Administrator’s Guide for SIP-T23 & T23P & T23G IP Phones334Phone Configuration for Redundancy ImplementationTo assist in explaining the redundancy behavior, an illustrative example of how an IPphone may be configured is shown as below. In the example, server redundancy forfallback and failover purposes is deployed. Two separate SIP servers (a working serverand a fallback server) are configured 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 isresolved to multiple SIP servers for failover purpose. The working server is deployed inredundant pairs, designated as primary and secondary servers. The primary server hasthe highest priority server in a cluster of servers resolved by the DNS server. Thesecondary server backs up a primary server when the primary server fails and offersthe same functionality as the primary server.Fallback Server: Server 2 is configured with the IP address of the fallback server. Forexample, 192.168.1.15. A fallback server offers less functionality than the working server.Phone RegistrationRegistration methods of the fallback mode: Concurrent registration: The IP phone registers to two SIP servers (working serverand fallback server) at the same time. In a failure situation, a fallback server cantake over the basic calling capability, but without some of the advanced featuresoffered by the working server (default registration method). Successive registration: The IP phone only registers to one server at a time. The IPphone first registers to the working server. In a failure situation, the IP phoneregisters to the fallback server.When registering to the working server, the IP phone must always register to the primaryserver first except in failover conditions. When the primary server registration is
