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Collaboration, Voice & AV · Foundational

Calling Search Space (CSS)

An ordered list of partitions that a device or line is allowed to search when placing a call, controlling what it can dial.

Definition

CSSs are assigned to devices, lines, trunks, translation patterns and features such as call forward and AAR. When both line and device CSSs exist, CUCM combines them with the line CSS partitions first. Partition order in a CSS breaks ties only when two matched patterns are equally specific; otherwise closest match wins regardless of order.

Example

CSS-Lobby contains only PT-Internal and PT-Emergency, so the lobby phone can call extensions and 911 only.

Exam tip

Line CSS takes precedence for ties because its partitions come first; the line/device approach puts restrictions on the line and routing on the device.

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