PROTOCOL SIGNALING PROCEDURES IN LTE

PROTOCOL SIGNALING PROCEDURES IN LTE

Overview:  the ever increasing growth of the internet and services has the need of more and more bandwidth. LTE promises higher data rates. 100 mbps in the downlink and 50 mbps in the uplink in LTE’s first phase it support scalable bandwidth from 1.25 mhz to 20 mhz.

Network architecture:

The architecture of LTE network is given with the various interfaces between the network elements. The functions of various elements are:

eNode:  radio resource management functions , IP header compression, encryption of user data streams, selection of an MME and transmission of paging message.

MME: it provides handovers , authentication and bearer management.

S-GW: the local anchor point of inter-eNode handover, accounting on user.

P-GW: UE IP address allocation , packet filtering , gating and rate enforcement.

BEARERS in LTE:

In LTE, end to end bearers are realized by the EPS bearers which are a collection of radio, S1 and S5/S8 bearers. An EPS bearer identify uniquely an EPS bearer for one UE accessing via E-UTRAN .

There are three kinds of bearer in LTE: radio bearers, S1 bearers and EPS bearers. In the UE, the uplink maps a traffic flow aggregate to an EPS bearer in the uplink direction and in PGW the downlink TFT maps a traffic flow aggregate to an EPS bearer in the downlink.

Radio bearer: a radio bearer transports the packets of an EPS bearer between the UE and eNode B.

S1 bearer: an S1  bearer transports the packets of an EPS bearer between an eNodeB and a S-GW.

S5/S8 bearer : it transports the packets of an EPS bearer between the S-GW and PDN GW.

SYSTEM INFORMATION BROADCASTING:
 to get service from the network , UE has to select the network a UE has to select the network and camp on a cell. For this to happen , the UE has to synchronize itself with the network at the frame and slot level. The network broadcasts this information to help the UEs in their selection process.

RANDOM ACCESS PROCEDURE—SYSTEM ACCESS

The UE can utilize the services of the network once it is synchronised in both the downlink as well as uplink direction. After the PLMN and cell selection the UE is synchronised with the network in the uplink direction. The random access procedure over PRACH is performed by the UE for this purpose. There are two types of RAPs:

Contention based Random Access Procedure: in this mode multiple UEs may attempt to access the network at the same time, thereby resulting in collisions.

Non- contention based Random access procedure : the network initiates this procedure in case of a handover of a UE from one eNode to another in order to keep handover latency under control. There are no collisions with other UE’s because the eNode controls the procedure