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Collaboration, Voice & AV · Intermediate

Inbound Calling Search Space

The CSS assigned to a CUCM gateway or trunk that determines which partitions incoming calls from that device can reach.

Definition

Calls arriving from the PSTN or another system are routed using the gateway's or trunk's CSS. Restricting it to only DID-related translation patterns protects against toll fraud by preventing external callers from reaching PSTN route patterns and hairpinning out. Getting it wrong is a common cause of inbound calls failing with a reorder tone.

Example

The CUBE trunk CSS contains only PT-DID-Translations, which maps DIDs to internal extensions.

Exam tip

If inbound calls fail but outbound work, check the trunk's inbound CSS and incoming digit manipulation.

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