Section: 6.2 Identification by a permanent identity
Content: The mechanism described in here allows the identification of a user on the radio path by means of the permanent subscriber identity (IMSI). The mechanism should be invoked by the serving network whenever the user cannot be identified by means of a temporary identity. In particular, it should be used when the user registers for the first time in a serving network, or when the serving network cannot retrieve the IMSI from the TMSI by which the user identifies itself on the radio path. The mechanism is illustrated in Figure 4. Figure 4: Identification by the permanent identity The mechanism is initiated by the visited VLR/SGSN that requests the user to send its permanent identity. The user's response contains the IMSI in cleartext. This represents a breach in the provision of user identity confidentiality.