EPS network elements Functionality

Functionality of the network elements is grouped in several domains:

UE Domain
Radio Access Network Domain (LTE)
Core Network Domain (SAE)
Service Domain (IMS)


UE Domain 

UE Domain is Consists of  UE and Uu Interface.

USER EQUIPMENT (UE)

The User Equipment allows a user access to network services. For the purpose of 3GPP specifications the interface between the UE and the network is the radio interface.A User Equipment can be subdivided into a number of domains,the domains being separated by reference points. Currently the User Equipment is subdivided into the Universal Integrated Circuit Card (UICC) domain and the Mobile Equipment (ME) Domain. The ME Domain can further be subdivided into one or more Mobile Termination (MT) and Terminal Equipment (TE) components showing the connectivity between multiple functional groups.

UU INTERFACE:

The LTE radio interface is based on OFDM (Orthogonal Frequency Division Multiplex) in DL and SC-FDMA (Single Carrier Frequency Division Multiple Access) in UL. These techniques are well suited for flexible bandwidth operation. This enables operators to deploy LTE in different regions with different frequency bands and bandwidths available. In addition to that, both FDD (Frequency Division Duplex) and TDD (Time Division Duplex) is supported, which opens up for deployment in both paired and unpaired spectrum. In FDD, different frequency bands are used for UL and DL. In TDD the UL and DL transmissions are separated in time.

Radio Access Network Domain (LTE)

Radio Access Network Domain (LTE) is Consists of E-UTRAN

RADIO ACCESS DOMAIN

Radio Access Domain is referred as Evolved UTRAN. It consists only of a number of eNodeBs (eNB) that are interconnected via X2 interface through an IP network. The eNBs are connected by means of the S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME and to the Serving Gateway (S-GW) by means of

the S1-U interface. The S1 interface supports a many-to-many relation between MMEs / Serving Gateways and eNBs.

Evolved Packet System is another naming that group Evolved Packet Core EPC and E-UTRAN. The standard development in 3GPP is grouped into two working groups: Long Term Evolution (LTE) targeting Radio Access Network and System Architecture Evolution (SAE) targeting Core Network.

LTE/SAE naming is commonly used however it is more accurate to use E-UTRA/EPC.

E-UTRAN Node B - eNB
An eNB is a logical network component which serves one or more E-UTRAN Cells. It is responsible for radio transmission and reception from/to UE. Some of eNodeB functionalities are:
• Cell Control and MME pool support:
• Control and User Plane Security
• Segmentation/Concatenation
• Error Correction
• Shared Channel Handling
• Scheduling
• Physical Layer functions such as channel coding, modulation,
filtering
• Handling of Measurement Control/Reporting
• Mobility Control
An eNB can support FDD mode, TDD mode or dual mode operation.

Core Network Domain (SAE) 

Core Network Domain (SAE) is Consists of MME,HSS,S-GW and P-GW.

Core Network Domain is referred as Evolved Packet Core (EPC) and consists of following network elements:


Mobility Management Entity MME
MME is the control plane entity within EPS supporting following
functions:
Mobility Management:
• NAS signalling and security
• Inter CN node signalling for mobility between 3GPP access
networks
• Tracking Area list management
• PDN GW and Serving GW selection
• SGSN selection for handovers to 2G or 3G 3GPP access
networks
• Roaming
• Authentication
• Bearer management functions including dedicated bearer
establishment
• Lawful interception of signalling traffic
• Initiating IMSI detach at EPS detach
• Initiating paging procedure towards eNodeB when MSC pages
the UE for CS services
• Supporting SMS procedures for CS fallback.
• Support CS fallback interface and related functions for CDMA
access.


