eps - introduction and architecture - slides.pdf

EVOLVED PACKET SYSTEM

Introduction and Architecture

F. Edler / June 2010 2

What is the Evolved Packet System?

EUTRAN EPC

EPS

+

New mobile network system

Two parts

– Radio access network: eUTRAN

(Evolved UMTS Terrestrial Radio Access Network

– Evolved packet core: EPC


Mobile network evolution

Two 3GPP working groups:

– LTE (Long Term Evolution): EUTRAN

– SAE (System Architecture Evolution): EPC

Three limiting factors today:

Data rates: 14 Mbits / 5,7 Mbits 50 - 100 Mbits

Delay: 50 - 100 ms below 10 ms

Architecture: 2 networks (CS+PS) 1 network (PS)


Further motivations for network evolution

Requirements

– Rapid growing of IP traffic

– High performance with

reduced cost

– Seamless mobility

Solution

– HSDPA/HSUPA/HSPA+

LTE (higher efficiency)

– By flat architecture and

avoiding unnecessary

nodes and interfaces

– including also IETF based

protocols


Building blocks of EPS

OFDMAOFDMA

Multiple

Antenna

Techniques

Very high

spectral

efficiency

Air Interface

OFDMADistributed

IP based

Reduced

Latency,

Scalability

Radio Network

Architecture

OFDMAIMS

IP based

Scalability,

Cost efficiency,

Services

Core Network

Evolved

Packet

Systen

Three areas of enhancements:


Evolution of data rates

1990s 2000 2003 2006 2007 2008+

Maximum 56k 473k 14M DL 5,7M UL 42M / 11,4M

Advertised 14k 60 – 80k 400 -700 k tbd tbd

GSMGPRS/

EDGE

UMTS/

HSDPA

UMTS/

HSUPA

UMTS/

HSPA+

Maximum 115k 614k 2,45M DL 3M / 1,8M

Advertised 14k 60 – 80k 400 -700 k 400k – 800k

IS-95 1xEV-DO

Rev 0

EV-DO

Rev A

LTE is sometimes called 4G technology, but

– ITU has defined 4G: peak data rates up to 1 GB

– 3GPP actually works on “LTE Advanced” as a 4G candidate


EPS overview

eNodeB

EUTRAN EPC

EPS

EUTRAN- eNodeB

- reduced number of nodes

- OFDMA

- SC-FDMA

- adaptive modulation

(up to 64 QAM)

EPC- all IP

- interworking with 3GPP

and non 3GPP networks

- More efficient QoS and

security

MME

P-GWS-GW

HSS

Reduced network complexity!

Compare with 2G/3G architecture (next slide)


EPS overview (some more details)

Reduced network complexity!

Compare with 2G/3G architecture (next slide)

EPC

S1-U

S6a

S11

S5/S8

External

Data

Networks

(PDNs)

SGi

eNodeB

LTE

S-GW

MMEHSS

P-GW


2G/3G network architecture

GSM radio network

(GERAN)

UMTS radio network

(UTRAN)

BSC

RNC

MSC/

VLR

SGSN

A

Gb

Iu-PS

Iu-C

S

GGSN

External

Voice

Network

External

Data

Networks

BTS

NodeB

GMSC

BTS Base Transceiver Station

MSC Mobile Switching Center

GMSC Gateway MSC

RNC Radio Network Controller

SGSN Serving GPRS Support Node

GGSN Gateway GPRS Support Node

GERAN GSM EDGE Radio Access Network

UTRAN UMTS Terrestrial Radio Access Network

CS-CN

PS-CN

HLR

HLR


Voice services in EPS

EUTRAN EPC IMS

IMS signalling and session data

All services are packet-switched

Also voice calls have to be handled natively by VoIP and IMS

Signalling and media are transparently carried through EPS

Is IMS required for EPS introduction?

