Specifications

Configuring the SIP Registrar

Information About Configuring the SIP Registrar

Cisco Unified SIP SRST 4.0 System Administrator Guide

Information About Configuring the SIP Registrar

Cisco Unified SIP SRST provides backup to an external SIP proxy server by providing basic registrar

and redirect services. These services are used by a SIP IP phone in the event of a WAN connection outage

when the SIP phone is unable to communicate with its primary SIP proxy. The Cisco Unified SIP SRST

device also provides PSTN gateway access for placing and receiving PSTN calls.

To make maximum use of the Cisco Unified SIP SRST service, the local SIP IP phones should support

dual (concurrent) registration with both their primary SIP proxy or registrar and the Cisco Unified SIP

SRST backup registrar. Cisco Unified SIP SRST works for the following types of calls:

• Local SIP IP phone to local SIP phone, if the main proxy is unavailable.

• Additional services like class of restriction (COR) for local SIP IP phones to the outgoing PSTN.

For example, to block outgoing 1-900 numbers.

How to Configure the SIP Registrar

This section contains the following procedures:

• Configuring the SIP Registrar, page 24 (required)

• Configuring Backup Registrar Service to SIP Phones, page 26 (required)

• Configuring Backup Registrar Service to SIP Phones (Using Optional Commands), page 30

(optional)

• Verifying SIP Registrar Configuration, page 33 (optional)

• Verifying Proxy Dial-Peer Configuration, page 34 (optional)

Configuring the SIP Registrar

The local SIP gateway that becomes the SIP registrar acts as a backup SIP proxy or redirector and accepts

SIP Register messages from SIP phones. It becomes a location database of local SIP IP phones that are

set up for dual registration. Dual registration allows SIP IP phones to simultaneously register with both

their primary and their fallback registrar devices. That is, when a SIP IP phone registers with a Cisco

Unified SIP SRST gateway, it simultaneously registers with the main proxy and SIP redirect server for

coverage in case of a WAN failure.

A registrar accepts SIP Register requests and dynamically builds VoIP dial peers, allowing the Cisco IOS

voice gateway software to route calls to SIP phones.

If a SIP Register request has a Contact header that includes a DNS address, the Contact header is

resolved before the contact is added to the SIP registrar database. This is done because during a WAN

failure (and the resulting Cisco Unified SIP SRST functionality), DNS servers may not be available.

SIP registrar functionality is enabled with the following configuration. By default, Cisco Unified SIP

SRST is not enabled and cannot accept SIP Register messages. The following configuration must be set

up to accept incoming SIP Register messages.