The Home Subscriber Server (HSS)
The HSS is the master database for an operator. It is the entity containing the subscription-related information to support the network entities actually handling calls/sessions. A Home Network may contain one or several HSSs: it depends on the number of mobile subscribers, on the capacity of the equipment and on the organisation of the network. As an example, the HSS provides support to the call control servers in order to complete the routing/roaming procedures by solving authentication, authorisation, naming/addressing resolution, location dependencies, etc.The HSS is responsible for holding the following user related information:
• User identification, numbering and addressing information
• User security information: Network access control information for authentication and authorization
• User Location information at inter-system level: the HSS supports the user registration, and stores      inter-system location information, etc.
• User profile information. The HSS also generates User Security information for mutual
authentication, communication integrity check and ciphering. Based on this information, the HSS also is responsible to support the call control and session management entities of the different
domains and subsystems of the operator.


Serving GW
The Serving GW is the gateway which terminates the interface towards E-UTRAN.
For each UE associated with the EPS, at a given point of time, there is a single Serving GW.
Some functions of the Serving GW are listed:
• the local Mobility Anchor point for inter-eNodeB handover
• Mobility anchoring for inter-3GPP mobility
• ECM-IDLE mode downlink packet buffering and initiation of network triggered service request          procedure
• Lawful interception
• Packet routing and forwarding
• Transport level packet marking in the uplink and the downlink
• Accounting on user and QCI granularity for inter-operator charging
• A local non-3GPP anchor for the case of roaming when the non-3GPP IP accesses connected to the      VPLMN
• Event reporting (change of RAT, etc.) to the PCRF
• Uplink and downlink bearer binding towards 3GPP accesses
• Uplink bearer binding verification with packet dropping of "misbehaving UL traffic"


Packet Data Network Gateway PDN GW
The PDN GW is the gateway which terminates the SGi interface towards the PDN. The P GW provides PDN connectivity to both GERAN/UTRAN only UEs and E UTRAN capable UEs using any of E UTRAN, GERAN or UTRAN. The P GW provides PDN connectivity to EUTRAN capable UEs using E UTRAN only over the S5/S8 interface. Some of PDN GW functions include:
• Per-user based packet filtering (by e.g. deep packet inspection)
• Lawful interception
• UE IP address allocation
• 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
• UL and DL service level charging, gating control, rate enforcement
• UL and DL rate enforcement based on APN-AMBR
• DL rate enforcement based on the accumulated MBRs of the aggregate of SDFs with the same GBR    QCI (e.g. by rate policing/shaping)
• DHCPv4 (server and client) and DHCPv6 (client and server) functions
• Additionally the PDN GW includes the following functions for the GTP-based S5/S8
• UL and DL bearer binding
• UL bearer binding verification
• The PDN GW functions also includes user plane anchor for mobility between 3GPP access and            non-3GPP access

SERVICE DOMAIN(IMS)

It is connected with P-GW and PCRF. Actually it is PDN (Internet,AF,Application Servers i.e:Skype,Face Book,Yahoo,Google,Youtube etc)

IP Multimedia Subsystem (IMS) is defined by 3GPP/3GPP2 as acore and service 'domain' that enables the convergence of data,speech and network technology over an IP-based infrastructure.
It is the operator choice of control and service logic for primarily IP/packet-based person-to-person communication but also for person-to-content communication. For users, IMS-based services will enable communications in a variety of modes – including voice, text, pictures and video, or any
combination of these – in a highly personalized and secure way. IMS is designed to fill the gap between the existing traditional telecommunications technology and internet technology that
increased bandwidth alone does not provide. This allows operators to offer new, innovative.

LTE / SAE Architecture

UTRAN Long Term Evolution (LTE) refers to the long term evolution of the 3GPP
radio access technology and is considered the successor of the current UMTS
system with the rollout anticipated to begin with trials in 2009.

The LTE work in 3GPP is closely aligned to the 3GPP system architecture evolution
(SAE) framework which is concerned with the evolved core network architecture. The
LTE/SAE framework defines the flat, scalable, IP-based architecture of the Evolved
Packet System (EPS) consisting of a radio access network part (Evolved UTRAN)
and the Evolved Packet Core (EPC).

