Configuring Advanced Features571depends on the SIP protocol being used as described below: If TCP is used, then the signaling fails if the connection or the send fails. If UDP is used, then the signaling fails if ICMP is detected or if the signal times out. If thesignaling has been attempted through all servers in the list (this list contains all the serveraddresses resolved by the DNS server) and this is the last server, then the signaling failsafter the complete UDP timeout defined in RFC 3261. If it is not the last server in the list,the maximum number of retries depends on the configured retry counts (configured bythe parameter “account.X.sip_server.Y.retry_counts”).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. As soon as the primary server registration succeeds, it returns to being theworking server.Registration methods of the fallback mode include (not applicable to outbound proxy servers): Concurrent registration (default): The IP phone registers to SIP server 1 and SIP server 2(working server and fallback server) at the same time. Note that although the IP phoneregisters to two SIP servers, only one server works at the same time. In a failure situation, afallback server can take over the basic calling capability, but without some advancedfeatures (for example, shared lines and MWI) offered by the working server. Successive registration: The IP phone only registers to one server at a time. The IP phonefirst registers to the working server. In a failure situation, the IP phone registers to thefallback server, and the fallback server can take over all calling capabilities.For more information on server redundancy, refer toServer Redundancy on Yealink IP Phones.ProcedureServer redundancy can be configured using the following methods.CentralProvisioning(ConfigurationFile).cfgConfigure the SIP server redundancy.Parameters:account.X.sip_server.Y.addressaccount.X.sip_server.Y.portaccount.X.sip_server.Y.expiresaccount.X.sip_server.Y.retry_counts
