I-RAT Network Architecture

I-RAT Network Architecture

S3 & S4 Interfaces:

Ø  S3/S4 are Interfaces between EPC and 2G/3G packet switched core network domain.

Ø  They would allow inter-system changes between SAE and 2G/3G

Ø  The S3 is a pure signaling interface used to coordinate the inter-system change between MME  and SGSN

Ø  The S4 is the user plane interface and it is located between SGSN and serving SAE GW.

Ø  This would allow to either forward packet data from EUTRAN via serving SAE GW to SGSN (and then to GGSN) or from 2G/3G RAN to SGSN to serving SAE GW to PDN GW.

UTRAN Direct Tunnel:

Ø  S12 is the interface between EPC and 3G Radio access network

Ø  It would allow inter-system changes between SAE and 3G

Ø  The S12 is the user plane interface used for tunneling user data directly between the Serving SAE SW and the UTRAN

Ø  This would allow to forward packet data from 3G RAN to serving  SAE GW to PDN GW.

Ø  It is based on the Gn interface between the SGSN and the GGSN and so uses the GTP-U protocol.

LTE Network Interfaces

Network Interfaces:

Evolved Packet System (EPS) contains following network elements:

Ø  LTE-Uu: Allows data transfer between the eNodeB and the UE’s. All the functions and protocols needed for this transfer and the control operations of the E-UTRAN Uu interface are implemented in the eNodeB.

Ø  S1-C or S1-MME: Reference point for the control plane protocol between E-UTRAN and MME.

Ø  S1-U: Reference point between E-UTRAN and Serving GW for the per bearer user plane tunneling and inter eNodeB path switching during handover.

Ø  S5: It provides user plane tunneling and tunnel management between Serving GW and PDN GW. It is used for Serving GW relocation due to UE mobility and if the Serving GW needs to connect to a non-collocated PDN GW for the required PDN connectivity.

Ø  S6a: It enables transfer of subscription and authentication data for authenticating/authorizing user access to the evolved system (AAA interface) between MME and HSS.

Ø  Gx: It provides transfer of (QoS) policy and charging rules from PCRF to Policy and Charging Enforcement Function (PCEF) in the PDN GW. The interface is based on the Gx interface.

Ø  Gxa: It provides transfer of (QoS) policy information from PCRF to the Trusted Non-3GPP accesses.

Ø  Gxc: It provides transfer of (QoS) policy information from PCRF to the Serving Gateway

Ø  S9: It provides transfer of (QoS) policy and charging control information between the Home PCRF and the Visited PCRF in order to support local breakout function.

Ø  S10: Reference point between MMEs for MME relocation and MME to MME information transfer.

Ø  S11: Reference point between MME and Serving GW

Ø  SGi: It is the reference point between the PDN GW and the packet data network. Packet data network may be an operator external public or private packet data network or an intra-operator packet data network, e.g. for provision of IMS services. This reference point corresponds to Gi for 3GPP accesses.

Ø  X2: The X2 reference point resides between the source and target eNodeB.

LTE-Uu Interface or Radio Interface:

Ø  Air Interface of E-UTRAN.

Ø  Based on OFDMA in downlink and SC-FDMA in uplink

Ø  Supports FDD and TDD mode

Ø  Supports all 3GPP defined frequency bands

Ø  Scalable bandwidth 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz and 20MHz.

Ø  Theoretically peak data rate is 173 Mbps in downlink and 53 Mbps in uplink

Ø  MIMO is a major component but optional.

Ø  No user dedicated channel.

Radio Interface:

Ø  The physical layer provides the basic bit transmission functionality over air.

Ø  MAC main functions:

ü  Mapping of logical channels onto transport channels

ü  Error correction through HARQ (Hybrid Automatic Repeat Request).

Ø  RLC main Functions:

ü  Concatenation, segmentation and reassembly of higher layer data.

