The following are some frequently asked questions on SIP Phone failover.
Q1. How does Call Manager know that the SIP phone becomes un-reachable?
A: Cisco Unified Communications Manager knows that the phone is unreachable when cucm tries to send some message to phone and it gets tcp connection failure, or cucm does not receive re-REGISTER message.
Q2. How does the sip phone know that CallManager becomes un-reachable and starts to failover?
A: SIP Phone knows that CUCM is unreachable when phone tries to send some message to cucm and get tcp connection failure and start failover process. Q3. Is geometric timers applicable to Cisco SIP IP phones?
A:Yes, geometric timers are applicable to Cisco SIP IP phones.