Evolved Packet Core for LTE Networksd2zmdbbm9feqrf.cloudfront.net/2013/eur/pdf/BRKSPG-2022.pdf ·...

© 2013 Cisco and/or its affiliates. All rights reserved. BRKSPG-2022 Cisco Public

Evolved Packet Core for LTE Networks Kevin Gorey, Consulting Systems Engineer, EMEA

BRKSPG-2022


Mobile Network Evolution - From 2G to 3G

LTE/EPC introduction

LTE/EPC Interfaces and Basic Procedures - LTE/EPC Architecture and Interfaces

- Basic call flows (attach, intra-LTE mobility)

- Bearers, PDN connections and QoS

- Security

- Interworking with 2G/3G

International Roaming

Delivering voice with LTE/EPC

Cisco EPC Solution

Agenda Evolved Packet Core for LTE Networks

3


From 2G to 3G R8 Improving the mobile data services


Voice oriented architecture

Re-define fixed wireline services (e.g. SS and IN)

SMS is a signalling transport rather than a data service

Network transport based on TDM

There was wireless ISDN (aka GSM)

Base Station

Controller

(BSC)

Mobile Switching Center +

Visitor Location Register

(MSC/VLR)

Base Transceiver

System (BTS)

Mobile

Station

Home Location

Register (HLR) Service Control

Point (SCP) In the beginning….

5


… data was circuit switched

One burst of every TDMA frame was sufficient to transport a speech frame with source rate of 13 kbit/s

GSM Phase 2 (circa 1996) added Circuit Switched Data support offering 9.6 kbit/s service

High Speed CSD consisted in aggregating multiple timeslot for a single user but resource intensive

BSC MSC

Modem Interworking Function (IWF)

Modified V.110

3.1 kHz audio

or

V110 64k UDI

6


BSC MSC/VLR Gateway MSC

BTS

.. and eventually packet data with General Packet Radio System was bolted on

GSM Radio GSM Radio 64 kbps 64 kbps L1bis

MAC

IP

RLC

LLC

SNDCP

Relay MAC

RLC

Nw Services

BSSGP

Relay

L1bis

Nw Services

BSSGP

LLC

SNDCP

L1

L2

IP

UDP

GTP

Relay

L1

L2

IP

UDP

GTP

IP

Packet Control

Unit (PCU) Serving GPRS

Support Node

(SGSN)

Gateway GPRS

Support Node

(GGSN)

IP

7


Typical GPRS Packet Performances

Round Trip Times 700ms and 1000ms

Packet transfer interruption times between 2 and 8 seconds following a cell reselection and between 8s and 20s when the cell reselection triggers a routing area update

Application throughput up to 40 kbps using a handset capable of receiving 4 timeslots

Unable to reliably transport real time IP traffic

8


BSC SGSN GGSN

GRX

Visited PLMN Home PLMN

BTS

Home Based GGSN Roaming

GPRS Roaming Exchange (GRX)

GRX Services (as per GSMA IR.34)

DNS routing (for APN translation)

IP transport including routing & QoS

Security

In future release, GRX is enhanced to become IPX (IP exchange) and supports application proxy capabilities (e.g. for SIP), charging, etc.

9


3GPP UMTS System

First step towards an all IP network

New radio designed to accommodate greater packet throughput (up to 2Mbits/s initially… In reality, can support up to 384 kbit/s)

Core network remains largely unchanged from 2.5G

Migration to ATM for Radio Access Transport

More control into the RNC

3G RNC

3G MSC

3G SGSN GGSN

IP

ATM/AAL2

ATM/AAL5

Node B

PSTN

10


3G Packet Architecture

Radio Network

Controller (RNC) 3G SGSN GGSN

Iu-ps Gn/Gp

WCDMA

Radio

WCDMA

Radio ATM

MAC

IP

RLC

PDCP

Frame

Protocol

AAL2

ATM

AAL2

MAC

RLC

PDCP

ATM

AAL5

IP

UDP

GTP-U

IP

UDP

GTP-U

IP

UDP

GTP-U

ATM

AAL5

L1

L2

IP

UDP

GTP-U

L1

L2

IP

NodeB

11


Still Voice over CS bearer on the radio access, data bearer not suitable (latency, overhead)

Option to transport Voice over IP in the Core (see TS 23.205)

