The present invention discloses a general protocol for a service control point (SCP) in a network system. The network system comprises at least one first type network element (SCP) and at least one second type network element (SSP) for transmitting messages to the first type network elements (SCP), respectively using a specific protocol. The first type network elements (SCP) are able to process the received protocol-specific messages and to transmit messages to said second type network elements by using service logic programs (SLP). In addition, the system comprises a definition means (1) for defining protocol definitions related to one message into a general protocol definition for the message, and for providing general protocol definitions for all possible transmitted messages for each of the first type network elements (SCP). Each of the first type network elements (SCP) in the system comprises a conversion means (2) for converting the provided general protocol definitions into one general message set that is used in the respective first type network element (SCP), and a selection means (3) for selecting converted protocol definitions in the converted general protocol definition for a received protocol-specific message and for a message to be transmitted by the respective first type network element out of the general message set, and for providing the selected converted protocol definitions for the received message to the service logic programs (SLP) for processing the received message, and for transmitting the selected converted protocol definitions for the message to be transmitted.