SAE and Evolved Packet Core

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SAE and Evolved Packet

Core

Farooq Bari

Seattle Communications (COM-19) Society Chapter Nov. 13, 2008

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SAE/EPS Background

Around 2005, 3GPP RAN groups initiated the LTE work and in

parallel the SAE work was started in SA2 to address the system and core network aspects

Main Objectives

To ensure competitiveness of the 3GPP systems in a time

frame of the next 10 years and beyond

to enhance the capability of the 3GPP system to cope with

the rapid growth in IP data traffic

A mechanism to support seamless mobility between

heterogeneous access networks

Important parts of such a long-term evolution included reduced

latency, higher user data rates, improved system capacity and coverage, and reduced overall cost for the operator

A key aspect of SAE vision was “flat IP Architecture” and the

new LTE/SAE system was to be packet only system

Migration aspects were to be taken into account for the above,

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Brief status of Work

3GPP SA2 SAE/EPS work resulted in two new

stage 2 technical specifications:

TS 23.401:GPRS Enhancements for E-UTRAN Access

TS 23.402:Architecture enhancements for non-3GPP

accesses

In addition several other specifications (e.g. TS

23.203 for policy Control and Charging) were

updated to accommodate EPS architecture.

Stage 2 completed June 2008

Target completion date for stage 3 is December

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Evolved Packet System:

EPC & EUTRAN

Evolved Packet System (EPS) provides IP connectivity using the

EPC and E-UTRAN.

High Level Functions of EPC

Network Access Control Functions

Packet Routeing and Transfer Functions Mobility Management Functions

Security Functions

Radio Resource Management Functions Network Management Functions

Covers both roaming and non-roaming scenarios and covers all

aspects, including mobility between E-UTRAN and pre-E-UTRAN 3GPP radio access technologies, policy control and charging, and authentication

Local breakout of IP traffic via the visited PLMN is supported,

when network policies and user subscription allow it. Local breakout may be combined with support for multiple

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TS 23.401

GPRS Enhancements for

E-UTRAN Access

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Non-Roaming Architecture

Ref: TS 23.401 SGi S12 S3 S1-MME PCRF Gx S6a HSS Operator's IP Services (e.g. IMS, PSS etc.)

Rx S10 UE SGSN LTE-Uu E-UTRAN MME S11 S5 Serving Gateway PDN Gateway S1-U S4 UTRAN GERAN SGi S12 S3 S1-MME PCRF Gx S6a HSS Operator's IP Services Rx S10 UE SGSN LTE-Uu E-UTRAN MME S11 S5 Serving PDN S4 UTRAN GERAN

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Key Evolved Packet Core Entities

Mobility Management Entity (MME)

MME is similar in function to control plane of legacy SGSN. It

manages mobility aspects in 3GPP accesses such as gateway selection, tracking area list management etc.

Serving Gateway (SGW)

SGW terminates the interface towards E-UTRAN. It is the local

mobility anchor point for inter-eNodeB handovers and also

provides an anchor for inter-3GPP mobility. Other responsibilities include lawful intercept, charging and some policy enforcement.

Packet Data Network Gateway (PGW)

PGW terminates the SGi interface towards the PDN. It is the key

node for policy enforcement and charging data collection. It also provides the anchor point for mobility with non-3GPP accesses.

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GW selection process

PDN GW selection function:

The PDN GW selection function allocates a PDN GW that shall

provide the PDN connectivity for the 3GPP access

The function uses subscriber information provided by the

HSS and possibly additional criteria. For each of the subscribed PDNs, the HSS provides:

an IP address of a PDN GW and an APN, or

an APN and an indication for this APN whether the allocation of a

PDN GW from the visited PLMN is allowed or whether a PDN GW from the home PLMN shall be allocated.

