We recently did a lighthouse deployment with a very old PBX, the Avaya Definity G3r. There were a couple minor complications to this configuration however we were able to get through it with no issues and have full call flow between the two systems. I wanted to share the configurations we implemented in case anyone else runs into this unique PBX scenario.
Again we were utilizing a dialogic DMG2120 gateway for this implementation, if you notice on the Dialogic interoperability site you will not see any guides for the Definity G3 and OCS. http://www.dialogic.com/microsoftuc/pbx_integration.htm
We noticed in the exchange UM portion they had information for CAS signaling, however we could not get the CAS signaling to work properly so we decided to go with a T1 ISDN connection. The PBX would not support the QSIG standard so I reached out to our local support channel for some guides with the NI2 ISDN protocol. Dialogic does not currently have any official documentation around this setup, however they were able to provide some basic screens for me to hand off to the Avaya admin, and you can see these configurations below: (Note: These configuration screenshots were provided by Dialogic, I did not produce these)
Those screens above will get your Avaya side ready to handle the NI2 signaling from the dialogic gateway. The Dialogic side of this configuration is very basic and can be found below:
This customer also was one of the customers requiring #9 to get out to the PSTN which you can find a fix to in my previous post here.