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A mobile communications system and network comprise numerous physical network elements or resources as well as logical objects or resources that are used as part of the design, development, implementation, and field deployment. Network elements or resource identities are logical in nature. An identity may represent a logical connection and association between two network elements. A network element, say eNodeB, may assign an identity to another network, say UE, to uniquely identify it over a particular logical interface. The network element's identities are divided into the following categories:

 UE/Mobile Station (MS) Identities

 Radio Access Network (RAN), UMTS Terrestrial Radio Access Network (UTRAN), Evolved‐UMTS Terrestrial Radio Access Network (E‐UTRAN), 5G Next‐Generation Radio Access Network (NG‐RAN) Identities

 CN Identities

Figure 5.1 illustrates the above network identities along with their natures.

Figure 5.1 Network identities, their persistency, and presence.

A network element, or a subscriber, or a logical link between peer protocols or other logical resources are identified and addressed with their corresponding identities, which can be a permanent, temporary, static, or dynamic in nature, as shown in Figure 5.1. For example, the core network may allocate a temporary identity to a mobile device for paging purposes. The CN and the access network allocate a temporary identity to an MS/UE as a result of events such as the power off/on or changes in the current location of the mobile device. This is required to protect the real identity of a mobile device while communicating with the network over the air interface.

A permanent identity is assigned to a network element as part of its administrative provision, network planning, and configuration process. For example, an International Mobile Subscriber Identity (IMSI) is allocated to uniquely identify each mobile subscriber in the GSM, UMTS, LTE/EPS, and 5G systems and may be also used to page an MS/UE by the CN.

A network identity can be a local one, i.e. visible to a particular network element such as GSM Visitor Location Register (VLR), GPRS Serving GPRS Support Node (SGSN), and LTE/EPS Mobility Management Entity (MME), or it can be used/visible across the end‐to‐end network element, i.e. from the mobile device to base station controller (BSC), UTRAN, E‐UTRAN, and 5G NG‐RAN to Core Network.

A network identity can be a global one that is exchanged across an interface connecting two peer network elements. For example, in the LTE/EPC system, a UE and MME S1AP identity is exchanged between the eNodeB and the MME over the S1 interface to uniquely identify a UE. Note that the network identities have different lengths.