Serving GW selection function

The Serving GW selection function selects an available Serving

GW to serve a UE

The selection based on network topology

Other criteria for Serving GW selection include load balancing

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PCRF

PCRF is the policy and charging control element

In non-roaming scenario, there is only a single PCRF in

the HPLMN associated with one UE's IP-CAN session

In a roaming scenario with local breakout of traffic there

may be two PCRFs associated with one UE's IP-CAN

session

H-PCRF that resides within the H-PLMN

terminates the Rx reference point for home network services terminates the S9 reference point for roaming with local

breakout

V-PCRF that resides within the V-PLMN

terminates the Gx and S9 reference points for roaming with local

breakout

terminates Rx for roaming with local breakout and visited

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Roaming Architecture 1

Roaming architecture for 3GPP accesses. Home routed traffic

S6a HSS S8 S3 S1-MME S10 UTRAN GERAN SGSN MME S11 Serving Gateway UE “LTE-Uu” E-UTRAN S12 HPLMN VPLMN PCRF Gx Rx SGi Operator’s IP Services (e.g. IMS, PSS etc.) PDN

Gateway

S1-U

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Roaming Architecture 2

Roaming architecture for local breakout, with home operator's application functions only Ref: TS 23.401 S6a HSS S5 S3 S1- MME S10 GERAN UTRAN S G SN MME S11 Serving G ateway UE "LTE-Uu" E - UTRAN S4 HPLMN VPLMN V - PCRF Gx SGi PDN G ateway S1- _U H - PCRF S9 Home Operator’s IP Services Rx

Visited Oper ator

PDN

S12

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Roaming Architecture 3

S6a HSS S5 S3 S1-MME S10 UTRAN S GSN MME S11 Serving G ateway UE “LTE-Uu” E- UTRAN S4 HPLMN VPLMN V -PCRF S7 SGi PDN Gateway S1-U H -PCRF S9 Home Operator’s IP Services Rx+ GERAN S12

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SAE QoS Concepts

The EPS bearer

For E-UTRAN access to the EPC the PDN connectivity service is provided by an EPS bearer in case of GTP-based S5/S8, and by an EPS bearer concatenated with IP connectivity between Serving GW and PDN GW in case of PMIP-based S5/S8

An EPS bearer is the level of granularity for bearer level QoS control in the EPC/E-UTRAN

The initial bearer level QoS parameter values of the default bearer are assigned by the network, based on subscription data

The decision to establish or modify a dedicated bearer can only be taken by the EPC, and the bearer level QoS parameter values are always assigned by the EPC

Bearer level QoS parameters

The bearer level (i.e. per bearer or per bearer aggregate) QoS parameters are QCI, ARP, GBR, MBR, and AMBR

Each EPS bearer is associated with the following bearer level QoS parameters:

QoS Class Identifier (QCI);

Allocation and Retention Priority (ARP).

Each GBR bearer is additionally associated with the following bearer level QoS parameters:

Guaranteed Bit Rate (GBR); Maximum Bit Rate (MBR).

Each APN is associated with an Aggregate Maximum Bit Rate (APN AMBR). Each UE is associated with UE Aggregate Maximum Bit Rate (UE AMBR).

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The EPS bearer with GTP-based

S5/S8

Serving GW PDN GW

eNB

Radio Bearer _{S5/S8 Bearer}

Application / Service Layer

UL-TFT →RB-ID

DL Service Data Flows DL-TFT DL-TFT → S5/S8a-TEID RB-ID ↔S1-TEID

S1 Bearer

S1-TEID ↔S5/S8a-TEID

UE

UL Service Data Flows UL-TFT Serving GW PDN GW eNodeB - → -- → -- ↔ - - ↔ -UE

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Support for multiple PDNs and local

breakout

Multiple PDN support:

Simultaneous exchange of IP traffic to multiple PDNs is supported in

the EPS, when the network policies and user subscription allow it

It shall be possible to support in the EPS simultaneous exchange of

IP traffic to multiple PDNs through the use of separate PDN GWs or single PDN GW

The EPS also supports an UE-initiated connectivity establishment to

separate PDN GWs or single PDN GW in order to allow parallel access to multiple PDNs

