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Figure 5.2 illustrates the fundamental identity assigned to some of the network elements of an LTE/EPS PLMN.

Figure 5.2 Illustration: identities for LTE network elements.

Several network identities also contain the PLMN Id. The purposes of the network identities shown in Figure 5.2 are described below:

 E‐UTRAN Cell Identity (ECI) (28 bits in length): It is a unique cell identity and cannot be repeated in a PLMN. It is defined as the SIBType1. CellIdentity; refer to TS 36.331 [94]. An ECI together with the PLMN Id constitutes an E‐UTRAN Cell Global Identity (ECGI).

 eNB Id (28 bits length): It identifies an eNodeB within a PLMN.

 Radio Network Temporary Identifier (RNTI) (16 bits length): It identifies a UE having a Radio Resource Control (RRC) connection and also can be scheduled for data transmission/reception.

 MMEC (8 bits length): MME Code – identifies MME with the MME group.

 MMEGI (16 bits length): MME Group Id – identifies the MME Group Id of that an MME belongs to.

 Globally Unique Temporary Identity (GUTI)

In the case of the LTE/EPS system, a mobile device UE is uniquely identified by a GUTI that is allocated by the MME. A GUTI is similar to a P‐TMSI and is used as the identity of a UE during the LTE/EPS mobility management‐related procedures executed between a UE and the MME. A GUTI can be a native or mapped as described later in Section 5.5. A GUTI is constructed from several fundamental network identities as illustrated in Example 5.2.