EPS1 Overview Architecture

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Evolved Packet System

Overview of EPS

Requirements andArchitectural overview


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CONTENT

1. Evolution of Mobile Communications2. Requirements to Evolved Packet System

3. Architectural overview


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Evolution of mobile communications

Evolution of 2G and 3G mobile technologies


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Typical downlink throughput for

2G and 3G technologies

Typical downlink user data

throughput of IS-41 systems


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System Architecture Evolution(SAE) is the name of the3GPP standardization work item which is responsible forthe evolution of the packet core network, more commonly

referred to as EPC.

Evolved Packet System(EPS) covers the radio access,the core network and the terminals that comprise the overall

mobile system. Also provides support for other high-speed

RANs that are not based on 3GPP standards, for example,

WLAN, WiMAX or fixed access.


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Evolution of mobile communicationsSAE building bridges between different networks

1. Support for non-3GPP access networks2. Support handovers between 3GPP and non-3GPP accesses

3. Network-based mobility mechanisms were preferred

4. Common Security framework

5. Common User management and Authentication and Authorizationframework

6. Common Policy and Charging support

7. Common framework for On and Off line Charging and Accounting

8. Provide Optimized handover to/from existing deployed Radio access

and Packet Core networks: GPPs GERAN, UTRAN and HSPA andGPP2s HRPD networks

9. Common Evolved Packet Core for access to Common IMS and

Applications and Service framework

10. Common operations and management of Terminals.


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Evolved Packet System is an evolution of the 3G UMTS

characterized by higher-data-rate, lower-latency, packet-optimizedsystem that supports multiple radio access technologies.

The Evolved Packet System comprises the Evolved Packet Coretogether with the evolved radio access network (E-UTRA and E-UTRAN).

The focus of the EPS work is on enhancement of Packet Switched

technology to cope with rapid growth in IP traffic.


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The Evolved Packet System is characterised by:

Reduced latency

Higher user data rates equating to broadband performance

(peak packet data rates of100 Mbps on the radio access bearerdownlink to the UE and 50 Mbps on the uplink)

Improved system capacity and coverage

Lower operational costs

E-UTRAN latency requirements


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The objectives of the EPS are to:

Provide higher data rates, lower latency, high level of security and

enhanced QoS;

Support access system selection based on a combination of

operator policies, user preference and access network conditions;

Realise improvements in basic system performance whilst

maintaining the negotiated QoS across the whole system;

Provide capabilities for co-existence with legacy systems and

migration to the EPS;

Support a variety of different access systems (existing and future),ensuring mobility and service continuity between these access

systems.


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Internet

and

E-UTRAN

EvolvedPacketCore

SC

MM

AAA

Policy

AccessSystem

PSTN

. . .

EvolvedPacketSystem. . .

E-UTRANon 3GPP

3GPPLegacy

System . . .

Heterogeneous access system mobility between 3GPP

Legacy Systems or E-UTRAN and non 3GPP Access

Systems including Fixed Access systems


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Requirements to EPSHigh-level requirements user and operational aspects

Enhanced performance e.g., low communication delay, low

connection set-up time and high communication quality;

Efficiently support a variety of traffic models e.g. user-to-user,

user-to-group and traffic models generated by ubiquitous services;

Always on

The support for efficient

mechanisms to support

always-connected terminals is

a key requirement for serviceslike Presence, Instant

Messaging and Push-To-Talk.

Terminal state transition requirements


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Requirements to EPSHigh-level requirements user and operational aspects

Support of service continuity between 3GPP access systems

and also between 3GPP access systems and non 3GPP access

systems whether the UE supports simultaneous radio transmission

or not.

Service Continuity: The uninterrupted user experience of a servicethat is using an active communication (e.g. an ongoing voice call)when a UE undergoes a radio access technology change or a

CS/PS domain change without, as far as possible, the user noticing

the change.

Service capability set shall include, as a minimum, support for thefollowing categories of services :

- Voice

- Video

- Messaging

- Data file exchange


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Requirements to EPSQuality of Service

Network

Access

Service

Access

Service

Integrity

Service

Retainability

Phases of service use from customer's point of view

Network Access: The network indication on the display of themobile is a signal to the customer that he can use the service of this

network operator (or any other means to indicate to the user that a

network is available).

Service Access: If the customer wants to use a service, the network

operator should provide him as fast as possible access to the service.Service Integrity: This describes the Quality of Service duringservice use.

Service Retainability: Service retainability describes the terminationof services (in accordance with or against the will of the user).


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Requirements to EPSQuality of Service

There should be no perceptible deterioration ofaudio quality of avoice call during and following handover between dissimilar CS and

PS access networks, and transitions between PS access networks

supporting different IP protocol versions.

There should be no loss of data, as a result of handovers between

dissimilar fixed and mobile access systems, including those thatsupport different versions of the IP protocol.