Support of Local Breakout

Local breakout of IP traffic via the visited PLMN is supported,

when network policies and user subscription allow it

Local breakout may be combined with support

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Inter-working with Legacy 3GPP

systems

Roaming and inter access mobility between Gn/Gp 2G and/or 3G SGSNs and an MME/S-GW are enabled by:

- Gn functionality as specified between two Gn/Gp SGSNs,

which is provided by the MME, and

- Gp functionality as specified between Gn/Gp SGSN and

Gn/Gp GGSN that is provided by the P-GW.

All this Gp and Gn functionality bases on GTP version 1 only. SGi Gp Gn S1-MME PCRF Gx S6a HSS S10 UE GERAN UTRAN Gn/Gp SGSN E-UTRAN MME S11 S8 SGW PGW Rx Gr vPLMN hPLMN S1u Operator's IP Services ( e.g. IMS, PSS etc.)

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Key concepts in mapping between

EPS and pre-Rel-8 QoS parameters

N/A N/A N/A Background 9 N/A No 3 Interactive 8 N/A No 2 Interactive 6 N/A No 1 Interactive 7 N/A Yes 1 Interactive 5 Unknown N/A N/A Streaming 3 Speech N/A N/A Streaming FFS Unknown N/A N/A Conversational 2 Speech N/A N/A Conversational 1 Source Statistics Descriptor Signalling Indication Traffic Handling Priority Traffic Class QCI

•There is a one-to-one mapping between an EPS bearer and a PDP context.

•The EPS bearer parameters ARP is mapped one-to-one to/from the pre-Rel-8 bearer parameter ARP.

•The EPS bearer parameters GBR and MBR of a GBR EPS bearer are mapped one-to-one to/from the pre-Rel-8 bearer parameters GBR and MBR of a PDP context

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TS 23.402

Architecture enhancements for

non-3GPP accesses

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TS 23.402 : Architecture enhancements

for non-3GPP accesses

The specification defines an architecture based on IETF

based protocols for

eUTRAN (LTE) access

Non-3GPP accesses such as WLAN, WIMAX, 3GPP2

The architecture using IETF based mobility procotol for

euTRAN better suited for operators with legacy non-3GPP

accesses that are transitioning over to 3GPP

Besides dealing with some specific inter-working issues for

3GPP2 systems, the specification provides multiple ways

for legacy 3GPP and LTE accesses to inter-work with

non-3GPP accesses which can in general be classified into

client based mobility mechanisms and network based mobility mechanisms

Although this allows flexibility but this also makes the

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Mobility Management Selection

No Mobility Mode or protocol is currently mandated for

inter-working with non-3GPP accesses

Static Configuration

For networks deploying a single IP mobility management

mechanism, the statically configured mobility mechanism can be access type and/or roaming agreement specific. The information about the mechanism to be used in such scenario is expected to be provisioned into the terminal (or the UICC) and the network

Networks Supporting Multiple IP

IP MM protocol selection between Network Based Mobility (NBM)

and DSMIPv6

Decision on IP address preservation if NBM is selected Example uses of IPMS include

initial attach to a non-3GPP access, when the IP MM protocol

selection is performed to decide how to establish IP connectivity for the UE.

handover without optimization from a 3GPP access to a non-3GPP access, where the IP MM protocol selection is performed to decide how to establish IP connectivity for the UE over non-3GPP access.

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Terminology: Trusted and un trusted

non-3GPP accesses

No precise definition but it can be safely assumed that

Trusted non-3GPP accesses can be the one that is owned

and operated by the LTE HPLMN. An example of this can

be the inter-working of a LTE operator with its legacy

3GPP2 network.

Untrusted non-3GPP accesses can be the one that is not

owned and/or operated by the LTE HPLMN. An example of

this can be a 3

rd

_{party WLAN inter-working with an LTE}

HPLMN.

