Технологии цифровой сотовой связи и телевещания

1. Технологии цифровой сотовой связи и телевещания Лекция 8 Мобильная сотовая связь 4G. Архитектура сети LTE.

2. Network architecture

3. Introduction

4. 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 PacketCore, EPC), то она обозначается термином ‘SAE’ (System Architecture Evolution). Вместе LTE and SAE включают в себя Evolved Packet System (EPS).

5. 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.

6. 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.

7. 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).

8. 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)

9. Functional split between E-UTRAN and EPC

10. 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.

11. 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.

12. 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.

13. Bearer establishment procedure example

14. Inter-Working with other RATs P-GW – anchor for all non-3GPP technologies (WiMAX); S-GW – anchor for other 3GPP technologies (UMTS, GPRS).

15. Inter-Working with other RATs Voice in LTE: • VoIP (using IMS services); • Circuit-Switched FallBack (CSFB).

16. 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

17. 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.

18. 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

19. S1 Interface Mobility over S1: • Intra-LTE mobility • Inter-LTE mobility • Mobility towards Home eNodeB

20. 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.

21. 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).

22. 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

23. Спасибо