Someone transfer an outside call to someone else. The parties talk for minutes (varies), all of a sudden the call go to one-way conversation. We can hear them but they (the outside party) can't hear us. This doesn't happen all the time just once in while. Also, get an AUD019 and/or AUD018 or AUD017 system on PBX terminal. 81 upgraded to CS1000M v5.5. Vendor checking to make sure patches up-todate.