– In principle yes, but there are workaround solutions: a) CS Fallback b) VoLGA


Seamless mobility and all-IP convergence

Services

(e.g. IMS)

All-IP Core (EPC)

WLAN

Hot-Spots

UTRAN

GERANEUTRAN WiMAX

Integrated network (all IP) enables

– Cost reduction

– Integrated multimedia services

– Seamless mobility between networks


EPS main requirements

Main EPS

requirements

Low latency

Decreased Complexity

- No CS-core-network

- Direct Link between core

and NodeB

Good QoS support

Enhanced security

Further features:

– Network sharing: eUTRAN broadcasts PLMN ID

– Distributed architecture

– Common evolution for 3GPP and 3GPP2


EPS architecture

S1-U

S1-MME S11

S5/S8

External

Packet Data

Network

(PDN)eNodeB

eUTRAN

LTE

S6a

EPC

PCRF

HSS

ePDG

MME

P-GWS-GW

Strict separation between data and signalling path

– Signalling: eNodeB – MME – S-GW – HSS – PCRF

– Data: eNodeB – S-GW – P-GW - ePDG


Mobility Management Entity (MME)

Manages and stores user context data information

– IMSI (International Mobile Subscriber Identity)

– UE network capability

Generates temporary identifiers for the UEs: GUTI *

Manages mobility during handovers

Manages sessions: EPS bearer set-up and tear down

Distributes paging messages

Cares for security: authentication, encryption, integrity prot.

* Globally Unique Temporary Identity


Serving Gateway (S-GW)

PDN Gateway (P-GW)

S1-U S5

External

Packet Data

Networks

(PDN)

eNodeB

SGi

· Data Forwarding

· Inter-3GPP mobility anchor

· Gateway to PDNs

· Inter-technology mobility anchor

· IP address allocation

· Data rate enforcment

S-GW P-GW

S-GW and P-GW

– handle the user traffic only (scalability)

– are sometimes implemented in one network node


Home Subscriber Server (HSS)

Contains the user database

– Subscription related data (authentication data)

– Service profile

Communicates with MME

Maybe combined with HSS of IMS


Evolved Packet Data Gateway (ePDG)

untrusted

non-3GPP

access

network

EPC

P-GW

ePDG

Tunne

ling

For interworking with “untrusted non-3GPP” access networks

User connects to IP address of ePDG and authenticates

After that an IPsec tunnel is set-up


Policy Charging Rule Function (PCRF)

S5/S8

PCRF

P-GW

External

Packet Data

Network

(IMS)

P-CSCF

SGi

In IMS signalling and media data are separated

EPS transports signalling and media

PCRF controls data connections in EPS (EPS bearers)

The applications (P-CSCF) interact with PCRF

PCRF controls P-GW, in some cases also the S-GW


Evolved Node B (eNode B)

LTE-Uu

S1 S1 S1

Evolved Packet

Core

X2

X2X2

· Radio Resource Management

· Radio Handover Management

· Call Admission Control

· Latency Reduction

Flat architecture reduces latency

eNodeBs are also connected with each other (X2)

Upstream connection via S1-MME and S1-U

S1 interface: many-to-many connection for redundancy/loadsharing


Tracking concept

TA e

TA b

TA x

. . .eNB1

eNB2

Tracking Area 2

Tracking Area 1

TA x

TA y

TA z

. . .

UE1

UE2

– In active mode: network knows the position of the UE

– In idle mode: position update only when UE leaves the list of

assigned Tracking Areas

– TA list may be individually assigned


Distributed architecture, redundancy

Tracking Area 1

Tracking Area 2

Tracking Area 3

Tracking Area 4

Tracking Area 5

MME 1 MME 2

MME Pool 1

S-GW 1

Service Area 1

S-GW 2

MME 3 MME 4

MME Pool 2

S-GW 3

Service Area 2

S-GW 4

– EPS characteristic: Many-to-many relationship between nodes

for redundancy and loadsharing

– MME pools and Service areas


EPS interfaces and protocols

SGi

LTE-Uu

S6a

S1-U

S5 PDN

eNodeB

UE

S1-MM

E

S11

X2

S1-U

S1-M

ME

S-GW

MMEHSS

P-GW

– S1-MME: for bearer management in combination with S11

– S1-U: User Data

– S5: User data and bearer management (GTP or PMIPv6)

– NAS (Non Access Stratum) protocol:

between UE and MME for mobility and session management


Life cycle of a mobile

UE powers on: frequency and time synchronisation

UE picks a network and connects with a cell

UE registers with the network

UE gets assigned a default EPS bearer (always on IP)