The trust relationship of a non-3GPP access network is

made known to the UE with one of the following options:

1)If the non-3GPP access supports 3GPP-based access

authentication, the UE discovers the trust relationship during the 3GPP-based access authentication.

2)The UE operates on the basis of pre-configured policy in the UE.

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Non-Roaming Architecture for

3GPP Accesses within EPS using

PMIP-based S5

SGi

PCRF

S7

S6a

HSS

Operator's IP

Services

(e.g. IMS, PSS

etc.)

S1-U

S1-MME

E-UTRAN

2G/3G

SGSN

_S4

S3

S5

PMIP

Rx+

PDN

Gateway

MME S11

S10

S7c

Serving

Gateway

3GPP Access

Gxc Gx

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Roaming Architecture for 3GPP

Accesses within EPS using

PMIP-based S8

Ref: TS 23.402 hPCRF S6a HSS PDN Gateway HPLMN VPLMN S8 vPCRF S1-U S1-MME E-UTRAN 2G/3G SGSN _S4 S3 MME S11 S10 Gxc S9 SGi Gx Operator's IP Services (e.g. IMS, PSS etc.) Rx 3GPP Access Serving Gateway

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Non-Roaming Architecture using S5,

S2a, S2b

S G i P C R F G x H S S S 2 b SW n O p e ra to r's IP S e rvic e s (e.g. IM S , P S S e tc .) SW m SW x U n tru s te d N o n -3 G P P IP A c ces s SW a H P LM N N on -3 G P P N etw o rk s S 6b R x P D N G a te w a y eP D G 3 G P P A A A S e rve r G xb S 2 a G xa T ru s te d N o n-3 G P P IP A c c es s S T a G xc S 5 S 6 a 3G P P A c ces s S e rving G atew a y U E SW u

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Non-Roaming Architecture using S5,

S2c

SGi PCRF Gx HSS SWn Operator's IP Services (e.g. IMS, PSS, etc.) SWm SWx Untrusted Non -3GPP IP Access SWa HPLMN Non-3GPP Networks S6b Rx PDN Gateway Trusted Non-3GPP IP Access STa S2c S2c

ePDG 3GPP AAA _Server

UE Gxa Gxb Gxc S5 S6a S2c 3GPP Access Serving Gateway Ref: TS 23.402

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Routed

Six possible roaming scenarios in

specifications

h P C R F H S S T r u s t e d N o n - 3 G P P I P A c c e s s P D N G a t e w a y H P L M N S W d N o n - 3 G P P N e t w o r k s V P L M N v P C R F 3 G P P A A A P r o x y S T a 3 G P P A A A S e r v e r S 2 a G x a S 9 S G i G x S 6 b O p e r a t o r 's I P S e r v ic e s ( e . g . I M S , P S S e t c . ) R x S W x S W n e P D G S W a U n t r u s te d N o n - 3 G P P I P A c c e s s S W m S 2 b G x b G x c S 8 S 6 a 3 G P P A c c e s s S e r v in g G a t e w a y

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Additional functionalities or variations

in architectural entities

-

Serving GW

1.

local non-3GPP anchor for the case of roaming when the

non-3GPP IP accesses connected to the VPLMN.

2.

Event reporting (change of RAT, etc.)

3.

Uplink bearer binding and verification with packet dropping.

4.

Mobile Access Gateway (MAG) DHCPv4 and DHCPv6

functions

5.

Handling of Router Solicitation and Router Advertisement

messages if PMIP based S5 and S8 is used

1.

PDN GW

1.

user plane anchor for mobility between 3GPP access and

non-3GPP access.

2.

LMA if PMIP-based S5 or S8 is used.

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Additional functionalities or

variations in architectural entities

because of PMIP

MME

1.

Support for HRPD

PCRF

Home PCRF

1.

Terminates the Gx reference point for roaming with home

routed traffic;

2.

