Today, LTE is on the tip of everyone’s tongues. It’s the up and coming, lighting fast data network we’ve been waiting for. When discussing LTE, however, there are many technical terms and many complexities. To help you better understand, an LTE architecture overview of the LTE network is helpful. Let’s break it down.
LTE contains many components that make it different than General Packet Radio Service (GPRS), High Speed Packet Access) HSPA and any other wireless network for that matter. First of all, radio access for LTE is called Evolved UMTS Terrestrial Radio Access Network (E-UTRAN), and is poised to substantially improve end-user through-puts, sector capacity and reduce user plane latency, bringing significantly improved user experience with full mobility.
System Architecture Evolution (SAE) is the core network architecture of 3GPP’s LTE wireless communication standard. SAE is the evolution of the GPRS Core Network. And, unlike HSPA, LTE has a new packet core, known as the Evolved Packet Core (EPC), which functions as the main core of SAE. The main focus for SAE is to enhance packet switched technology in order to cope with rapid growth in Internet Protocol (IP) traffic, which will help provide higher data rates, lower latency and a more optimized network. [1]
The EPC network architecture, specified by 3GPP standards, will support the E-UTRAN through a reduction in the number of network elements, simpler functionality, improved redundancy but most importantly allowing for connections and hand-over to other fixed line and wireless access technologies, giving the service providers the ability to deliver a seamless mobility experience. [2]
The LTE network architecture consists of the following main elements:
Evolved Radio Access Network (RAN)
The evolved RAN for LTE consists of a single node known as the eNodeB (eNB) that interfaces with the UE. The eNB hosts the PHYsical (PHY), Medium Access Control (MAC), Radio Link Control (RLC), and Packet Data Control Protocol (PDCP) layers that include the functionality of user-plane header-compression and encryption. It also offers Radio Resource Control (RRC) functionality corresponding to the control plane. It performs many functions including radio resource management, admission control, scheduling, enforcement of negotiated UL QoS, cell information broadcast, ciphering/deciphering of user and control plane data, and compression/decompression of DL/UL user plane packet headers.
Serving Gateway (SGW)
The SGW routes and forwards user data packets, while also acting as the mobility anchor for the user plane during inter-eNB handovers and as the anchor for mobility between LTE and other 3GPP technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PDN GW). For idle state UEs, the SGW terminates the DL data path
and triggers paging when DL data arrives for the UE. It manages and stores UE contexts, e.g. parameters of the IP bearer service, network internal routing information. It also performs replication of the user traffic in case of lawful interception.
Mobility Management Entity (MME)
The MME is the key control-node for the LTE access-network. It is responsible for idle mode UE tracking and paging procedure including retransmissions. It is involved in the bearer activation/deactivation process and is also responsible for choosing the SGW for a UE at the initial attach and at time of intra-LTE handover involving Core Network (CN)
node relocation. It is responsible for authenticating the user (by interacting with the HSS). The Non-Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to UEs. It checks the authorization of the UE to camp on the service provider’s Public Land Mobile Network (PLMN) and
enforces UE roaming restrictions. The MME is the termination point in the network for ciphering/integrity
protection for NAS signaling and handles the security key management. Lawful interception of signaling is also supported by the MME. The MME also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME from the SGSN. The MME also terminates the S6a interface
towards the home HSS for roaming UEs.
Packet Data Network Gateway (PDN GW)
The PDN GW provides connectivity to the UE to external packet data networks by being the point of exit and entry of traffic for the UE. A UE may have simultaneous connectivity with more than one PDN GW for accessing multiple PDNs. The PDN GW performs policy enforcement, packet filtering for each user, charging support, lawful Interception and packet screening. Another key role of the PDN GW is to act as the anchor for mobility between 3GPP and non-3GPP technologies such as WiMAX and 3GPP2 (CDMA 1X and EvDO). [2]
Yes, this is just a start to understanding how this new and improved network will operate, but hopefully you have better insight with this LTE architecture overview.
