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The eNodeB (Evolved Node B) assigns the UE a C-RNTI (Cell Radio Network Temporary Identifier) to identify the UE during exchange of all information over the air. The C-RNTI is assigned during the setup of the RRC Connection (Idle Mode à Connected Mode transition) between a UE and an eNodeB and is valid only for that RRC Connection. Once the UE leaves the coverage area of an eNodeB the RRC Connection must be moved (Inter-eNodeB Handover) and the "new" eNodeB will assign a "new" C-RNTI to the UE. The C-RNTI is an E-UTRAN (Evolved Universal Terrestrial Radio Access Network) specific identifier and the EPC (Evolved Packet Core) Network has no visibility to it.

The MME (Mobility Management Entity) assigns the UE a GUTI (Globally Unique Temporary Identifier) to identify the UE during all message exchanges and procedures with the EPC. The GUTI is assigned during the Attach procedure (Deregistered State à Registered State transition) between the UE and the MME and is valid only as long as the UE is attached to the MME that assigned the GUTI. Once the UE leaves the Tracking Area(s) of an MME the "Attachment" has to be moved (Inter-MME handover) and the "new" MME will assign a "new" GUTI to the UE. Embedded within the GUTI are the PLMN ID of the service provider and the MME Identity. Thus, the GUTI uniquely and globally identifies a UE attached to a specific MME in a specific Service Providers LTE Network in a specific Country. The MME may choose to periodically re-assign a "fresh" GUTI to a UE that is attached to it.

The PGW (Packet Data Network Gateway) assigns the UE an IP address to facilitate data connectivity between the UE and any internal or external PDN (Packet Data Network). This could be an IPv4, IPv6 or Dual Stack IP address and the PGW could use a variety of IP address allocation schemes associated with the type of IP Address. The UE may set up PDN Connections with more than one PGW and may be assigned more than one IP address. The first IP address is assigned to the UE during the Initial Attach procedure and it stays with the UE as long as the UE is attached to the LTE Network. Unlike the other temporary identifiers the IP address is more "persistent" or "sticky" and does not change as long as the UE is attached - thus uninterrupted IP connectivity is provided to the UE. For all practical purposes, the UE is assigned an IP address when it powers on and loses its IP connectivity when it powers off. It is important to recognize that the eNodeB, MME and the SGW do not have any use for this UE IP address for connectivity purposes. It is used for IP forwarding decisions by the PGW and all nodes "north" (between the PGW and the PDN) of the PGW.