This Technical Specification defines network functions which are necessary to support services and facilities provided by PLMNs. A summary of the network functions is given in Table 1@ where also an indication is given whether the network must support the function. The table also indicates whether or not a function requires internetworking signalling between PLMNs (i.e. use of Mobile Application Part@ Technical Specification GSM 09.02). All functions require signalling on the radio path as specified in Technical Specification GSM 04.08.