Introduction of SS7oIP transport

3GPP R4 Voice Services

Iu-cs

IP

MGW MGW

MSC-s MSC-s

HLR

ATM

Iu-UP

L1/2

IP AAL2

UDP

RTP

L1/2

IP

M3UA

TCAP

INA

P

MA

P

SCTP

SCCP

BIC

C o

r S

IP-T

H.2

48

Nb-UP

12


L1

RLC

PDCP

MAC

UDP

GTP-U

IP

3GPP R5 to R7: Addressing the Bottlenecks

Serving RNC 3G SGSN GGSN

Gn Iu-ps

IP

UDP

GTP-U

L1

L2

IP

IP

UDP

GTP-U

L1

L2

IP

UDP

GTP-U

L1

AAL5/ATM AAL5/ATM

L1

Frame

Protocol

AAL2/ATM

RLC

PDCP

WCDMA

IP

MAC

L1

Frame

Protocol

AAL2/ATM

WCDMA

Drift RNC

L1

FP

L1

FP

AAL2 AAL2

Node B

HSDPA Removes Drift RNC and

adds intelligence to the Node B

Direct Tunnel allows

SGSN to remove itself

from data plane

HSPA+: Distribute RNC

Data plane to Node B

MAC-HS MAC-HS L2

13


3G architrecture summary

Highlighting the growing importance of IP transport

3G MSC-S

3G SGSN GGSN

Core IP

IP RAN

w/ ATM PW

or Native IP

Node B

PSTN

3G RNC

3G MGW

HLR/HSS

SGW

14


Introducing LTE The 3GPP All-IP architecture


What is the LTE/SAE?

Evolved Packet System (EPS) is the technology direction for 3GPP based networks

Long Term Evolution (LTE) is the next generation 3GPP radio access network

- Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)

System Architecture Evolution (SAE) is the 3GPP next generation standard for mobile networks providing:

- Increased Bandwidth

- End-to-End IP

- Simplified Architecture

- Support for multiple radio access technologies

Evolved Packet Core (EPC) is the next generation 3GPP packet core

Consists of (3) main components (MME, SGW, and PGW)

16


3GPP Mobile Network Evolution

EPS = Evolved Packet System

GERAN

UTRAN

E-UTRAN

(LTE)

Non-3GPP

Access

Evolved

Packet Core

(EPC)

CS Network

LTE (Long Term Evolution) is the 3GPP WI that defined the E-UTRAN

SAE (System Architecture Evolution) is the 3GPP WI that defined the EPC

IP Services

/ Internet

17


The LTE Revolution

Radio Side (Evolved UTRAN - EUTRAN)

- Improvements in spectral efficiency, user throughput, latency

- Simplification of the radio network

- Efficient support of packet based services: Multicast, VoIP, etc.

Network Side (Evolved Packet Core - EPC)

- Improvement in latency, capacity, throughput, idle to active transitions

- Simplification of the core network

- Optimization for IP traffic and services

- Simplified support and handover to non-3GPP access technologies

18


LTE/EPC Key Attributes

Higher Bandwidth (>100 kbps per user on average) and improved latency

- Transmission and transition delays <10 & 100ms resp. in unloaded conditions

Service independent and data-only architecture

- Strict data QoS mechanism with no voice dedicated bearer identifictaion

Always-on model

- All registered users have a default bearer established used for signalling

IP addressing

- IPv6 by default with dual stack sessions (IPv4v6)

Support of alternative access technologies

- 3GPP and non-3GPP architecture, including possible wireline access

Local breakout

- Part of the traffic may be routed directly in the visited network

19


Destination

Network

LTE/EPC Key Components

Next

Generation

Cell Site

Mobility

Control

Node

PDN

interconnect

Mobility

Anchor

20


Evolved Packet System Architecture

GGSN RNC SGSN

NodeB

RNC

PGW

MME

eNodeB

SGW

PDN/

Internet

PDN/

Internet

From hierarchical architecture to flat IP topology

Open to centralized or distributed deployments

RNC functions distributed between the eNB and the EPC

21


UMTS, LTE/SAE Architecture:

Comparison

SGSN MME + Serving GW

- In the LTE architecture the SGSN functionality is split into MME & Serving GW

MME = Control Plane of SGSN

Serving GW = Data Plane of SGSN

GGSN PDN GW

- The PDN GW has similar function as the GGSN

IP Anchor

Policy Enforcement

Accounting/Charging

Deep Packet Inspection

22


UMTS, LTE/SAE Architecture:

