Evolved EPC for LTE by Cisco

BRKSPG-2022

Evolved Packet Core for LTE Networks

Follow us on Twitter for real time updates of the event:

@ciscoliveeurope, #CLEUR

© 2012 Cisco and/or its affiliates. All rights reserved. Cisco Public BRKSPG-2022 2

Housekeeping

We value your feedback- don't forget to complete your online session evaluations after each session & the Overall Conference Evaluation which will be available online from Thursday

Visit the World of Solutions and Meet the Engineer

Visit the Cisco Store to purchase your recommended readings

Please switch off your mobile phones

After the event don’t forget to visit Cisco Live Virtual: www.ciscolivevirtual.com

Follow us on Twitter for real time updates of the event: @ciscoliveeurope, #CLEUR

http://www.ciscolivevirtual.com/

http://www.ciscolivevirtual.com/


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

Delivering voice with LTE/EPC

Agenda Evolved Packet Core

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….


… data was circuit switched

One burst 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


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


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.


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


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


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


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


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

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)


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


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


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


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


Destination

Network

LTE/EPC Key Components

Next

Generation

Cell Site

Mobility

Control

Node

PDN

interconnect

Mobility

Anchor


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


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

Ro Ga

LI

ADMF/DF

X1,x2,x3


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


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


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


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


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


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

LTE/EPC Interfaces and Basic Procedures


PCRF HSS

Gx

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

LTE Initial Attach

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)


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


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


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


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


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


EPS Security

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

USIM required for LTE

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


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


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


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


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


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


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


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


PMIP tunnel (no QoS)

Policy Control

GTP S5 Gx for enforcement in the PGW - PCEF (Policy and Charging Enforcement) in the PGW

PMIP S5 Gxc for enforcement in the SGW - No QoS information in PMIP

PGW

PCRF

TS 29.212

SGW UE

AF

S5

Gxc

Gx

Rx Event &

Access

Info

QoS

rules

Rules

Event &

Access

Info

Notifications

session

request

eNB

EPS bearer with PMIP S5

EPS bearer with GTP S5 On-path PCC

Off-path PCC

TS 29.214

Voice over LTE Strategies


Voice & SMS Services Providing Legacy Services in an LTE Network

The EPS architecture (3GPP Rel 8) is the first 3GPP all-IP architecture

Voice and SMS are still the cash cows for mobile operators

• Migration is critical

• User experience must be preserved

CSFB is the interim solution recommended by NGMN

IMS is the target solution for Telephony and Multimedia Services

OneVoice IMS profile ‘simplifies’ implementation for VoLTE

NGMN and OneVoice initiatives reduce risk of industry fragmentation

SMS typically required before voice due to EU regulatory requirements for data roaming services


Circuit Switched Fallback (23.272) 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


Circuit Switched Fallback (23.272) 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


Voice over IMS Mobile Origination

ISC

Mw

S1-MME

Sv

S11

Mg

SGi

(Gm from UE)

S6a

IuCS / A

IuPS / Gb

S3

S1-U

Cx

IMS (HPLMN)

To enable mid-call mobility, S-CSCF anchors call at SCC AS

TAS provides end-user services (e.g. IR.92)

MGCF provides breakout to PSTN or other CS networks

P-CSCF

SR-VCC UE E-UTRAN Serving/

PDN GW

MME

UTRAN /

GERAN

MSC Server

(SR-VCC)

SGSN

(SR-VCC)

I/S-CSCF

HSS

TAS SCC AS IP-SM-GW

MGCF

Subscriber has already registered

into IMS following EPC attach

UE Originates

Call

1

2


Voice over IMS UE roams during active call – SR-VCC mobility

ISC

Mw

S1-MME

Sv

S11

Mg

SGi

(Gm from UE)

S6a

IuCS / A

IuPS / Gb

S3

S1-U

Cx

IMS (HPLMN)

SCC AS performs leg management – hides mobility events from other IMS application servers

SR-VCC only works in one direction – LTE -> 2G/3G

Requires upgrades on legacy MSC infrastructure

P-CSCF

SR-VCC UE E-UTRAN Serving/

PDN GW

MME

SR-VCC UE UTRAN /

GERAN

MSC Server

(SR-VCC)

SGSN

(SR-VCC)

