When i installed the 7920 with CCM3.3(4) using APs 1120 ,i noticed that we have to disable the power save option in the phone settings the phone operates normally ,but when it is enabled the phone starts to lose its connection with the call managers .
Any advises to disable this power save option for ever ( as it returns enabled after power off/ on the device )
Can not disable power save permanently. Also the phone would not be very useful that way as it would only last 3.5 hours. You should ensure you are running the latest code (1.09), which can be downloaded from http://www.cisco.com/cgi-bin/tablebuild.pl/ip-7900ser-crypto.
I do that actually , but what appears is that the ip phone loses its Wifi connectivity with the access point and therefore lose its connectivity with the call managers .
all of this happen when the power save mode is ON !!!
Well if you lose connectivity to the AP, then you lose network connectivity, therefore you will lose connection to the CM. You should reference the design guide @ http://www.cisco.com/en/US/products/hw/phones/ps379/products_implementation_design_guide_book09186a00802a029a.htmlfor more info and/or open a case w/ TAC.
You have holdoff time set for 10 minutes (dot11 holdoff-time 600). This is a global radio paramater. This is disabled by default, but if you want to use this we recommend setting it to less than or equal to a minute for VoWLAN deployments.
The 7920 keepalive timeout is 90 seconds, but could potentially get deregistered still if there is other SCCP traffic bound for the 7920.
We also recommend to optimize for 11mbps (i.e. basic-11.0) unless you have legacy wi-fi clients that require the lower rates or range is required over throughput / capacity. We also recommend this as the cells will be tighter where it will be easier to manage (lower noise levels, reduced same channel overlap). If you do change this to allow only the higher rate, this could potentially effect the current coverage.
Should also enable ARP-caching (dot11 arp-cache) and QBSS (dot11 phone) for VoWLAN deployments.
Also 1.09 is the recommended firmware version at this time.