In August of 2005, we were at a vendors site and watched it happen. We had two 8500's; one in active mode and the other in standby, or failover, or whatever the term was (My Avaya terminology is coming along slowly). We pulled the patch cable to the primary controller and picked up the phone; NO DIAL TONE. We waited and watched the phone for about 90 seconds. All it did was say "tring to connect to 192.168.X.X. After about 4 minutes, it registers with the secondary controller and we were able to make calls again.
We did the exact same test on Cisco sets, and once we pulled the plug on the primary Call Manager, we picked up the set, it immediatly registers to the secondary Call Manager and gave us dial tone.
As I said, that was almost a year ago, so I reserve the right to be wrong on todays functionality. The expanation provided was as stated above; a link-flap timer. I have asked our current vendor to provide updated information on this, so far with no response.
I did read that configuring the S8500 units as LSP's vs. ESS does help in switchover from the primary server to the backup (BCR March 2006). Our concern was when you do not have a server at the same location as your phones, or you lose a local link, so that connectivity may go down totally, then reroute (i.e. a WAN link with DSL for backup).
Hope this helps explain where I got this, and I would love to hear any updates on this issue. As I continue down this road of VoIP with my current employer, I want to be as informed as possible, and make the right suggestions and proposals for my company.
Thanks,
Scott M.
BTW, do you remember when they announced the results of the tests? I was at VoiceCon this year and last, and I don't remember a workshop they discussed that. This would be good info to have as well.