Технологии цифровой сотовой
связи и телевещания
Лекция 8
Мобильная сотовая связь 4G.
Архитектура сети LTE.
NETWORK ARCHITECTURE
Introduction
Introduction
LTE has been designed to support only Packet-Switched (PS)
services.
Термин ‘LTE’ (Long-Term Evolution) обозначает эволюцию сети
радиодоступа (Evolved-UTRAN, E-UTRAN).
Что касается эволюции ядра сети (Evolved Packet Core, EPC),
то она обозначается термином ‘SAE’ (System Architecture
Evolution).
Вместе LTE and SAE включают в себя Evolved Packet System
(EPS).
Overall Architectural Overview
Network is comprised of:
• the access network (i.e. E-UTRAN) = set of evolved
NodeB (eNodeB), which connects to the UEs;
• the CN (i.e. EPC) = all other logical nodes.
The Core Network (EPC)
EPC:
• PCRF (Policy Control and Charging Rules Function) is responsible for policy
control decision-making. PCRF provides QoS authorization that decides how a
certain data flow will be threated in the P-GW and ensures that this is in
accordance with the user’s subscription profile.
• P-GW (PDN Gateway) is responsible for IP address allocation for the UE, as
well as QoS enforcement and flow-based charging according to rules from
PCRF (filtering of downlink user IP packets into the different QoS-based
bearers). P-GW is also the mobility anchor for inter-working with non-3GPP
technologies;
• S-GW (Serving Gateway). All user IP packets are transferred through the S-GW.
S-GW retains the information about the bearers when UE is in idle state;
buffers downlink data while MME initiates paging; is local mobility anchor for
data bearers when the UE moves between eNodeBs. S-GW is mobility anchor
for inter-working with other 3GPP technologies. In visited network S-GW
collect information for charging.
The Core Network (EPC)
EPC:
• MME(Mobility Management Entity) is the control node which processes the
signaling between the UE and the CN (Non-Access stratum (NAS) protocols).
Functions: bearer management (establishment, maintenance and release),
connection management (establishment of connection and security between
CN and UE) and others.
• HSS (Home Subscriber Server) contains user’s subscription data and holds the
identity of the MME to which UE is currently attached. The HSS may also
integrate the AuC.
• E-SMLC (Evolved Serving Mobile Location Centre) manages the overall
coordination and scheduling of resources required to find the location of a UE.
• GMLC (Gateway Mobile Location Centre) contains functionalities required to
support LoCation Services (LCS).
The Access Network (E-UTRAN)
E-UTRAN functions:
•
•
•
•
Radio Resource management;
Header Compression;
Security;
Positioning (provides necessary
measurements to the E-SMLC);
• Connectivity to the EPC (signaling
towards the MME and bearer path
towards the S-GW)
Functional split between E-UTRAN and EPC
Roaming Architecture
A network run by one operator in one country is known as a PLMN (Public Land Mobile
Network). HPLMN – Home PLMN. VPLMN – Visited PLMN.
QoS and EPS Bearers
A bearer is an IP packet flow with a defined Quality of Service (QoS).
Two bearers categories:
•
•
Minimum Guaranteed Bit Rate (GBR) bearers – for applications such as VoIP;
Non-GBR bearers – for applications such as web browsing and FTP transfer.
QoS and EPS Bearers
Packet filtering into different bearers is based on Traffic Flow Templates (TFTs), which
use IP header information (source and destination IP addresses, port numbers, …).
UpLink TFT (UL TFT) – in the UE.
DownLink TFT (DL TFT) – in the P-GW.
Bearer establishment procedure example
Inter-Working with other RATs
P-GW – anchor for all non-3GPP technologies (WiMAX);
S-GW – anchor for other 3GPP technologies (UMTS, GPRS).
Inter-Working with other RATs
Voice in LTE:
• VoIP (using IMS services);
• Circuit-Switched FallBack (CSFB).
S1 Interface
Initiation over S1:

The initialization of the S1-MME starts with the identification of the MME
to which the eNodeB must connect.

Establishment of the SCTP association between eNodeB and MME.

‘S1 SETUP’ procedure initiated by the eNodeB
S1 Interface
Context Management over S1:

UE is associated to one particular MME for all its communications.

This MME create a context for the UE.

When the UE becomes active, the MME provides this context
information to eNodeB
Bearer Management over S1

For each bearer requested to be set up, the eNodeB provided all
necessary information.
S1 Interface
Paging over S1:
•
•
In order to re-establish a connection towards a UE in idle mode, the MME distributes a
‘Paging Request’ message to the relevant eNodeBs
When receiving this request, the eNodeB sends a page over the radio interface.
Load Management over S1
Trace Function
Delivery of Warning Messages
S1 Interface
Mobility over S1:
•
•
•
Intra-LTE mobility
Inter-LTE mobility
Mobility towards Home eNodeB
X2 Interface
The X2 interface may be established between eNodeBs.
Two types of information may need to be exchanged
over X2 to drive the establishment of an X2 interface:
• Load or interference related information
• Handover related information.
X2 Interface
Mobility over X2
Handover via the X2 interface is
triggered by default (unless
there is no X2 interface
established or the source
eNodeB is configured to use the
S1-handover).
X2 Interface
Load and Interference Management over X2
The exchange of load information between eNodeBs is of key importance in the flat
architecture used in LTE, as there is no central RRM node (as RNC in UMTS).
Two purposes:
 Load balancing
 Interference coordination
СПАСИБО