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Design, Deployment and Performance of 4G-LTE Networks: A Practical Approach by Mahmoud Sherif, Mohamed El-saidny, Ayman ElNashar

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Chapter 2LTE Air Interface and Procedures

Mohamed A. El-saidny

2.1 LTE Protocol Stack

The LTE (long term evolution) air interface provides connectivity between the user equipment (UE) and the eNB (eNodeB). It is split into a control plane and a user plane, as described in Chapter 1. Among the two control plane signalings, the first is provided by the access stratum (AS) and carries signaling between the UE and the eNB. The second carries non-access stratum (NAS) signaling messages between the UE and the MME (mobility management entity), which is piggybacked into an RRC (radio resource control) message. The user plane delivers the IP (Internet protocol) packets to and from the EPC (evolved packet core), the S-GW (serving gateway), and the PDN-GW (packet data network gateway).

The structure of the lower layer protocols for the control and user planes in AS are the same. Both planes utilize the protocols of PDCP (packet data convergence protocol), RLC (radio link control), and MAC (medium access control), as well as the PHY (physical layer) for the transmission of the signaling and data packets (1).

NAS is the layer above the AS layers. There are also two planes in NAS; the higher layer signaling related to the control plane and the IP data packets of the user plane. NAS signaling exists in two protocol layers, EMM (EPS mobility management) and ESM (EPS session management), as discussed in Chapter 1. The NAS user plane is IP-based. The IP data packets pass directly into the PDCP ...

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