A method for tracing a session or call in a network environment, comprising the step of transmitting a trace invocation from a control plane network element to another control pane network element or a user plane network element. According to a first aspect, a trace report is generated in the S-CSCF of the called party. This overcomes the lack of being able to provide detailed information about the interworking between the User Equipment (UE) and the IMS, in setting up IP multimedia sessions. According to a second aspect trace reports are generated in all the network functions involved in session setup.