Comparison

eNB

MME S-GW

P-GW

eNB

RNC

nodeB

SGSN

GGSN

nodeB

SGSN

GGSN

AAA HSS PCRF

UMTS UMTS

(Direct Tunnel) LTE-SAE

HSS/HLR

IuPs

Gn/Gp

Gi

Gi

Gx

Gr

S6a S6b

Gx

GTP-U

IuPs

S1-MME

S5/S8

S1-U

Gxc

SGi

Iub

S11

Gr

Gx

Iub

Gn/Gp

RNC

nodeB nodeB

Iub Iub

S10 Gn/Gp Gn/Gp

OCS CGF

Gy Ga

LI

ADMF/DF

X1,x2,x3

23


Key 3G <-> LTE terminology differences

3G

Primary PDP Context

Secondary PDP Context

Routing Area

P-TIMSI (Packet-

Temporary IMSI)

Attach

RAB Assignment

Request (Primary)

RAB Assignment

Request (Secondary)

LTE

Default Bearer

Dedicated Bearer

Tracking Area

GUTI (Globally Unique Temp ID)

includes GUMMEI)

Attach + Default Bearer Act

Initial Content Setup Request

Bearer Setup Request

24


EPC Protocol Stacks – Signalling Plane

UE

MME

S-GW

Evolved UTRAN (E-UTRAN) Evolved Packet Core (EPC)

HSS

PCRF

PDN-GW

MAC

RLC

PDCP

OFDMA

NAS

MAC

RLC

PDCP

OFDMA

L2

IP

L1

SCTP

S1-AP RRC RRC

L2

IP

L1

SCTP

S1-AP

NAS

S1-MME

36.413

S1-MME

eNodeB

25


EPC Protocol Stacks – Data Plane

UE

MME

S-GW


HSS

PCRF

PDN-GW

IP

L1

L2

IP (user)

IP

UDP

GTP-U

L1

L2 MAC

RLC

PDCP

OFDMA

IP (user)

MAC

RLC

PDCP

OFDMA

IP

UDP

GTP-U

L1

L2

IP

UDP

GTP-U

L1

L2

PMIP

S1-U S5/S8

S1-U

36.414 GRE GRE UDP

PMIP GTP-U S5/S8

29.274

(GTP)

-

29.275

(PMIPv6)

eNodeB

26


EPC Protocol Stacks – X2 interface

UE

MME

S-GW


HSS

PCRF

PDN-GW

X2

L2

IP

L1

SCTP

X2-AP

L2

IP

L1

SCTP

X2-AP

X2-C

L2

IP

L1

UDP

GTP-U

L2

IP

L1

UDP

GTP-U

X2-U

36.423 36.424

eNodeB

27


EPC Protocol Stacks – HSS & Policy

UE

eNodeB

MME

S-GW


HSS

PCRF

PDN-GW

Gx

L2

IP

L1

SCTP

DIAMETER

Gx

L2

IP

L1

SCTP

DIAMETER

L2

IP

L1

SCTP

DIAMETER

S6a

L2

IP

L1

SCTP

DIAMETER

29.272 29.212

S6a

28


GTP-U in 3GPP Architecture

RNC 3G SGSN GGSN

NodeB

RNC GGSN

NodeB

SGSN-S

SGW PGW eNodeB

1. 3GPP R6

2. 3GPP Direct Tunnel

3. 3GPP LTE/EPC

MME

29


EPC Roaming

Home Gateway Model

UE vS-GW

HSS PCRF

hPDN-GW

S8

MME

Visited Network

Home Network

S6a

Gx

eNodeB

Operator’s

IP Services

(e.g. video, IMS)

Rx

30


EPC Roaming

Visited Gateway Model aka Local Breakout

UE eNodeB vS-GW

HSS hPCRF

vPDN-GW

MME

Visited Network

Home Network

vPCRF

S9 S6a

Gx

Operator’s

IP Services

(e.g. video, IMS)

Rx

31


LTE/EPC Interfaces and Basic Procedures


PCRF HSS

Gx

LTE Initial Attach

eNodeB combines some RNC functionality with LTE radio MME (Mobility Management Entity) controls network selection, attach and

mobility - HSS for subscriber authentication

SGW (Serving GateWay) provides local mobility anchor, inter PLMN roaming, accounting

PGW (Packet Data Network GateWay) provides IP anchor, QoS and charging enforcement PCRF for PCC and QoS rules, service authorization

In case of PMIP access, the SGW interacts with PCRF and PGW with AAA

S5/S8 SGi S1-U

S1-MME

S11

S6a

LTE-Uu

PDN

DNS

UE selects PLMN and eNodeB and sets

up radio resources

eNB selects MME and sets up

connection if none established

previously

MME retrieves subscription information

and/or authenticates UE with HSS

DNS used to resolve APN and aid in

selecting PGW/SGW

MME sends Create Session Request to

SGW to set up default bearer

SGW forwards Create Session Request

to PGW to set up default bearer (GTP

S5 case)