Terminates the Gxa, Gxb or Gxc/S9 reference points as

appropriate for the IP-CAN type.

Visited PCRF

1.

Terminates the Gxa, Gxb or Gxc reference points as

appropriate for the IP-CAN type;

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Evolved Packet Data Gateway

(ePDG)

1. Functionality defined for the PDG in TS 23.234 for the allocation

of a remote IP address:

• An IP address local to the ePDG which can be used as CoA for S2c; • An IP address specific to a PDN when S2b is used;

2. Routing of packets from/to PDN GW (and from/to Serving GW if

it is used as local anchor in VPLMN) to/from UE;

3. De-capsulation/Encapsulation of packets for IPSec and PMIP

tunnels (the latter only if network based mobility (S2b) is used);

4. Mobile Access Gateway (MAG) if network based mobility (S2b) is

used;

5. Tunnel authentication and authorization (termination of IKEv2

signaling and relay via AAA messages);

6. Local mobility anchor within untrusted non-3GPP access

networks using MOBIKE (if needed);

7. Transport level packet marking in the uplink;

• Enforcement of QoS policies based on information received via AAA

infrastructure;

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PMIP (S5/S8) QoS and Policy

Aspects

eNB PDN GW

UE

Service Data Flows

UL Packet Filter UL-PF→RB-ID

Service Data Flows

DL Packet Filter DL-PF→S1-TE-ID

RB-ID↔S1-TE-ID

Radio Bearer S1 Bearer

Application / Service Layer

IP Transport Leg Serving GW

DL Packet Filter DL-PF→TNL QoS

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PMIP-GTP roaming using direct

peering

S e r v in g G W ( P M I P ) v P C R F G x c G T P – H P L M N P M I P – V P L M N P M I P G T P S 9 S e r v in g G W ( G T P ) T o w a r d s o th e r P M IP o p e r a to r s P D N G W ( G T P ) P C R F G x G T P T o w a r d s o t h e r P M I P o p e r a to r s G T P – V P L M N S e r v in g G W ( G T P ) a ) P M IP V P L M N – G T P H P L M N b ) G T P V P L M N – P M I P H P L M N P D N G W ( P M I P ) h P C R F G x P M I P – H P L M N P M I P S 9 P D N G W ( G T P ) G x Ref: TS 23.402

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PMIP-GTP roaming using direct

peering with local breakout

Serving GW (PMIP) Serving GW (PMIP, GTP) PDN GW (PMIP) vPCRF PMIP hPCRF Gx S9 PMIP – VPLMN GTP – HPLMN Gxc Serving GW (GTP) Serving GW (GTP) PDN GW (GTP) vPCRF GTP hPCRF Gx S9 GTP – VPLMN PMIP – HPLMN

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PMIP-GTP roaming using

inter-working proxy

Serving GW PCRF Gxc GTP - HPLMN PMIP - VPLMN S8 PMIP S8 GTP S9 Interworking Proxy PDN GW PCRF Gx Protocol converter a) GTP HPLMN - PMIP VPLMN Protocol converter

GTP - VPLMN Interworking Proxy PMIP - HPLMN

b) PMIP HPLMN - GTP VPLMN Serving GW S8 GTP S8 PMIP S9 PDN GW PCRF Gx Ref: TS 23.402

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Network discovery and selection

UE

ANDSF

S14

3GPP IP Access or

Trusted/Untrusted

Non-3GPP IP

Access

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Non-3GPP Identities

NAI RFC 4282 based user identification defined in

TS 23.003 shall be used.

The username part of NAI shall be based on IMSI. This

applies to S2a, S2b and S2c reference points.

User identification in non-3GPP accesses may require

additional identities that are out of the scope of 3GPP.

These user identities, if not compliant to TS 23.003 are

however not sufficient to identify a user in the 3GPP

Evolved Packet Core.

