In the proxy registration model, the phones are configured with the Lotus Sametime Unified Telephony as their Primary SIP Server/SIP Registrar. However, the communication layer is set up with DNS SRV records to send all outbound messages to a SIP proxy. With the use of the DNS SRV record, the communication layer would send all outbound messages directly to the Lotus Sametime Unified Telephony in case the SIP proxy is not responding. For a survivable branch office, the SIP proxy must offer the survivability, meaning that it must offer limited SIP Server capabilities when it detects that the Lotus Sametime Unified Telephony is unreachable.
If the phones are not allowed to bypass the proxy in case of proxy failure, the proxy should be deployed in a high availability configuration.
The proxy registration model is a far cleaner survivability solution than the dual registration model because all phones in the branch office will be treated the same in an outage condition (display "Temporary Limited Mode" and act as non-keyset phones) and have virtually no noticeable service interruption in this case. In detail, the proxy registration model has the following advantages when compared to the dual registration model:
The phone is notified of the survivability mode condition and it displays "Temporary Limited Mode". All phones in the branch office remain registered with the proxy. There is no service interruption.
The proxy detects normal mode within 1 minute of the restoration of the WAN or Lotus Sametime Unified Telephony. All phones in the branch office are notified of the normal mode condition.
As a disadvantage an outage of the proxy will lead to a service interruption until the proxy is considered down and is bypassed.
Examples of Survivable SIP Proxies are: Comdasys Convergence, RG2700, RG8700 v1.3.
Parent topic: Survivability Overview