The EPS Bearer is thus managed by the MME, which signals to the UE when it needs to activate, modify, or deactivate a particular EPS Bearer. The Radio Bearer is managed by the base station (which might further be controlled by the MME). Thus there are always two connections between the UE and the communication network: one for the user data transmitted using the established EPS bearer (also known as the user plane) and another one for managing the EPS Bearer and its elements (also known as the control plane). Further details of the EPS Bearer architecture can be found in 3GPP TS 23.401 V11.2.0 and 3GPP TS 36.300 V11.2.0, the contents of which are hereby incorporated by reference.

As part of the Long Term Evolution (LTE) Of UTRAN (UMTS Terrestrial Radio Access Network) referred to as E-UTRAN, there are plans to introduce a feature of direct device-to-device (D2D) communication when the UE can communicate user data to another UE that is within the transmission range of the first UE without the need to use LTE network resources. This direct communication would result in better utilization of the available resources, especially on the radio interface, where these are limited.

D2D services might be particularly beneficial for users of professional mobile radio (PMR) networks, such as Terrestrial Trunked Radio (TETRA), and the like. Since PMR networks are mainly used by government agencies, emergency services, (police forces, fire departments, ambulance), rail transportation staff, transport services and the military, D2D voice and/or data services may be used:

• • to ensure increased resilience in case of network failure by using direct mode as a fall-back solution;