I/S-CSCF

HSS

TAS SCC AS IP-SM-GW

MGCF

UE retunes to 2G/3G

RAT during active call

1

New call leg

established

2

SCC AS performs

bearer management

and tears down original

leg

3


CSFB – Deployment Challenges

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)


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 LA1 MSC/VLR1

TA3 LA2 MSC/VLR2 MME

TA LA MSC/VLR

TA1 LA1 MSC/VLR1

TA2 LA1 MSC/VLR1

TA3 LA2 MSC/VLR2

Mapping Error Area


Roaming Retry TS 23.272/23.018

The Roaming Retry (complex) procedure is applied for mobile terminated calls where the MSC, to which the UE sends the LAU, is different from the MSC that sent the paging message to the UE.

MME

GMSC

VMSC

VMSC

1. IAM 4. IAM

5. SGs Page

6. Page

7. Location Update

HLR

2. SRI

3. PRN

8. UL

MME

GMSC

VMSC

VMSC

10. RCH (Resume Call Handling)

13. Call Establishment

HLR

11. SRI

9. Cancel Location

12. PRN

12. IAM

Scenario Leading to Roaming Retry Requirement

Roaming Retry Invocation


TA to LA Mapping Implementation Challenges

Most network operates deploying LTE already have both 2G and 3G networks

Mapping process has to take into account

When UE falling back, is it likely to go to 2G or 3G overlapping cells?

Where cell boundaries between 4G and 2G (or 3G) do not perfectly align, which is provisioned?

As cells ‘breathe’, boundaries become less predictable

4G networks will be growing rapidly in near-term – requires constant ‘tweaking’ of provisioning tables

4G TA’s

3G LA’s

2G LA’s

?

One major tier-1 EMEA operator has already concluded that it is not difficult to maintain accurate TA to LA mappings... ...it is, in their view, impossible

Therefore, Roaming Retry invocation will be more common than expected even though considerable effort may be expended maintaining tables


Dependencies for CSFB As Specified by TS 23.272

UE

UE must support CSFB procedures as defined with TS 23.272

MME

Must support SGs interface

Must support MSC/VLR selection procedures

MSC

Must support SGs interface (legacy MSC’s will require addition of IP interface cards)

Should support Roaming Retry procedure to minimise call drops

HLR

Should support Roaming Retry procedure to minimise call drops


Cisco CSFB Product Strategy

Cisco has developed a CSFB product strategy that addresses:

Inefficient operational deployment model – operators not forced to upgrade legacy MSC and HLR platforms

Investment legacy Capex spend – no investment required on legacy MSC or HLRs

Complicated MME provisioning procedure – requires only static TA-LA mappings

The Cisco solution places no dependencies on existing network elements (CS or EPC)

Supports both SMS (originate/terminate) and Voice (CSFB)

Roaming Retry procedural support not required


CSFB IWF – Architectural Fit

CSFB IWF

MSC/VLR

MMESGs

E-UTRANS1-MME

GERAN/

UTRAN

A/Iu

UE

LTE-Uu

Um

HSS

S6a

HLR

MAP

MAP

SMSC

MAP

CSFB IWF supports only SGs and MAP interfaces

Appears as a ‘thin’ MSC/VLR – is allocated a pseudo LA

Does not touch the bearer traffic within legacy network


EPC Attach / Location Update Procedure

1. UE Registers in LTE

2. Serving MME registers with HSS

3. Serving MME informs registered VLR

(CSFB IWF)

4. CSFB IWF registers as serving MSC with

HLR

HLR

MME

3G Core

4G Core HSS

MSC

RNC

3G Access

4G Access

CSFB IWF

4

3

2

1

MAP

SGs

4G UE

E-UTRAN

3G/4G Device


Mobile Originated SMS

1. UE initiates SMS

2. MME sends SMS to serving MSC (CSFB

IWF)

3. CSFB IWF sends SMS to SMSC › CSFB IWF performs SMS MO service logic › CSFB IWF performs SMS MO billing › CSFB IWF performs LI if required

HLR

MME

3G Core

4G Core HSS

MSC

BSC/RNC

3G Access

4G Access

CSFB IWF

3

2

MAP

SGs

SMSC

4G UE

E-UTRAN

3G/4G Device

1


Mobile Termination SMS

1. Incoming SMS to SMSC

2. SMSC queries HLR to determine routing

3. SMSC sends SMS to serving MSC (CSFB

IWF)

