What is the difference between publisher and subscriber in CUCM?

• A. Publisher is the primary database/administration node; subscribers replicate the database and handle call processing.
• B. Publisher handles call processing; subscribers replicate the database but do not process calls.
• C. Subscribers are the primary database; publisher replicates data for call processing.
• D. Both are equal; differences are only in licensing.

Answer: (A)

In a CUCM cluster, the key idea is that one node acts as the central administrator with the master database, while other nodes function as replicas that also process calls. The publisher stores the authoritative CUCM database and is where all configuration changes are made. It then propagates those changes to the other nodes. The subscriber servers maintain copies of that database and carry out call processing for devices registered to them. This setup provides centralized control plus distributed processing and redundancy. If you tried to assign call processing to the publisher alone or treat all nodes as equal in terms of data authority, you’d lose the clear master/replica relationship that CUCM uses for consistency and fault tolerance.