Configuring Advanced Features151Phone Configuration for Redundancy ImplementationTo assist in explaining the redundancy behavior, an illustrative example of how an IPphone may be configured is shown next. In the example, server redundancy forfallback and fail-over 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, sip:user@example.com. DNS mechanism is used such that the working serveris capable of resolving to multiple physical SIP servers for fail-over purpose. The workingserver is deployed in redundant pairs, designated as primary and secondary servers.The primary server is the highest priority server in a cluster of servers resolved by theDNS server. The secondary server backs up a primary server when the primary serverfails. It offers the same functionality as the primary server.Fallback Server: Server 2 is configured with the address of the fallback server. Forexample, 192.168.1.15. A fallback server offers lesser functionality than the workingserver.Phone RegistrationThe registration methods of the fallback mode include: 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 richer featuresoffered by the working server. 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.VoIPon www.voipon.co.uk sales@voipon.co.uk Tel: +44 (0)1245 808195 Fax: +44 (0)1245 808299