If some services need a better QoS

dedicated EPS bearers are added

If necessary mobility procedures during active sessions

UE deregisters and powers off


Registration

and

Authentication eNodeBUE

Network discovery

Access system selection

RRC connection establisment

Initial attach

S1 signalling bearer set up

MME selection

Authentication

S-GW and P-GW selection

Default bearer set up

IP address allocation

S-GWMME HSSP-GW


Initial Attach

eNodeBUE

Initial Attach Request

IMSI

UE network capability

PDN address allocation

PLMN ID

MME Pool

PLMN ID

eNodeB picks an

MME based on PLMN

ID and load

MME 1

MME 2

MME 3

– UE sends an initial Attach Request to eNodeB

– eNodeB selects MME


Authentication UE

Authentication Request

(IMSI)

Authentication Response

(IMSI, RAND, XRES, AUTN

KASME)

Authentication Request

(RAND, AUTN)

Stores KASME and XRES

Generates KASME, AUTN

and RES using K and RAND

Checks if generated AUTN is

equal to received AUTN

Authentication Response

(RES)

Checks if received RES is

equal to XRES

MME HSS

– EPS AKA procedure

– Similar to IMS AKA

– Based on a key K

shared by UE and HSS

– RES: to verify UE

– AUTN: to verify network

– KASME: to generate keys

for encryption and

integrity protection


Security

Access Stratum (AS) messages: between UE and eNodeB;

example: RRC (Radio Resource Control)

Non Access Stratum (NAS) messages: between UE and MME

example: handover messages

AS and NAS messages are integrity protected and encrypted

User plane messages: between UE an S-GW are only

encrypted


Selection of security algorithm

UE

NAS Security Mode CMD

(selected algorithms)

NAS Security Mode Complete

MME selects NAS integrity

and security algorithms

eNodeB

UE stores the

selected algorithms

eNodeB selects RRC and user

plane security algorithms

AS Security Mode CMD

(selected algorithms)

AS Security Mode Complete

UE stores the

selected algorithms

MME

– Security algorithms

are selected by

MME and eNodeB


Subscription data and location update

Update Location

Insert Subscriber Data

(List of all APNs, Default APN)

The MME selects the P-GW that serves the default APN

The MME selects the S-GW that supports all the services of the UE

Insert Subscriber Data Ack

MME HSS

– MME updates location

and its identity to HSS

– Access Point Names:

all networks permitted

for UE

– P-GWs are selected

according to APNs

– Only default APN is

enabled at start-up

(default EPS bearer)


Default bearer setup

eNodeBUE

Store S-GW addr and TEID

Create default

bearer request Create default

bearer request

(S-GW TEID)

Create default

bearer response

(P-GW TEID,

IP-addr of UE)

Create default

bearer response

(S-GW TEID

towards eNodeB)

S5

S1 Control msg:

S-GW addr, TEID

(Attach accept,

GUTI, IP addr)

TEID: Tunnel Endpoint Identifier

GUTI: Globally Unique Temporary Identity

RRC Control msg:

default radio-b. info

(Attach accept,

GUTI, IP addr)

RRC Control msg:

(Attach complete)

Default radio bearer

S1 Control msg:

eNodeB addr, TEID

(Attach complete) Update bearer req.

(eNodeB addr.

and TEID)

Default S1-U bearer

Update bearer resp.

MME S-GW P-GW

– MME controls the set-up

of bearers

– IP-address is provided by

P-GW

– The default bearer offers

only default QoS

– An EPS bearer consists of

3 parts:

- S5 bearer

- Radio bearer

- S1-U bearer


Service data flows

Service Data Flow (SDF): main term for set-up of

connections with specific QoS

Service Data Flows with specific QoS are mapped to

dedicated EPS bearers

EPS bearers are characterized by their QoS

More than one SDF may be mapped to an EPS bearer if

same origin and destination


Multiple PDN connections

UE

EPS

PDN 1

PDN 2

PDN 3IP addresses

- A user may subscribe to multiple PDN connections

- PDNs are identified by an APN (e.g. „Internet“)

- a default APN is part of the user subscription information in HSS

P-GW 1

P-GW 2

– Example PDNs: Internet, IMS, corporate networks

– Simultaneous attachments (with different IP addresses) possible


Services and Service Data Flows

UE

EPS

QoS ?

Backhaul

Network

QoS ?

