The E- Node B is the only node for the E-UTRAN. If you have a slightest idea of any of previous telecom technologies like GSM, CDMA and/or WCDMA , you might know that all the other RAN technologies used more than one node in the RAN environment. For example, in case of WCDMA , we had a RNC and an Node-B. The RNC took care of Radio Resource Management and Mobility Management. All these functions have been implemented in the NodeB to make them “efficient” and smart. This has led to an “evolved” version of Node- B called E-Nodeb.
So , you will think, what are the benefits of this evolution? Well, when you reduce the number of entities involved during a call flow, the response time increases. It also simplifies the networks.
Functions of E- Nodeb
E-Nodeb or Evolved Node-b is a smart entity that has the functions of traditional Node-b as well as that of the RNC. The major function of the E-Nodeb are as follows.
Functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of user data stream;
Selection of an MME at UE attachment when no routing to an MME can be determined from the information provided by the UE;
Routing of User Plane data towards Serving Gateway;
Scheduling and transmission of paging messages (originated from the MME);
Scheduling and transmission of broadcast information (originated from the MME or O&M);
Measurement and measurement reporting configuration for mobility and scheduling;
Scheduling and transmission of ETWS messages (originated from the MME).
The above chunk of data is used from the 3GPP TS 36.300. To have a simple understanding of what e-NodeB does, think of all the features that you get when you use a mobile service. You are able to recieve the data (Radio Bearer control takes care of this, it is used to deliver C-plane and U-plane data over Uu interface.), you are able to move from one location to another location without getting disconnected (Connection Mobility Control deals with the management of radio resources in relation to idle and connected mode mobility. The same concept that is used by spider-man). Other than this an E-NodeB also takes care of other functions as well, which might seem abstract to you. The first one is Admission Control (eg- you can not access any other network, than that of your connection plan) and Dynamic allocation of resources, which distributes the available resources like RRB’s depending upon the demand and availability concept.
eNB interfaces with the System Architecture Evolution (SAE) core (also known as Evolved Packet Core (EPC)) and other eNB as follows:
- eNB uses the S1-AP protocol on the S1-MME interface with the Mobility Management Entity (MME) for control plane traffic.
- eNB uses the GTP-U protocol on the S1-U interface with the Serving Gateway (S-GW) for user plane traffic.
Collectively the S1-AP and S1-U interfaces are known as the S1 interface, which represents the interface from eNB to the EPC.
- eNB uses the X2-AP protocol on the X2 interface with other eNB elements.