The phone loses TCP connection with the SIP proxy: If the TCP socket closes or the TCP keep-alive timer times out, the phone has lost connection with the SIP proxy. The default value of the TCP keep-alive timer is 45 seconds. To modify the timer, update the TCP_KEEP_ALIVE_TIME parameter in the 46xxsettings.txt file.

Proxy fails to respond to a SIP INVITE message within the specified time: If the phone sends a SIP INVITE message to the proxy and the proxy does not respond within a specified time, the phone has lost connection with the SIP proxy. The default response time is set to 5 seconds. To modify the response time, update the FAST_RESPONSE_TIMEOUT parameter in the 46xxsettings.txt file . The TIMER B parameter in Avaya Aura® System Manager precedes over the 46xxsettings.txt file parameter.

Proxy fails to respond to a SIP registration method: After the initial registration, the phone periodically sends a re-registration message to the proxy. If the proxy fails to respond to the re-registration message, the phone initiates a failover. The parameter REGISTERWAIT in the 46xxsettings.txt file specifies the period of re-registration. The Registration Expiration Time parameter in Avaya Aura® System Manager precedes over the 46xxsettings.txt file parameter.