I've just installed a number of 7921 IP Phones at a customer with multiple sites. Each site has a Cisco Call Manager Express running IOS 12.4.15T (Supports 7921) on 2811 and 2801 routers.
The problem I am experiencing is that once the 7921's are online, the first call they make to any IP phone works correctly. From there on, for 70% of the calls made between IP Phones, I can't hear anything from the 7921's earpiece as there is no sounding coming from it!
If the 7921 makes an external call e.g I might call home or my mobile phone, everything works fine and you can hear the other side without a problem. The problem seems to be present only when talking with another IP Phone (any type of ip phone) on the network.
I've checked the firmware on the 7921's and they are the latest (1.0.4), and upgraded the Call Manager Express IOS to at least 12.4.15T which supports the phones (according to Cisco).
The access points used at headquaters are 1100 series and the remote sites have 876W routers which also act as access points for the 7921's.
All sites have WEP enabled (128bit) and MAC address access lists with SSID broadcast blocked.
Any suggestions or ideas are welcome and much appreciated.
what is the usage of wireless during the "trouble call"? Are both sides experiencing the same issue, i.e. no sound, if the call is between two 7921? Are both telephones pingable during the time the issue shows? Is voip traffic arriving at the phone or is it a transport issue?