What describes the purpose of partitions and CSS in CUCM?

• A. Partitions are number/route namespaces; CSS defines what partitions a device/user can search.
• B. Partitions manage user accounts; CSS handles call recording.
• C. Partitions map to QoS policies; CSS selects codecs.
• D. Partitions store dialed digits; CSS controls trunk settings.

Answer: (A)

The key idea is how CUCM dial plan controls who can reach what. Partitions act as namespaces for numbers and route patterns, effectively grouping DNs and routes into separate “folders” in the dial plan. The Calling Search Space (CSS) is a filter assigned to devices or users that defines exactly which partitions they are allowed to search when dialing. When a caller dials a number, CUCM looks at the matching route patterns and checks whether their CSS includes the partition that contains that pattern. If it does, the call can be routed; if not, it’s blocked. This combination is what enforces who can reach which destinations and helps prevent unauthorized or unintended calls. The other options mix up responsibilities—user accounts, call recording, QoS, codecs, stored digits, or trunk settings aren’t what partitions and CSS manage.