ü  Error correction through ARQ (Automatic Repeat Request)

Ø  PDCP main Functions:

ü  Header error compression and de-compression

ü  Ciphering and deciphering

Ø  RRC main functions:

ü  Broadcast of system information

ü  RRC connection control

ü  I-RAT mobility

ü  Measurement configuration and reporting

ü  Other functions (eg. Transfer NAS messages)

ü  Generic protocol error handling

ü  Support of self-configuration and self-optimization.

X2 Interface:

Ø  Inter eNB interface.

Ø  Intra LTE Access system mobility support for UE

ü  Context transfer

ü  Control of user plane tunnels

ü  Handover cancellations

Ø  Load Management (used for interference management)

Ø  X2 management and error indication

Ø  The X2-U interface provides non-guaranteed delivery of user plane PDUs between eNBs.

S1 Interface:

Ø  S1 Paging function

Ø  UE context Management function.

Ø  Mobility function for UEs

ü  Intra LTE handover

ü  Inter 3GPP RAT handover

Ø  eRAB Service Management function

Ø  NAS signaling transport function

Ø  S1 interface management functions (eg error indication and reset)

Ø  RAN information management function

Ø  Configuration transfer function (eg SON (Self Optimizing Network) information)

Ø  The S1-U interface provides non-guaranteed delivery of user plane PDUs between the eNB and the SGW

S11 Interface:

Ø  Interface between MME and a SGW

Ø  Control plane only interface

Ø  A single MME can handle multiple SGW each one with its own S11 interface

Ø  Used to coordinate the establishment of SAE bearers within EPC

Ø  SAE bearer setup can be started by the MME (default SAE bearer) or by SGW (dedicated SAE bearer).

S5/S8 Interface:

Ø  Interface between SGW and PGW

Ø  S5: If SGW and PGW belong to the same PLMN (non-roaming case)

Ø  S8: If SGW and PGW belong to different PLMN (roaming case)

Ø  S8 = S5 + inter-operator security functions

Ø  Mainly used to transfer user packet data between PGW and SGW.

Ø  Signaling on S5/S8 is used to setup the associated bearers resources

Ø  S5/S8 can be implemented either on 3GPP solution (GTP) or IETF solution (MIPv6).

S6a Interface:

Ø  Interface between the MME and the HSS

Ø  The MME uses it to retrieve subscription information from HSS (handover/tracking area restrictions, external PDN allowed, QoS, etc) during attaches and updates.

Ø  The HSS can during these procedures also store the user’s current MME address in its database.

Gx, SGi and Rx+ Interfaces:

Gx:

Ø  Interface between PDN GW and PCRF

Ø  It Allows:

ü  The PCRF to request the setup of a SAE bearer with appropriate QoS

ü  The PDN GW to ask the QoS of an SAE bearer to setup.

ü  To indicate EPC status changes to the PCRF to apply a new policy rule

SGi:

Ø  Interface used by the PDN GW to send and receive data to and from the external data network.

Ø  It is typically either IPv4 or IPv6 based

Ø  Downlink data coming from the external PDN must be assigned to the right SAE bearer of the right user by analysis of the incoming packet’s IP addresses, port numbers,etc.

Ø  The interface corresponds to the Gi interface in 2G/3G networks

Rx+:

Ø  Interface between PCRF and the external PDN network/operator IMS

S9 Interface:

Ø  Interfaces between the hPCRF and the vPCRF used in roaming cases

Ø  It is used enforcement in the vPLMN of the dynamic control policies from the hPLMN.

LTE Network Architecture

LTE Network Architecture:

Ø  UE: User Equipment

Ø  E-UTRAN: Evolved UMTS Terrestrial Radio Access Network.

Ø  eNobeB (eNB): Evolved NodeB

Ø  MME: Mobile Management Entity

Ø  EPC: Evolved Packet Core

Ø  SGW: Serving Gate Way

Ø  PGW: Packet Gate way

Ø  HSS: Home Subscriber Server

Ø  PCRF: Policy & Charging Rule Function

E-UTRAN (Evolved UMTS Terrestrial Radio Access Network)

ü  It supports the LTE air Interface.