PDN

QoS ? Application

Server

P-GW

Service Data Flow

– Service: Application shared between UE and Application Server

– Identified by IP-addresses, port number and protocol

– QoS is influenced by three different networks

– Service Data Flow:

Characterizes the end-to-end data flow

Defined by packet filters


Service Data Flows and EPS bearers

EPS

P-GW

UE

EPS bearer 1

SDF 2

SDF 1

EPS bearer 2

SDF 3

AS1

AS2

AS3

- A PDN connection may support more then one bearer

- A Service Data Flow has a defined QoS charcteristic

- An EPS bearer is the level where QoS is enforced

- SDFs may be aggregated into the same bearer


Bearer mapping and classification

UE

S1 BearerRadio Bearer S5 Bearer

Upstream:

UE maps SDF to

Radio Bearer

eNodeB maps

Radio Bearer to

S1 Bearer and

vice versa

S-GW maps

S1 Bearer to

S5 Bearer and

vice versa

Downstream:

P-GW maps SDF

to S5 Bearer

S-GW P-GWeNodeB

– Three parts of an EPS bearer only in case of GTP protocol on S1, S5

– Packet classification is done

by P-GW for downstream flow

by UE for upstream flow

– eNodeB and S-GW do only mapping of packets into bearers


QoS and bearer classes

· QCI

· ARP

· GBR

· MBR· AMBR

GBR bearers Non-GBR bearers

QCI QoS Class Identifier

ARP Allocation and Retention Priority

GBR Guaranteed Bitrate

MBR Maximum Bitrate

AMBR Aggregate Maximum Bitrate

– Two main types of QoS classes: GBR and Non-GBR

– 9 QoS classes are defined characterized by a few parameters

(simplified in comparison to 14 parameters in UMTS)

– ARP is used to resolve congestion situations

– AMBR is defined to avoid accumulating of resources


QCI classes QCI Bearer

Type

Application Example Packet

Delay

Packet

Loss

Prio

rity

1 GBR Conversational VoIP 100 ms 10-2 2

2 Conversational Video (Life Streaming) 150 ms 10-3 4

3 Non-Conversational Video (Buffered Streaming) 300 ms 10-6 5

4 Real Time Gaming 50 ms 10-3 3

5 Non-GBR IMS Signalling 100 ms 10-6 1

6 Voice, Video, Interactive Games 100 ms 10-3 7

7

Video (Buffered Streaming)

TCP Apps (web, e-mail, FTP)

Platinum vs. Gold User

300 ms 10-6 6

8 8

9 9

– Packet loss rate refers to air interface in non-congestion situation

– Implementation of QCI classes is operator specific


QoS methods in IP networks

QoS in IP Networks

Integrated Service

(IntServ)

Differentiated Service

(DiffServ)

· Reserve resources throughout the

network for every user

· Used with RSVP signalling

· Optional in EPS

· Classify user packets into a small set

of classes

· Mandatory in EPS

DiffServ is highly scalable and therefore mandatory for EPS

no state information in networks

only relative QoS treatment possible (DSCP codepoints in IP packet header)

QoS method is also important for backhaul networks


Service addition – dedicated bearer setup

EPS

P-GW

PDN

CSCFAS

INVITE INVITE

SDP negotiationSDP negotiation

EPS Bearer Creation

UE


PCRF links SDF and EPS bearers

EPS

P-GW

PDN

CSCFVideo

streaming

server

PCRF

Rules required to create the

EPS bearers for the video

streaming service

Session information

based on SDP

UE

– Inside of EPS the setup of a dedicated bearer is initiated by P-GW

– P-GW S-GW MME

– MME eNodeB


Setup of a dedicated EPS bearer

S-GW P-GW

AS

QoS policy

Application level signalling and media negotiation

eNodeB

MME

PCRF

Apply policies

Create new bearer request

Apply admission control

RRC procedures

Create new bearer response

S1 - bearerRadio bearer S5 - bearer

UE


PMIPv6 based bearer setup

EPS bearer

S1 BearerRadio Bearer

S-GW P-GW

eNodeB

GRE tunnel

to P-GW

S-GW maps SDF

to/from S1-bearer P-GW maps SDF

to/from GRE tunnel

SDF

UE

– Inclusion of non-3GPP access networks via PMIPv6 protocol

– PMIPv6 does not support QoS classification

– No SDFs between S-GW and P-GW

– Downstream classification has to be done by S-GW

eps - introduction and architecture - slides.pdf

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