PGW may retrieve PCC and QoS rules

for default bearer from PCRF

PGW assigns IP address(es) and binds

bearer to the PCC/QoS/billing rules

All elements (SGW, MME, eNB) are

updated and now traffic can flow

SGW PGW

eNB UE

MME

TS 23.401 Ch. 5.3.2.1 (for GTP S5)

or TS 23.402 Ch. 5.2 (for PMIP S5)

33


EPS Bearers

An EPS bearer uniquely identifies traffic flows that receive a common QoS treatment between a UE and a PDN GW (GTP) or SGW (PMIP)

Default bearer is assigned during attach and provides always‐on IP connectivity

- Internet‐like default connectivity for QoS‐agnostic needs (browser, email, etc.)

Dedicated bearer is assigned only when needed to provide guaranteed bit rate QoS control

- Assigned only for those QoS sensitive applications that can be recognized

PGW SGW UE S5

eNB

Default Bearer: network initiated during the Attach

PDN/

Internet

Dedicated Bearer: network initiated when needed

S1 SGi

1 PDN Connection

Example for S5 GTP

34


Multiple PDNs Connectivity

Each PDN connection has one default bearer - possibly one or more dedicated bearers

All bearers of the same PDN Connection use the same IP address(es) - IPv4, IPv6, or IPv4v6 (dual-stack)

Multiple PDN connections may be served by one or more PGW nodes - The UE can be attached to a single SGW at any point in time

Corporate

Network

Internet

IMS

PGW

SGW UE eNB

PGW

APN “corp.com”

PDN Type IPv4

APN “internet”

PDN Type IPv4v6

APN “IMS”

PDN Type IPv6

Default Bearer

Dedicated Bearer

35


Dedicated Bearer Activation

The PGW may activate a dedicated bearer, possibly after indications from UE or PCRF

The UE can only ask for the amount of resources, the network decides whether an existing bearer is modified or a new one is established.

3. Create Bearer Request

MME Serving GW PDN GW PCRF

4. Bearer Setup Request/ Session Management Request

5. RRC Connection Reconfiguration

2. Create Bearer Request

6. RRC Connection Reconfiguration Complete

7. Bearer Setup Response

10. Create Bearer Response

eNodeB UE

(A)

(B)

1. IP-CAN Session Modification

12. IP-CAN Session Modification

11. Create Bearer Response

8. Direct Transfer 9. Session Management Response

36


Setting up additional PDN connection

The UE initate the request indicating the APN for the PDN connection

Multiple APNs/PDNs must be managed by the UE and the applications

PDN Connectivity Request (APN,…)

UE MME S/PGW

Create Session Request

Create Session REsponse Bearer Setup Req. (def bearer)

eNB

RRC Bearer Setup Resp

PDN Connectivity Accept

PDN Connectivity Complete Modify Bearer

37


Quality of Service in the EPS

• QoS parameters per EPS‐bearer

- QoS Class Identifier (QCI)

Scalar value used for scheduling/RRM decisions

- Allocation and Retention Priority (ARP)

Used to accept/modify/drop bearers in case of resource limitation

- Guaranteed Bit Rate (GBR) and Maximum Bit Rate (MBR) only for dedicated bearers

• QoS paramers per group of EPS‐bearers

- Aggregate Maximum Bit Rate (AMBR)

Only for non‐GBR bearers, APN-AMBR and UE-AMBR

• Static mapping to/from 3GPP QoS partially standardized

- QCI ranges Traffic Classes

TS 23.401 Annex E

38


EPS Security

USIM required for LTE

Different set of keys used for ciphering, derived from the same original K stored in the USIM/HSS

E- UTRAN

MME

eNB

UE

HSS S6a

(Auth Vectors)

EPS AKA via S6a

Challenge and keys exchange

Mutual Authentication

NAS Integrity/Ciphering RRC Integrity and ciphering

U-Plane Ciphering

39


EPS Security

Multiple Keys derived from KASME

Integrity and ciphering on Radio and NAS

No integrity/ciphering on S1!

IPsec can be used to secure the backhaul

- Network Domain Security (NDS)

eNB

UE

RRC Integrity & ciphering

U-Plane Ciphering

SGW

MME

Unprotected!