ü  EUTRAN consists of eNB’s.

ü  It provides user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE.

ü  The eNB’s are interconnected to each other via X2 interface.

ü  The eNB’s are connected to MME via S1-MME interface.

ü  The eNB’s are connected to SGW via S1-U Interface.

ü  The eNB’s support Many to many relation with MME/SGW.

eNodeB Functions:

ü  Radio Resource Management:

•Radio Bearer Control (i.e. the establishment, maintenance and release of Radio Bearers).

•Radio Admission Control, to admit or reject the establishment requests for new radio bearers.

•Connection Mobility Control, concerned with the management of radio resources in connection with idle or connected mode mobility.

•Dynamic resource allocation for UEs in both uplink and downlink (also called packet scheduling).

ü  IP header compression and encryption of user data stream.

ü  Selection of an MME at Initial UE attach when no routing to an MME can be determined from the information provided by the UE

ü  Routing of User Plane data towards Serving Gateway.

ü  Scheduling and transmission of paging messages (originated from the MME).

ü  Scheduling and transmission of broadcast information (originated from the MME or O&M).

ü  Measurement and measurement reporting configuration for mobility and scheduling.

    

                                 

 MME (Mobility Management Entity):

ü  It is a pure signaling entity inside the EPC.

ü  MME is connected to eNB via S1-MME interface.

ü  MME controls one or several SGWs via S11 interface

ü  MME is connected to HSS via S6a interface.

ü  MME can be connected to SGSN’s via S3 interface.

ü  MME are interconnected via S10 interface.

ü  Manages mobility, UE Identities and security parameters.

MME Functions:

ü  Non Access Stratum (NAS) signaling and security
   The NAS protocol is used on the control plane between the UE and the core network, the MME (Mobility Management Entity). The NAS layer is handling mobility related functions between the   UE and the core network, like attach and tracking area update, authentication and security. It is also responsible for establishing and maintaining IP connectivity between the UE and the core network.

ü  Inter CN node signaling and SGSN selection for mobility between 3GPP access networks.

ü  Idle mode UE reachability (including control and execution of paging retransmission)

ü  Tracking Area list management (for UE in idle and active mode)

ü  PDN GW and Serving GW selection

ü  MME selection for handovers with MME change

ü  Roaming (terminating S6a towards home HSS)

ü  User authentication and authorization support

ü  Bearer management functions including dedicated bearer establishment

ü  Lawful Interception of signaling traffic.

                                  

SGW (Serving Gateway):  The Serving Gateway is the node that terminates the interface towards EUTRAN. For each UE associated with the EPS, at a given point of time, there is one single Serving Gateway.

ü  It manages the user data path (EPS Bearers) within EPC.

ü  It transmits and receives packet data to and from eNB via S1-U interface.

ü  SGW is controlled by one or more MMEs via S11 interface

ü  For interworking to other 3GPP RATs, it can be connected to SGSN  via S4 interface or to the RNC via S12 interface (when Direct Tunnel feature is implemented).

ü  It relays the packet data to or from the PDN gateway via S5/S8 interface.

SGW Functions:

ü  Packet Routing and Forwarding.

ü  The local Mobility Anchor point for inter-eNB handover

ü  Sending of one or more "end marker" to the source eNodeB, source SGSN or source RNC immediately after switching the path during inter-eNodeB and inter-RAT handover, especially to assist the reordering function in eNodeB.

ü  E-UTRAN idle mode downlink packet buffering and initiation of network triggered service request procedure

ü  Mobility anchoring for inter-3GPP mobility (terminating S4 and relaying the traffic between 2G/3G system and PDN GW).

ü  Lawful Interception

ü  Transport level packet marking in the uplink and the downlink, e.g. setting the DiffServ Code Point, based on the QCI of the associated EPS bearer

ü  Accounting for inter-operator charging. For GTP*-based S5/S8, the Serving GW generates accounting data per UE and bearer.

