The same problem as your other threads. For some reason you're trying to make compatibility work between a phone and PBX that weren't built for each other and just happen to both talk SIP.
There's nothing wrong with open vanilla basic SIP. You can do a lot with it. You just have to be ready to debug protocol at a very low level to build the solution you want. Why don't you just buy Alcatel phones for your Alcatel PBX and avoid having to debug problems to this level? Most of the time everybody recommends the simplest solution - even if it costs money, it's better than costing your time later debugging this stuff. I can't speak for everyone on these forums, but we generally don't spend our valuable time trying to make incompatible things work just for the sake of it. You could pay me for a week and I might not be able to make those Avaya phones work. Maybe your Alcatel rep's quote to replace those phones is less than a week of my time! For reasons like that, we generally don't get to such a low level of debugging specifically to address 3rd party interop.
Just buy the right tool for the job.