A SIP registrar is a server in an SIP network that accepts SIP REGISTER requests. The SBC Edge SIP Registrar operates in two modes, owner and Proxy.
In the owner mode the SBC Edge is the owner of the Address Of Record (AOR) for each SIP device and is responsible for maintaining the bindings for each number, and the registrar responds to registration messages with a time to live value configured in the UI.
In the proxy mode the AOR is owned by another network device and the SBC Edge Registrar obtains the AOR information as a proxy. Registration messages are sent to the SBC Edge which is responsible to forward the message to the AOR owner, bindings are maintained by the network device with the SBC Edge acting only as a relay point. In order to force the endpoint to register at regular and reasonable intervals when the network device becomes unavailable or has been restarted, the SBC Edge modifies the bindings and reduces the time-to-live values. The proxy mode allows the SBC Edge to obtain routing information while not requiring security credentials to be configured for each endpoint.If AOR is not a local domain the registration can be forwarded to Server Host. Contact information in responses will be retained in registrar.
The SBC Edge can be configured in in three SIP Modes: Basic Call, Forward Registration after Local Processing, and Local Registrar. Basic Call mode has no registrar functionality and therefore, registration functionality applies to only the last two modes.
The figure below illustrates how registration is processed in the Forward After Local Processing mode.
Under normal circumstances, when a device registers with the SBC Edge its information is captured in the local registrar and then forwarded to the SIP server for registration and the SIP server is responsible for all call bindings.
If an Outbound Proxy is specified in the SIP Signaling Group, it takes precedence over the SIP Server. Therefore, proxy registration is moot.
When Forward After Registration is the selected SIP mode and the SIP server becomes unavailable, the local registrar maintains the call bindings. However, for this to occur, Routing Tables and Cause Codes must be properly configured on the SBC Edge.
In order for the fail-over scenario to function properly alternate call routes must be defined.
The subsequent call route entry must specify the Destination Type as Registrar Table.