Configuring Advanced Features649Phone Configuration for Redundancy ImplementationTo assist in explaining the redundancy behavior, an illustrative example of how an IP phone maybe configured is shown as below. In the example, server redundancy for fallback and failoverpurposes is deployed. Two separate servers (a working server and a fallback server) areconfigured for per line registration.Working Server: Server 1 is configured with the domain name of the working server. Forexample: yealink.pbx.com. DNS mechanism is used such that the working server is resolved tomultiple servers for failover purpose. The working server is deployed in redundant pairs,designated as primary and secondary servers. The primary server has the highest priority serverin a cluster of servers resolved by the DNS server. The secondary server backs up a primaryserver when the primary server fails and offers the same functionality as the primary server.Fallback Server: Server 2 is configured with the IP address of the fallback server. For example,192.168.1.15. A fallback server offers less functionality than the working server.Phone RegistrationRegistration method of the failover mode:The IP phone must always register to the primary server first except in failover conditions. If thisis unsuccessful, the phone will re-register as many times as configured until the registration issuccessful. When the primary server registration is unavailable, the secondary server will serve asthe working server.Registration methods of the fallback mode include: Concurrent registration (default): The IP phone registers to two SIP servers (workingserver and fallback server) at the same time. In a failure situation, a fallback server can takeover the basic calling capability, but without some advanced features (for example, sharedlines, call recording and MWI) offered by the working server. It is not applicable tooutbound proxy servers
