![](bg2.png)
Figure 1: LTE/SAE High-Level Network Architecture.
When the evolution of the radio interface started, it
soon became clear that the system architecture
would also need to be evolved. Therefore, in
addition to LTE, 3GPP is also defining IP-based, flat
network architecture: System Architecture Evolution
(SAE) as presented in Figure 1. The LTE–SAE
architecture and concepts have been designed for
efficient support of mass-market usage of any IP-
based service. The architecture is based on an
evolution of the existing GSM/WCDMA core
network, with simplified operations. In the User
Plane (UP), for instance, there are only two types of
nodes (Base Stations and Gateways); while in
current hierarchical networks there are four types
(Node B, RNC, SGSN, GGSN). The gateway
consists of two logical UP entities, Serving Gateway
(S-GW) and Packet Data Network Gateway (PDN-
GW). Flat architecture with less involved nodes
reduces latencies and improves performance.
Another simplification is the separation of the
Control Plane (CP), with a separate Mobility-
Management Element (MME). A key difference
from current networks is that it is defined to support
packet-switched traffic only.
The only node in the Evolved Universal
Terrestrial Radio Access (eUTRAN) is the eUTRAN
Node-B (eNode-B, eNB in Figure 1). It is a radio
base station that is in control of all radio related
functions in the fixed part of the system. Typically,
the eNode-Bs are distributed throughout the
networks' coverage area, each residing near the
actual radio antennas. The interface between the
eNode-B and the gateways is the S1-U; the interface
between the eNode-B and the MME is the S1-C. The
interface between peers eNode-Bs is the X2. The
backhaul links are implementation of these three
interfaces and any required aggregation.
A noteworthy fact is that most of the typical
protocols implemented in today's Radio Network
Controller (RNC) are moved to the eNode-B. The
eNode-B is also responsible for header compression,
ciphering and reliable delivery of packets. On the
control plane, functions such as admission control
and radio resource management are also
incorporated into the eNodeB. Benefits of the RNC
and Node-B merger include reduced latency with
fewer hops in the media path, and distribution of the
RNC processing load.
The Policy and Charging Resource Function
(PCRF) is the network element that is responsible
for Policy and Charging Control (PCC). It makes
decisions on how to handle the services in terms of
QoS, and provides information to the PDN-GW, and
if applicable also to the S-GW, so that appropriate
bearers and policing can be set up.
The Home Subscription Server (HSS) is the
subscription data repository for all permanent user
data. It also records the location of the user in the
level of visited network control node, such as MME.
The IP Multimedia Sub-system (IMS) is service
machinery that the operator may use to provide
services using the Session Initiation Protocol (SIP).
For additional information on LTE network see
(Holma and Toskala, 2009, Dahlman et al. 2007).
3 BASE STATION APPLICATION
OPTIMIZER
We suggest a simple solution to the backhaul
bottleneck problem. The traffic load on the backhaul
links can be reduced by replacing the traditional
Base Station entity with the BS-OPT, a smart entity
capable of analyzing and optimizing the user data in
the application level. This section describes the
suggested solution architecture, support for user
mobility and finally discusses possible benefits and
limitations.
3.1 Architecture for the Base Station
Application Optimizer
Two options are considered for the new BS-OPT
architecture as described in Figure 2. In the first
architecture the BS-OPT is a stand-alone entity, not
integrated inside the base station, probing and then
analyzing and manipulating the traffic. The second
architecture is an integrated unit inside the base
station. Pros and cons of each solution are discussed
below.
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