1. A policy and charging control method carried out by a server having a policy and charging enforcement function (PCEF), the method comprising the steps of: obtaining identification information for enabling the PCEF to identify from a plurality of service instances, a particular service instance of a particular service type; receiving a packet by the PCEF; determining by the PCEF, whether the packet belongs to the particular service instance by using the identification information and by inspection of at least one of: Open Systems Interconnection (OSI) layer n control information of the packet, wherein n is an integer equal to or larger than 3; and the packet's payload encapsulated by OSI layer 7 control information; upon determining that the packet belongs to the particular service instance, updating a usage parameter representing or identifying an accumulated usage associated with the particular service instance; and making available, to a policy and charging rules function (PCRF), the usage parameter or information derived from the usage parameter.