The EPS network shall support a minimum of 8 levels of QoS in

parallel.

It shall be possible for the EPS to change QoS, when the terminal

moves from one access system to a new access system and thenew access system can not provide the same QoS as the old

access system or the new access system can provide higher QoS.


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Requirements to EPSSupport of Multicast and Broadcast Services

The EPS shall be able to support Multicast and BroadcastServices which shall be enhanced especially from some aspects,

e.g. optimized service provisioning procedures, better performance

compared to current MBMS system, and support of multiple access

systems.

Support of Emergency Calls

The EPS shall support IMS emergency calls applicable to the PS

domain


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Requirements to EPS

The EPS shall provide a high level of security. Any possible lapse insecurity in one access technology shall not compromise security of other

accesses.

The EPS should provide protection against threats and attacks

including those present in the Internet.

The EPS shall support information authenticity between the terminal

and Evolved Packet Systems.

The EPS shall allow for a network to hide of internal network elements

from the UE.

Security policy shall be under the control of the home operator. Appropriate traffic protection measures should be provided by the EPS

The EPS shall provide appropriate mechanisms to enable lawful

intercept.

Security requirements


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Architecture overview


Pure IP infrastructure supporting the logical nodes with functions needed forIP connectivity

and routing between the entities, DNS functions supporting selection and discovery of different

network elements, support forboth IPv4 and IPv6 in the transport and application layer.


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Architecture overviewBasic IP connectivity over LTE access

Basic EPS architecture for LTE

Two main principles have been guiding

the design of the architecture:

to optimize the handling of the user

data traffic itself, through designing a

flat architecture (as few nodes aspossible are involved in processing the

user data traffic).

to separate the handling of the control

signaling from the user data traffic.


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Architecture overviewBasic IP connectivity over LTE access

Basic EPS architecture for LTE

eNodeB (the LTE base station) -

includes all features needed to realize the

actual wireless connections between user

devices and the network.

Mobility Management Entity (MME)

handles all LTE-related control plane

signaling, including mobility and security

functions for devices and terminals

attaching over the LTE RAN.

The user data payload are handled by

two logical nodes called the Serving

Gateway (Serving GW) and the Packet

Data Network Gateway (PDN GW).

HSS manages user data and related

user management logic for users

accessing over the LTE RAN.


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Architecture overviewAdding more advanced functionality for LTE access

Adding policy and charging control to the basic EPC architecture

The PCC (Policy and Charging

Control) concept is designed to

enable flow-based charging,

including, for example, online

credit control, as well as policy

control, which includes support forservice authorization and QoS

management.

PCRF contains policy control

decision and flow-based charging

control functionalities.


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Charging models supported by the EPS include:

- calling party pays

- charging based on assured QoS

- charging based on the transport

- charging based on an event

- charging based on content

- charging adjustment (e.g. based on subscription bands)- alternate party charging.

Charging mechanisms of the EPS provide:

- Cost effective Control and Charging of IP Flows

- Perform online charging- Support differentiated charging including zero rating of the

bearer and event charging

- Awareness of subscriber identity, time-of-day, roaming status,

QoS, Service input etc.



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Adding policy and charging control to the basic EPC architecture

OFCS - Offline Charging System

OCS - Online Charging System.

Both logical entities interface the

PDN GW (through the Gz andGy interfaces respectively) and

support various features related to

charging of end users based on a

number of different parameters

such as time, volume, event, etc.


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Architecture overviewInterworking between LTE and GSM/GPRS or WCDMA/HSPA

Before EPS, when the user has moved

and wants to use the new access

network, the network considers this as a

completely new attach request.

The device is normally given a new IPaddress from the network, which then

may or may not cause problems for the

applications in use in the device.

Furthermore, there is normally a quitelong service interruption between loss of

coverage of network A and the

establishment of IP connectivity to

network B.Inter-access mobility without

session continuity


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The EPC architecture allows for session

continuity, that is that an IP connectivity

session which is established over any of

the allowed access networks (A or B)

actually will survive movements between

the different access networks due to lossof radio coverage.

This is handled through retaining a stable

IP anchor point in the network which

allows fornot having to change the IPaddress of the device at all. Applications

and services will, in theory, then not be

dependent on the access network that is

in use or on any possible movements

between these.

Inter-access mobility with

session continuity


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Interworking between LTE and GSM/GPRS or WCDMA/HSPA

The interworking solution forLTE includes the SGSN attaching

to GSM and WCDMA radio

networks as today, but then

includes the MME and the PDN

GW acting as an SGSN and aGGSN respectively.

The MME and PDN GW are in

fact replicating the signalling

needed for movements betweennetworks GSM/GPRS and

WCDMA/HSPA to also apply for

mobility with LTE.

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SGSN distinguishes a terminal- that attaches over GSM/GPRS or

WCDMA/HSPA but is not capable of

moving to LTE

- that in fact can connect to LTE but

is currently attaching to GSM/GPRS

or WCDMA/HSPA due to lack of LTE

radio coverage.