NAS Integrity & ciphering

40


LTE Mobility Management

EPS Mobility Management (EMM) defines the relation between UE and MME resulting from mobility

EPS Connectivity Management (ECM) is related to the signaling connection between UE and MME

RRC state is related to the connection established between UE and E‐UTRAN

ECM-IDLE

EMM-DEREGISTERED

UE position unknown

No Context allocated

Signaling connection

establishment

Signaling connection

release

Attach

Detach

EMM-REGISTERED

ECM-CONNECTED

RRC_IDLE RRC_CONNECTED

ECM-IDLE

RRC_IDLE

UE position known at eNB level

Network controlled HO

Power

On

IP address(es)

allocated to the UE

UE position known at TA level

Cell reselection, paging

41


EPS Connectivity

UE and E‐UTRAN enter RRC‐CONNECTED state when the signaling connection is established between UE and E‐UTRAN

UE and MME enter ECM‐CONNECTED state when the signaling connection is established between UE and MME

Discontinuous Reception/Transmission (DRX/DTX) on the radio can influence the time the UE is in Connected/Idle mode

- E.g. maintain the UE in Connected mode with DRX cycle as long as the paging interval to save battery when the user is not transferring data

MME eNB UE RRC Connection S1 Connection

ECM Connection

TS 36.331 TS 36.413

42


TAI list 1

Short TA List: more TAU, less Paging

Long TA list: less TAU, more Paging

Tracking Area Update vs. Paging

MME

Enter Idle

Mode

Paging

Paging

Paging

Paging Paging

Paging

Incoming data

Enter

Connected

Mode

TAI list 2

43


TAU Procedure

The TAU may require a relocation of the MME (as in the picture) and/or also of the SGW

The new MME identifies the old MME from the MME Id included in the GUTI (Global Unique Temp. Id) sent in the Request

eNB eNB

Old MME

TAI not in

TAI list

Context Resp

Context

Request.

No UE context

availablle

TAU Request

HSS

NewMME

TAI list 2 TAI list 1 TAU Accept

44


X2 Based Handover

Data forwarding over X2 interface only during the handover

Fully eNB controlled, the EPC network is notified at the end

Better performance than S1 based handover, but requires additional connectivity in the RAN

eNB eNB

MME SGW

Measurement

Reports

HO Request

HO Request Ack.

HO Command Data forwarding

HO

Confirm

Path Switch Req.

Update Bearer

45


MME Pooling

Load Balancing: the MME sends a weight factor (RMC) to be used by the eNB for MME selection

Load re-balancing: procedures for node offload (O&M operation)

MME relocation required for load re-balancing or for mobility across different MME pool areas

UE

eNB eNB eNB eNB eNB

E-UTRAN MME Pool: area served by

one or more MME within

which a UE may be served

without need to change the

serving MME.

MME-1

RMC=1

MME-3

RMC=3

MME-2

RMC=2

RMC = Relative MME Capacity

46


EPC Node Selection

Process of Discovering/Choosing PGW, SGW, MME: - Initial Attach (PGW and SGW)

- Additional PDN Connection (PGW)

- Relocation/Handover (SGW, MME)

The MME shall select: - a PGW that provides the connectivity for a given APN

- a SGW to serve UE’s location

- a new MME to serve the target location (in case of relocation)

Dynamic discovery via DNS NAPTR - APN-FQDN for PGW

internet.apn.epc.mnc123.mcc456.3gppnetwork.org

- TAI-FQDN for SGW and MME

tac-lb12.tac-hb34.tac.epc.mnc123.mcc456.3gppnetwork.org

Selection based on multiple criteria - Co-location, static DNS indications

TS 23.003,

TS 29.003

TS 23.401

47


EPC interworking with Gn/Gp SGSN

Defined in 3GPP TS 23.401 Annex D

Based on legacy Pre-Rel-8 SGSN (Gn/Gp)

- Gn (GTPv1) interfaces on EPC (MME/PGW)

The PGW is the anchor point

- - The GGSN (Gn) function is integrated in the PGW

SGi

Gn

Gn

S1-MME

PCRF

Gx

S6a

HSS

S10

UE

GERAN

UTRAN

Gn/Gp

SGSN

E-UTRAN

MME

S11

S5

SGW PGW Operator 's IP Services (e.g. IMS, PSS etc.)

Rx

Gr

S1u

48


HLR/HSS Impacts

3GPP considers only the HSS from Release 8

- HLR functions expected to be integrated in the HSS

A combined HLR/HSS is required to maintain consistent information on network location, synchronizing the updates over S6a and Gr

Separated HLR and HSS should comunicate and have consistent provisioning (Security, services, ..)