4. CSFB IWF sends SMS to MME › CSFB IWF performs SMS MT service logic › CSFB IWF performs SMS MT billing › CSFB IWF performs LI if required

5. MME sends SMS to UE

HLR

MME

3G Core

4G Core HSS

MSC

RNC

3G Access

4G Access

CSFB IWF

3

2

MAP

SGs

SMSC

4

1

4G UE

E-UTRAN

3G/4G Device

5


Mobile Origination

1. UE leaves LTE and re-tunes to

GSM/UMTS

2. UE Location Updates on GSM/UMTS

3. HLR sends Cancel Subscriber to CSFB IWF

› CSFB IWF Removes subscriber from VLR

4. UE initiates call

HLR

MME

3G Core

4G Core HSS

MSC

RNC

3G Access

4G Access

CSFB IWF

4

2

1

3G Device

MAP

SGs

3

4G UE

E-UTRAN

3G/4G Device

Note: MO Procedure utilised for Call Originations,

USSD and also for SS modifications


Mobile Terminated Call Signalling times and delays example

MME

GMSC

IWF

VMSC

1. IAM

5. Page

HLR

2. MAP SRI

10. MAP PRN

Note: only key messages are shown for simplicity (e.g. not all acknowledgments are shown)

4. SGs Page T0+7ms

6. LU

7. MAP UL

8. MAP CL T0+2222ms

9. SRI T0+2767ms

12. SRI ACK T0+2869

13. MAP PRN Resp T0+2880ms

11. MAP PRN Resp

14. MAP SRI Ack

15. IAM

16. Page

3. MAP PRN T0

Inserts MSRN from VMSC into original PRN

Response This delay may vary depending on RAN

conditions

500 ms additional delay to avoid race conditions


Benefits of CSFB IWF

Solution enables deployment of SMS over SGs and CSFB through a centralised gateway

Does not require SGs software licensing (or IP hardware upgrades) on any network MSCs

Operators no longer locked in to a existing vendors (current MSC suppliers) for CSFB solution

Reduced operational rollout costs and complexity

Common platform for other Cisco CSP services – ensures investment protection moving forward into IMS

Requires no specific TA to LA mapping changes on MME (i.e. MME is provisioned as if it is connecting to standard SGs interface)

Does not require or utilize Roaming Retry

Signalling only solution, no bearer impact


VoLTE (IMS) – Deployment Challenges

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

Service parity/consistency

Network complexity

Back office (re)integration

Legacy network dependencies (SR-VCC)

Call routing and optimisation


Single Radio Voice Call Continuity

SR-VCC

Voice call anchored in IMS over PS (e.g. LTE) access

UE moves to area of CS access only

UE is capable of transmitting/receiving on only one of those access networks at a given time.

Mobility handled at two levels

Radio

S1, Sv and MAP-E signaling

Application

SIP / SDP

Requires Service Centralization and Continuity Application Server (SCC AS)

From SCC AS perspective, seen as a PS to CS access transfer


Additional Resources

- 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

http://www.3gpp.org/

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

Recommended Reading

Please visit the Cisco Store for suitable reading.


Please complete your Session Survey

Don't forget to complete your online session evaluations after each session.

Complete 4 session evaluations & the Overall Conference Evaluation

(available from Thursday) to receive your Cisco Live T-shirt

Surveys can be found on the Attendee Website at www.ciscolivelondon.com/onsite

which can also be accessed through the screens at the Communication Stations

Or use the Cisco Live Mobile App to complete the

surveys from your phone, download the app at

www.ciscolivelondon.com/connect/mobile/app.html

We value your feedback

http://m.cisco.com/mat/cleu12/

1. Scan the QR code

(Go to http://tinyurl.com/qrmelist for QR code reader

software, alternatively type in the access URL above)

2. Download the app or access the mobile site

3. Log in to complete and submit the evaluations

http://www.ciscolivelondon.com/onsite

http://www.ciscolivelondon.com/connect/mobile/app.html

http://tinyurl.com/qrmelist


Thank you.

Evolved EPC for LTE by Cisco

Documents

Transcript of Evolved EPC for LTE by Cisco