Abstract: Number portability is a service where a subscriber can keep his old telephone number within a portability cluster and thus retain easy contactibility. Because of number portability, a called address, i.e. B-number, no longer refers to the subscription network/number range owner and the old rule “the number range of the called party reveals the tariff level” is no longer valid. To overcome this defect all intelligent network-like service invocation requests are routed (3-2) via a network node performing a number portability function to the network node controlling the service. The node performing the number portability function performs (3-3) a mapping of the B-number and relays (3-4) the service invocation requests indicating the subscription network/number range owner.

Abstract: 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.