E- UTRAN

UTRAN/ GERAN

MME

NB

eNB

SGSN

Gn (S3)

HLR HSS

Gr

S6a

RAU Example: MME to SGSN

49


EPC interworking with S4 SGSN

Defined in TS 23.401, Section 5.5.2

Based on a Release 8 SGSN, a.k.a. S4SGSN (Gn/Gp)

New interfaces between the SGSN and the MME/SGW

- GTPv2-C like in EPC

The S-GW is the anchor point for GERAN/UTRAN and E-UTRAN

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 S6d

50


International Roaming


PLMN

PS Core

VPLMN

PS Core

Voice calls routed in the VPLMN

- HPLMN Interaction limited to the HLR

- lower delays, optimized routing

GRX

VPLMN

CS Core

HPLMN

CS Core

Other

Network Voice call

Subscription

management

UE

Internet

UE

Data session

Different approach for voice (CS) and data (PS)

Data traffic home-routed

- Service control in the HPLMN

- Reduce delays

52


Roaming in All-IP 4G Networks

GRX

VPLMN

HPLMN

LTE/EPC and all-IP evolution brings new challenges

Continue to route Data Traffic to the

HPLMN?

Offload gaining momentum

Can the VPLMN provide the same

voice/SMS services like in the home

network?

Large consensus for voice technology is

required

53


3GPP Architecture for LTE Roaming

GTP or PMIP for S8

Diameter interfaces inter-PLMN: S6a, S6d, S9

Gp interworking with legacy SGSN possible on PGW (Annex D)

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

PDN Gateway

S 1 - U

S4

Home-Routed Local Break-Out

S6a

HSS

S 5

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

From 3GPP TS 23.401

54


GSMA and Roaming

GSMA continues to define inter-operator policies and infrastructure for roaming

IR33 defined GPRS roaming - Open Connectivity program to certify roaming hubs

IR.88 addresses interworking scenarios for LTE Roaming

IR.67 addresses inter-PLMN DNS - GPRS, EPC extensions, ENUM , etc.

Voice/SMS support brings new requirements and issues

- IR.92 VoLTE and extensions (IR.58 for HSPA, IR.94 for videocall)

- IR.65 IMS Roaming

55


EPC Roaming Scenario Multiple Entities, Different Requirements

PDNs

Transport

EPC

MME/SGSN SGW

PCRF

Services

CS Net

PGW

EPC

HSS

PCRF

PGW

Local

policy

IMS/CS roaming

DNS Diameter

IP/IPsec IP/IPsec

VPLMN GRX HPLMN

Author. & Policy

Node Selection

Diameter Routing

Security Transport

IP/IPsec

IMS

Services

CS Net IMS

RA

N

Roaming Sub

UE

DNS Diameter DNS Diameter

56


Diameter Edge Agent

New Edge node for Diameter traffic handling

Little DEA/DRA standardization, multiple possible tasks: - Diameter Proxy or Relay for multiple applications (S6a, S6d, S9)

- Node discovery (e.g. find the HSS in the HPLMN)

- Routing, scalability and availability

- Easy interoperability (e.g. AVP manipulation)

- Security, including network hiding and encryption

- Roaming Steering should be aligned with analogous SS7 mechanisms

From GSMA IR.88

No more SS7 inter-PLMN,

multiple Diameter interfaces

57


Diameter Peering

Multiple peers with associated weights can be set - Round robin across peers of equal weights

- Load balancing with clusters of different weights

Diameter peer tuning - Destination-host AVP or just Destination-Realm first message

- Timeouts and retries

MME HSS /EIR

lookup

DEA

Diameter Req. (Dest. Realm)

Diameter Req. (Dest. Server)

Diameter Resp. Diameter Resp.

Example of

Interworking with

DEA

58


SGW and PGW Selection for roamers

Multiple AVPs from the HSS can influence PGW selection - VPLMN-Dynamic Address-Allowed

- Operator Determined Barring (for VPLMN and/or HPLMN)

- APN-OI Replacement (optional indication from HSS)

- PDN-GW Address (no DNS discovery)

PMIP vs. GTP S8 in Service Parameter (DNS Discovery) - internet.apn.epc.mnc456.mcc… IN NAPTR 1 5 "a" "x-3gpp-pgw:x-s8-gtp" "“ nodes1.pgw.3gpp…

SGW Selection based on TAI as in normal Attach

Normal selection criteria and local SGW/PGW pools applicable as in non-roaming scenario in case of local PGW selection

