XID parameters

Hi All As per the specs after PDP context accept mobile station should exchange XID parameters with SGSN. before it initiate transfer of data. As per the literature mobile station if not happy with the negotiated quality of service it will send the deactivation request and I am getting the same. Is this is the only reason mobile station will send deactivation request or something else, which I am missing. Any suggestion to fix this problem. can anybody comment on this please. regards Josh