Note that the Evolved Packet System is purely packet based. Voice transport is thus
based on Voice over IP (VoIP) technology. Circuit-switched (CS) voice traffic is
supported by either using the CS fallback (CSFB) or the single radio voice call
continuity (SR-VCC) interworking solution.

Move your mouse pointer over the items in the architecture figure for a short
introduction to each item.

·  LTE is the evolution towards a flat network architecture.

· The LTE radio interface (air interface, LTE-Uu) is between the user equipment
(UE) and the eNB.

· The evolved Node B (eNodeB, eNB) supports the LTE radio interface and
provides the packet-switched functionality of a traditional radio network
controller (RNC). As a result, the Evolved UTRAN does not require a
separate RNC network element, in other words the architecture is “flat”
(architecture contains fewer types of network entities and interfaces)

· The X2 interface between two eNB network elements is used during an intereNB
handover.

· The S1-MME interface carries control plane signalling information between the
eNodeB and Mobility Management Entity.

· The S1-U interface between the eNodeB and Serving Gateway carries the user
plane data over a so-called GTP tunnel.

· The S4 interface between the S-GW and SGSN provides a GTP tunnel for the
user plane during an inter-system handover.

· The S3 interface carries signalling between the MME and Serving GPRS
Support Node (SGSN) located in a 2G/3G packet-switched core network.

· The S11 interface carries signalling messages between the Serving Gateway
and the Mobility Management Entity.

· The S6a interface is used for transferring subscription and authentication data
between the Home Subscriber Server (HSS) and MME.

The Gx interface is between PGW and PCRF,The PCRF provides policy control decisions and flow based charging controls. The PCRF
determines how a service data flow shall be treated in the enforcement function (PGW in
this case) and ensure that the user plane traffic mapping and treatment is in accordance
with the user’s profile

· The SGi interface is between the PDN Gateway and the packet data network
(PDN). The packet data network may be an operator-external public or private
IP network, or an IP network belonging to the operator, for instance providing
IP Multimedia Subsystem (IMS) services. Legacy Gn/Gp interface
connectivity to the EPS is also supported.

· The Serving Gateway (S-GW) and PDN Gateway (P-GW) provide the user
plane connectivity between the access network and the external packet data
network (PDN). In the Nokia Siemens Networks LTE solution, it is possible to
implement these functional entities within a single node.

· The Mobility Management Entity (MME) provides the basic control plane
functionality in the Evolved Packet Core network. Note that user plane traffic
does not go through the MME.

Evolution of the system architecture from GSM and UMTS to LTE

In 2004, 3GPP began a study into the long term evolution of UMTS. The aim was to
keep 3GPP’s mobile communication systems competitive over timescales of 10 years
and beyond,by delivering the high data rates and low latencies that future users would require.

In the new architecture, the evolved packet core (EPC) is a direct replacement for the packet
switched domain of UMTS and GSM. It distributes all types of information to the user, voice as
well as data,
using the packet switching technologies that have traditionally been used for data alone.

There is no equivalent to the circuit switched domain: instead, voice calls are transported using
 voice over IP. The evolved UMTS terrestrial radio access network (E-UTRAN) handles the EPC’s
radio communications with the mobile, so is a direct replacement for the UTRAN.

The mobile is still known as the user equipment, though its internal operation is very
different from before.

The new architecture was designed as part of two 3GPP work items, namely system
architecture evolution (SAE), which covered the core network, and long term evolution
(LTE), which covered the radio access network, air interface and mobile. Officially, the
whole system is known as the evolved packet system (EPS), while the acronym LTE refers
only to the evolution of the air interface. Despite this official usage, LTE has become a
colloquial name for the whole system, and is regularly used in this way by 3GPP.

Introduction

Hello every one,i started this blog to share my knowledge and experience with the people around.
In this blog i am sharing topics on UMTS,LTE,LTE-A,VoLTE and IMS technologies.

 In order to better understatement of technology for career beginners,students,professors i am starting each technology from it's scratch level.