ü  Interfacing OFCS* according to charging principles

ü  Packet Filtering with TFT*

GTP = GPRS Tunneling Protocol

OFCS = Off-Line Charging System

TFT = Traffic Flow Templete.

                                  

 PGW (PDN Gateway): The PGW is the node that terminates the SGi interface towards the PDN. If a UE is accessing multiple PDNs, there may be more than one PGW for that UE. The PGW provides connectivity to the UE to external packet data networks by being the point of exit and entry of traffic for the UE. The PGW performs policy enforcement, packet filtering for each user, charging support, lawful Interception and packet screening.

ü  PGW provides connectivity towards PDN (eg. Company intranet, internet, and IMS) via SGi Interface.

ü  It is comparable to GGSN

ü  A major functionality provided by a PGW is the QoS coordination between the external PDN and EPC.

ü  PGW can be connected to a PCRF via Gx Interface.

ü  In Local Breakout scenario, PGW transmits and receives packet data from SGW in the same PLMN via S5 interface.

PGW Functions:

ü  Per-user based packet filtering (by e.g. deep packet inspection).

ü  Lawful Interception

ü  UE IP address allocation

ü  Transport level packet marking in the uplink and downlink, e.g. setting the DiffServ Code Point, based on the QCI of the associated EPS bearer.

ü  Accounting for inter-operator charging.

ü  UL and DL service level charging (e.g. based on SDFs defined by the PCRF, or based on deep packet inspection defined by local policy).

ü  UL and DL rate enforcement based on APN-AMBR (e.g. by rate policing/shaping per aggregate of traffic of all SDFs of the same APN that are associated with Non-GBR QCIs)

ü  Packet screening (firewall)

ü  Policy enforcement (gating and rate enforcement)

ü  Mobility anchor for mobility between 3GPP access systems and non-3GPP access systems. This is sometimes referred to as the SAE Anchor function.

                                                

PCRF (Policy & Charging Rule Function)

ü  PCRF is responsible for negotiating QoS policy and charging policy on a per flow basis.

ü  The PCRF major functionality is the QoS coordination between the external PDN & EPC.

ü  The PCRF is connected via Rx+ interface to the external Data network (PDN)

ü  This function can be used to check and modify the QoS associated with SAE bearer setup  from SAE or to request the setup of a SAE bearer  from the PDN.

ü  This QoS management resembles the policy and charging control framework introduced for IMS with UMTS.

PCRF Functions:

ü  Binding mechanism, associates a service data flow to the EPS bearer deemed to transport the service data flow

ü  Reporting, Credit Management, Event Trigger, Termination Action.

ü  Service (data flow) prioritisation and conflict handling

ü  Standardised QoS characteristics

ü  Handling of packet filters.

ü  In non-roaming scenario, there is only a single PCRF in the HPLMN associated with one UE's IP-CAN session. The PCRF terminates the Gx, Gxc and Gxa interfaces.

                                                   

HSS ( Home Server Subscriber):

ü  It was first appeared in 3GPP Release 5 as part of IP Multimedia Subsystem (IMS)

ü  It has similar function to HLR (Home Location Register) and AuC (Authentication Center) in GSM/UMTS network.

ü  In LTE/EPC, the HSS stores data for mobility and service handling per subscriber.

ü  HSS utilizes DIAMETER protocol to support LTE/EPC.

ü  The HSS can be accessed by MME via S6a interface.

For EPS, the HSS data may contain:

ü  IMSI  (International Mobile Subscriber Identity)

ü  IMEI  (International Mobile Station Equipment Identity)

ü  MME Address

ü  EPS subscribed charging characteristics (e.g. prepaid, normal, flat-rate etc.)

ü  Subscribed UE-AMBR. It determines Aggregate Maximum Bit Rate per subscriber

ü  PDN Address

ü  APN (Access Point Name)

ü  EPS Subscriber QoS profile, etc.