normal doorbell, it calls SIP extensions 1100 and 1101. The rear doorbell should ring DAHDI channel 49 which is the port that the phone is connected to.

Like I said, this extension can be called directly (extension 226 in this case) but I’ve tried it with that as well.

Any ideas, suggestions, need more info?