Passive testing techniques are used when there is no access to the system interface or when the system cannot be interrupted from its normal operation. It is a way of verifying whether the system meets the requirements. Many passive testing techniques consider only the control portion of the protocol neglecting the data portions, or are confronted with an overloaded amount of data values to consider. We propose a novel approach based on protocol properties defined in terms of Input-Output Symbolic Transition Systems (IOSTS) and show how they can be tested on execution traces. In our approach, we check both the control and data portions by integrating the concepts of symbolic execution techniques to provide a property that can be analysed through a parametric trace slicing approach. Our approach is illustrated by the application to the SIP protocol.