The latter terminal must always be

using the PDN GW as the anchor

point and never a GGSN since thereis no logical connection between the

LTE radio network and a GGSN.

Interworking between LTE and GSM/GPRS or WCDMA/HSPA

SGSN selecting GW


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Interworking using GTPv2 interfaces

The SGSN implements fournew interfaces.

S3, S4 and S16 rely on an

updated version of the GTP

protocol and are usedinstead of the different

variants of the Gn interface.

S6d - data related to GSM

and/or WCDMA, not to LTE.


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Interworking using GTPv2 interfaces

S4 - creates a common anchorpoint for LTE, GSM/GPRS and

WCDMA/HSPA in the Serving

GW.

S3- signaling-only interfaceand supports inter-systemmobility.

S16 - mimics the MME S6a

interface towards the HSS for

retrieving subscriber data from

the HSS.


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Direct tunnel support for WCDMA/HSPA

S12 (optional for user traffic)- utilizes a direct connection

between the RNC in the

WCDMA radio network and

the Serving GW.

If S12 is used, the SGSN will

only handle the control

signaling for WCDMA/HSPA.

The primary driver for this isthat the network does not

have to be scaled in terms of

SGSN user capacity.


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Architecture overviewInterworking between LTE and CDMA networks

Interworking between LTE and eHRPD networks

Efficient and smooth

handovers between the

different technologies:

Access authentication for a

user attaching over aneHRPD network are based on

AAA functionality (a software

feature inside the HSS or

stand-alone AAA equipment

interfacing the HSS over theDiameter-based SWx

interface).


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Architecture overviewInterworking between 3GPP access technologies and

non-3GPP access technologies

Interworking between 3GPP access and


Terminals IP address assignment,

access to general IP services as

well as network features like user

subscription management,

security, charging, policy controland VPN connections are

independent of the access

technology be it wireless or

fixed.


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There are two ways to distinguish between the available options:

1. Are Network-based or Client-based mobility mechanisms used?

2. Is it a connection to trusted or a non-trusted network?

Network-based means that there are functions in the access network

that acts on behalf of the terminal, and provides mobility support. It

simplifies the terminal client application, but instead requires that

there is specific Mobile IP support in the network itself.

Client-based approach works over any access network, as long as

there is adequate support in the terminal itself. This function may be

used totally transparent to the functionality in the access network.


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There are two ways to distinguish between the available options:

1. Are Network-based or Client-based mobility mechanisms used?

2. Is it a connection to trusted or a non-trusted network?

An indicator on if the 3GPP operator (owning the PDN GW and theHSS) trust the security of the non-3GPP access network

A typical trustednetwork may be an eHRPD network, while a non-

trusted network may be, for example, usage of WLAN in a publiccaf and connecting to the PDN GW over the public Internet.


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EPC architecture for non-3GPP accesses

ePDG (evolved Packet

Data Gateway) is an

evolution of the PDG that

is specified in earlier

versions of the 3GPPstandards to allow

interconnection (but not

inter-access mobility) of

WLAN access to a 3GPP

network. Typically, the

ePDG belongs to the

mobile operator.

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EPC architecture for non-3GPP accesses

Encrypted tunnels are

established between the

user devices and the

ePDG, to ensure that

each device cancommunicate with the

network in a secure way.

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Architecture overviewSupport for voice services

EPC architecture for voice support

Specific mechanisms to allow for

voice services for users of the

packet data services offered over

the LTE access:

IMS mechanisms realizing voice

using the MultiMedia Telephony(MMTel)user device cant

encounter the lost of LTE

coverage.

stick to the old CS way ofproviding voice services. Users

temporarily leave LTE to perform

the voice calls over 2G/3G, and

then return when the voice call is

finished.

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Architecture overviewSupport for voice services

EPC architecture for voice support

Sv interface forIMS solution:

-Single-Radio Voice Call Continuity(SRVCC).

SGs interface (no IMS)

- Circuit-Switched Fallback (CSFB).

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Architecture overviewMiscellaneous features

Miscellaneous features in the EPC

architecture

ETWS ( Earthquake and

Tsunami Warning System)

Warnings from Cell Broadcast

Centre (CBC)

MMEs must convey the warningsto all terminals that happen to be in

idle mode, and whose location is

only known with the accuracy of a

Tracking Area.

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Architecture overviewMiscellaneous features

Miscellaneous features in the EPC

architecture

Equipment Identifier Register

(EIR)

ANDSF ( Access Network

Discovery and Selection Function)

- used to control how users and

their devices prioritize betweendifferent access technologies if

several non-3GPP access

networks are available. It is a

means to give the network

operator the possibility to controlhow users attach to the network,

based on a number of criteria.

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Overall EPS architecture

EPS1 Overview Architecture

Documents