59


Example of Home Routed Scenario DNS Discovery of SGW and PGW

GR

X

PLMN A (V-PLMN) PLMN B (H-PLMN) MCC= 123, MNC = 456

MME

UE

DNS

SGW

HSS

PGW

Attach Request (IMSI 123456xxxxxxxxx)

(VPLMN_ADDR_NOT_ALLOWED, HPLMN service not barred)

NAPTR internet.apn.epc.mnc456.mcc123.3gpp…

PGW_name x-3gpp-pgw:x-s8-gtp

Home routed MCC/MN

from IMSI

DNS resolving APN FQDN via authoritative DNS for HPLMN

SGW Discovery via TAI FQDN NAPTR selection criteria in the MME

S8

S6a

DNS

Create Session Request

Subscriber of PLMN B roaming

in PLMN A

Local DNS of PLMN A

GRX’s DNS is authoritative for other

domains

60


EPC for LTE and 2G/3G access

All operators have roaming agreements with other operators for GPRS/UMTS data service

LTE is not deployed everywhere at the same time

Mixed roaming agreements for 2G/3G/4G - 2G/3G-Only

- LTE-Only

- 2G/3G and LTE, with or without I-RAT

The HPLMN and the VPLMN may have different capabilities with regards to 2G/3G/4G support

- I-RAT support

- Combined EPC vs. Overlay

- Gn-SGSN vs. S4-SGSN

61


2G/3G Roaming via Gp in EPC

Gp enabled PGW, to interoperate with legacy SGSN

2G/3G roaming and LTE roaming in parallel - local policies and restriction may to be coordinated

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.)

From TS 23.401

Annex D

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Multiple Options with S4SGSN

S4SGSN deployment will happen gradually, legacy interfaces must be still supported

S6d or 3GPP-Rel-8 Gr required to enable EPS sessions over S4 - 3GPP Rel-7 Gr would work for PDP Context over Gn/Gp

Both Gn/Gp and S4 can be used towards the GGSN/PGW

HLR/HSS PGW/

GGSN

S4SGSN

HPLMN

VPLMN

MME

SGW

S8 Gp

Gr

S4

S3/Gn

S11 S6d or Gr?

Gp or

S4/S8?

S6d

63


Delivering voice with LTE/EPC


Why VoLTE? The Bigger Picture

2G/3G Voice

Equivalency

LTE Has no equivalence to circuit core

CSFB and VoLTE are alternatives for

providing voice to LTE attached UE’s

Optimised

Infrastructure

Future VoLTE network based on open

standards

Strong driver for migration beyond CSFB

is network convergence

Opportunity for collapse of network silos

Converged

Services

Access agnostic services

Implement once and deploy across

multiple access types

Innovative service combinations become

possible (e.g. Single pre-paid balance

across fixed/mobile)

Rich Services

Migration from CSFB to VoLTE enables

rich voice services to be delivered in

combination with capabilities such as

those enabled by RCSe/RCS

The investment should be seen in the context of the overall benefits and

not just ‘replicating voice’

VoLTE

65


Evolution of Voice Services From Legacy Voice to VoLTE

Circuit Switched Voice

and legacy SMS

services

• Still over 80% of operator revenues

• Cash cow – preservation critical

• User experience critical

2010 2013

Reference UE

availability

Limited Trials

(pre-IR.92 UE)

Commercial UE

availability

Trials

VoLTE – IR.92

SR-VCC

Deploy

2011

Circuit Switched

Fallback (CSFB)

Reference UE

availability

Trials

Commercial UE

availability

Deploy

• ‘Interim’ solution, however will remain in

network for roamers and 1st gen devices

• SMSoLTE critical for LTE roaming services

2012

66


Circuit Switched Fallback Delivery of SMS to EPC Attached Subscriber

S1-MME

SGs

S11

S6a

IuCS / A

S1-U

During EPC attach, CSFB UE’s are also attached over SGs to MSC

MME maintains mapping of TA to LA to determine appropriate MSC to establish SGs association with

SMS can be delivered/sent without FallBack to legacy radio (SGs interface includes SMS payload capability)

CSFB UE E-UTRAN Serving/

PDN GW

MME

UTRAN /

GERAN MSC

HSS

Incoming SMS 1

SMS is delivered via SGs interface 2

67


Circuit Switched Fallback Delivery of Terminating Voice Session to EPC Attached Subscriber

