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Collaboration, Voice & AV · Foundational

SIP Registrar

A SIP server that accepts REGISTER requests and binds a user's address of record to the device's current contact address.

Definition

When a SIP phone boots it sends REGISTER to the registrar, which stores the mapping between the address of record (for example sip:1001@example.com) and the contact IP and port. Proxies use this location service to route incoming calls. Registrations have an expiry and must be refreshed; CUCM acts as the registrar for its SIP phones.

Example

A Cisco 7800 phone sends REGISTER to CUCM every few minutes, and CUCM responds 200 OK.

Exam tip

If phones show unregistered, check REGISTER/200 OK exchanges, TFTP configuration and CUCM group membership.

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