UMTS - Radio Access Network
The more general term "Evolved Radio Access Network" (eRAN), can also be used as part of signaling protocols, as the term "access stratum" (AS) can be used. The comparison reveals that E-UTRAN consists of one type of nodes, namely Evolved Node B (eNodeB), and the variety of interconnections is reduced to a minimum. eNodeB is a radio base station and transmits/receives via its antenna in an area (cell), limited by physical factors (signal strength, interference conditions, and conditions of radio wave propagation). It has logical interfaces X2 with neighboring eNodeB and the EPC via S1. Both have a control part (that is, say for signaling) and a user plane part (for payload data).
Point to the EU reference (which includes radio link interface and a mobile network protocol stack bound) is called "LTE-U u" to indicate that it differs from the legacy counterpart EU X2 connectivity neighboring eNodeBs. They may be considered for most of the E-UTRAN and is used in most cases of handovers between radio cells.
As the UE moves, long handover preparation is done via signaling, through X2 between the two data eNodeBs and affected users can be transmitted between them for a short period of time. Only in special cases, it may happen that X2 is not configured for eNodeB between two neighbors. In this case transfers are always supported, but the preparation of transfer and the data transmission is then made via the EPC. Accordingly, higher latency and less "homogeneity" must therefore be provided.
In more detail, the functions performed by the eNodeB are −
Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Control Mobility, dynamic allocation of resources (i.e. scheduling) to UES as uplink and downlink.
Header compression of IP and encryption of user data stream.
Forwarding the data packets of user plane to the EPC (especially, toward the GW node service).
Transport level packet marking in the uplink, for example, DiffServ code point setting, based on the QoS class index (QCI) of the EPS bearer associated.
Planning and delivery of paging messages (on request of MS).
Planning and transmission of broadcast information (origin of the MME or O & M).
Measurement configuration delivering and reporting on the extent of mobility and programming.
