[cisco-voip] CME Sip Trunk problem

[cisco.voip]

All, please help,
I have a CME--SIP---CCM setup,  The ISR2 CME router is 2900, v8.6 and 
CCM is v7.1.5.
Problem I have is that the CME Branch is a wan connection that dropped 
in and out frequently.
So what happens is the phones hang with the wan connection is down, I 
need a way to force the calls to end on
the CME phones once the SIP Trunk is down.  So when it comes back up, it 
is in a stable state.
When I look at the phones help, I still see sender packets increasing,
but receiver packets have stopped, yet the call to the user shows no 
indication of failure?