Hi, I am seeing a strange call cut off problem with GXP-1200 phones.  Basically mid call the GXP-1200 sends a bye message cutting the call off.  The user hasn't pressed anything and the farside hasn't hungup.  So far it happens on 4 different gxp-1200 phones.  I have tried replaced them and the ethernet cables but it still happens.  There is no other call signalling prior to the BYE message.   The phones are on firmware 1.1.6.16.  It only happens on outgoing calls.  Session Timers are disabled.  The time of the cut of is variable from a few seconds to several minutes.  The sip server is asterisk 1.2.29.  Anyone got any ideas as to why the phone should disconnect itself?  Do the phones disconnect under certain circumstances? Any help would be appreciated.