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WiMAX inter-working

In Release, 8 WiMAX support is based on the

following principles

The EPS shall support mechanisms for delivery of

inter-system mobility, network discovery and

selection policies over the Sx interface.

The policies shall contain information e.g. on

availability of WiMax access networks that control the

UE selection of available WiMax access network and

the UE decision and triggering of 3GPP - WiMax

handovers

The handover procedure will be executed according

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CDMA inter-working

PDN GW S1-MME S10 MME S11 UE E-UTRAN S7 SGi S1-PCRF Operator's IP services Rx + S2a S101 HRPD AN PDSN IOS Serving GW S5 Sx-U Ref: TS 23.402

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3GPP Releases and SAE Features

Current plan is to

Meet the completion deadline of December 2008 by including only the SAE essentials and a shortened list of non-essentials in Release 8

Aim for a Short Release 9 (~1 year after release 8) to address remaining SAE features that could not be included in release 8

Aim for a Short Release 10 (~1 year after Release 9) for handling IMT/LTE Advanced features

List of Release 8 SAE Features

High level and common (for all accesses) functions (e.g. Roaming, QoS, etc…)

SAE for LTE - GTP variant SAE LTE - PMIP variant

Interoperation between LTE and 2G/3G LTE and CDMA2000

Single Radio Voice Call Continuity (SRVCC) Circuit Switched Fall Back (CSFB)

List of expected Release 9 SAE Features

SAE aspects of Emergency Calls

Functions and procedures for SAE to support LTE MBMS

Functions and procedures for SAE to support Control Plane LCS CS over EPS

Single Radio Aspects of SAE for Optimised Handover with WiMAX Home Node B

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Backup

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Reference Points

S1-MME: Reference point for the control plane protocol between E-UTRAN and MME. S1-U: Reference point between E-UTRAN and Serving GW for the per bearer user plane

tunnelling and inter eNodeB path switching during handover.

S3: It enables user and bearer information exchange for inter 3GPP access network mobility in

idle and/or active state.

S4:It provides related control and mobility support between GPRS Core and the 3GPP Anchor

function of Serving GW. In addition, if Direct Tunnel is not established, it provides the user plane tunnelling.

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.

S6a: It enables transfer of subscription and authentication data for authenticating/authorizing

user access to the evolved system (AAA interface) between MME and HSS.

Gx: It provides transfer of (QoS) policy and charging rules from PCRF to Policy and Charging

Enforcement Function (PCEF) in the PDN GW.

S8: Inter-PLMN reference point providing user and control plane between the Serving GW in the

VPLMN and the PDN GW in the HPLMN. S8 is the inter PLMN variant of S5.

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.

S10: Reference point between MMEs for MME relocation and MME to MME information transfer. S11: Reference point between MME and Serving GW.

S12: Reference point between UTRAN and Serving GW for user plane tunneling when Direct

Tunnel is established. It is based on the Iu-u/Gn-u reference point using the GTP-U protocol as defined between SGSN and UTRAN or respectively between SGSN and GGSN. Usage of S12 is an operator configuration option.

S13: It enables UE identity check procedure between MME and EIR.

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.

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Protocol assumptions

The S1-U is based on GTP-U protocol

The S3 is based on GTP protocol

The S4 is based on GTP protocol

The S5 is based on GTP protocol. PMIP variant

of S5 is described in TS 23.402

The S8 is based on GTP protocol. PMIP variant

of S8 is described in TS 23.402

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Key interfaces for inter-working

with non 3GPP accesses

S2a It provides the user plane with related control and mobility support between trusted non 3GPP IP access and the Gateway.

S2b It provides the user plane with related control and mobility support between ePDG and the Gateway.

S2c It provides the user plane with related control and mobility support between UE and the Gateway.

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

Gxb This interface is not specified within this release of the specification. Gxc It provides transfer of (QoS) policy information from PCRF to the

Serving Gateway

Note: names of some of the interfaces are currently being changed in the specification