S1-MME

SGs

S11

S6a

IuCS / A

S1-U

SGs interface is used to inform UE of incoming call

SGs Paging triggers UE to retune to 2G or 3G legacy network

Page Response sent via the legacy radio network

Call terminates to UE ‘normally’

CSFB UE E-UTRAN Serving/

PDN GW

MME

CSFB UE UTRAN /

GERAN MSC

HSS

Incoming Call – delivered to VMSC which

has SGs association for this subscriber

1

UE is paged via the SGs interface 2

UE retunes to 2G/3G RAT on

receipt of page

3

UE Responds to paging –

incoming call terminated via

standard 2G/3G procedures

4

68


CSFB – Deployment Challenges

CSFB was initially seen as the ‘easy’ interim approach

As further analysis of CSFB was performed, the identified challenges mounted

Some of the major challenges/difficulties facing CSFB rollout are:

Legacy network dependencies

Continued legacy network spend/investment

Fallback latency / post-dial delay

Ongoing operational complexity (TA/LA mapping)

69


CSFB – MSC/VLR Selection As defined in 23.272

TA1 TA2 TA3

LA1 LA2

MSC/

VLR1

MSC/

VLR2

TA1 TA2 TA3

LA1 LA2

MME

MSC/

VLR1

MSC/

VLR2

TA LA MSC/VLR

TA1 LA1 MSC/VLR1

TA2 LA2 MSC/VLR2

TA3 LA2 MSC/VLR2 MME

TA LA MSC/VLR

TA1 LA1 MSC/VLR1

TA2 LA1 MSC/VLR1

TA3 LA2 MSC/VLR2

Mapping

Error Area

70


Single Radio Voice Call Continuity (SR-VCC)

VoLTE call begins using IMS Multimedia Telephony (MMTel) services

MMTel Telephony Application Server (TAS)

SR-VCC mobility steps:

Handover triggered by E-UTRAN, based on measurement reports

MME initiates handover signaling towards a MSC

MSC prepares GERAN/UTRAN for the call

SCC AS in IMS executes access transfer at the application layer

Call handed over from LTE to 2G/3G

PS session mobility handled separately

LTE coverage CS (2G/3G) coverage SR-VCC handover

71


Cisco EPC Solution


ASR5000 and ASR5500 Platform Purpose built for the mobile market

Cisco ASR5000 & ASR5500 Optimized for Throughput,

Transactions, and Density

Processing

Power

Bandwidth

ROUTER / SWITCH

Servers

Competitive platforms optimized for bandwidth

Competitive platforms optimized only for

transactions

73


GERAN

E-UTRAN eNodeB

UTRAN

BTS

NodeB

WiFi/Femto/Oth

er

WiFi / Femto /

Untrusted

Evolved Packet Core

Not a dedicated “LTE Radio” core

SGSN

HSGW

S1-MME

eHRPD

Access

eHRPD

MME SGW PGW 4G

3G

Non-3GPP

Evolved Packet Core

74


Seamless Flexible EPC Collapsing Functions

SGSN/ MME

PGW GGSN

SGW/PGW GGSN

Localization for end points served by the same GGSN/PGW, including VoIP, data

Walled garden services from a centralized, e.g., Mobile TV, Gaming, VoD

Local breakout for internet services lower network backhaul costs

Optimizes external interaction, minimizes inter-node inter-technology signaling, lowers latency

2.5G

4G

3G Operator’s IP

Service Domain

SIP/VoIP

Internet

75


3G to 4G Migration Upgradeability

Lack of upgradeability of 2G/3G HW to support 4G and Co-location issue = CAPEX

and OPEX and network impacts

NodeB NodeB

GERAN/ UTRAN

E-UTRAN

eNB

GERAN/ UTRAN

E-UTRAN eNB

Competition:

Forklift Upgrade

No Co-location possible

Cisco Advantage:

Integration activity only

2G/3G/4G//EPC Co-location

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- www.3gpp.org

- http://www.thespectool.com/v2/index.php

Relevant 3GPP Specifications:

• TS 36.300 E-UTRA and E-UTRAN Overall description; Stage 2

• TS 36.331 E-UTRA; Radio Resource Control (RRC); Protocol specification

TS 23.401 GPRS enhancements for E-UTRAN access (EPC)

TS 23.402 Architecture enhancements for non-3GPP access

• TS 24-301: Non-Access-Stratum (NAS) protocol for EPS; Stage 3

• TS 29.272: EPS; MME and SGSN related interfaces based on Diameter protocol

• TS 33.401 3GPP SAE; Security architecture

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http://www.3gpp.org/

http://www.thespectool.com/v2/index.php


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