"The key to Digital Networking is that all of the Cisco Unity servers access a common directory. To use Digital Networking, the Cisco Unity servers must be in the same Active Directory forest." - Networking Guide for Cisco Unity Release 5.x (With Microsoft Exchange)
I want to setup a digital networking with the exististing setup. Currently, I have a lab system that run AD/DC/EXCH1/Unity1, how do I add another unity system to the existing setup to archieve digital networking? should I join the new server (will be hosting exch2/unity2) as a "member server" or as "an additional domain" or does it matter at all?
Shouldn't matter, just a little bit different installation process.
If you join the second Unity server to the domain as a member server, you will need to join the existing Exchange organization when installing Exchange since an Organization exists already.
If you add it as a new domain, you'll need to create a new Exchange Organization and make sure that you have a DC/GC in place for that domain (can be the Unity server providing you're meet the system requirements)
Hope that helps,