T2 · T2-R01
Partitions and calling search spaces
Learn it in 5 minutes
- A partition is a bucket of patterns.
- A calling search space is an ordered list of partitions.
- The phone, the line, and the trunk can each have a CSS.
- First match in that order wins.
- A pattern you cannot see is not a failed route. It is invisible.
Visual
What is going on
This is the CUCM dial plan's access control. Lobby phones should not see the PSTN partition. Emergency patterns are usually placed so that every CSS used by a phone can find them. Confirm the emergency design for your region rather than copying a lab CSS.
Confirm before relying. Confirm the analyzer name and menu for your CUCM version.
Worked example
A phone CSS lists Internal then PSTN. The user dials a ten-digit number that also exists as a shorter internal pattern. If the shorter pattern is in an earlier partition, it matches first.
Quiz
1. CUCM searches every partition and picks the longest match across all of them.
False. It walks the CSS in order.
Ecosystem
Sister pieces sit on the ecosystem page: the glossary, the mind map, the integration map, and the sibling labs.
- Partition — A group of patterns with the same reachability.
- CSS — An ordered list of partitions.
Config. Read the CSS on the device and on the line. Both can apply.
Troubleshooting. DNA, or the Dialed Number Analyzer when your version has it, shows the path. Confirm the tool name in your release.
Bridge. Webex Calling locations and routing are a different model. Do not paste CSS words onto a Calling location.
Mind map, sister technologies, and future hooks live on the ecosystem page.
Sources
Product screens move. Confirm the guide for your release before you change a live system.
Sources and go deeper
Opened 2026-10. A row marked confirm has no link, because that page was not verified.
- Cisco. Cisco Unified Communications Manager product support last checked 2026-10
- Cisco. System Configuration Guide for CUCM, Release 15 last checked 2026-10
- Cisco. Cisco Collaboration Preferred Architectures last checked 2026-10
- Cisco. Preferred Architecture for Cisco Collaboration 15, design overview (PDF) last checked 2026-10
- Protocol and ports. CUCM 15 TCP and UDP port usage last checked 2026-10
- Protocol and ports. IANA SIP parameters last checked 2026-10
- Community. Cisco Community, Collaboration knowledge base last checked 2026-10
- Wikipedia. Voice over IP (Wikipedia) last checked 2026-10
- Wikipedia. CUCM (Wikipedia disambiguation) last checked 2026-10
- Cisco. Collaboration 12 SRND book. confirm. The historical Collaboration 12 SRND path opened as a product listing, not the design book. Use the Preferred Architecture index, which was opened. last checked 2026-10
- Wikipedia. English Wikipedia article for Cisco Unified Communications Manager. confirm. That title returned HTTP 404. The CUCM disambiguation page is the Wikipedia page that opened. last checked 2026-10