epc architectured2zmdbbm9feqrf.cloudfront.net/2012/usa/pdf/brkspm-3515.pdf · epc architecture:...

© 2012 Cisco and/or its affiliates. All rights reserved. Presentation_ID Cisco Public

EPC Architecture: Optimized for IMS, Policy and VoLTE

Kevin Smith, CSE


Voice over LTE (VoLTE) IMS-based telephony service over LTE radio access

Long Term Evolution (LTE) • 3GPP defined for 4G radio access

• Evolved Universal Terrestrial Radio Access Network

• Evolved Packet Core

• 3GPP Defined packet core architecture

• Architecture supports “any” access with Policy

IP Multimedia Subsystem (IMS) • 3GPP defined architecture to delivery packet based telephony services

• Signaling domain replacing “Circuit Switch” technologies

• Supports “any” access

• “oneVoice” • GSMA Defined minimum requirements to support VoLTE (IR.92)

E-UTRAN IMS

eNodeB

EPC MME

SGW PGW

AS CSCF

Internet

“It is clear now – if there was ever any real doubt – that IMS is the preferred choice of mobile operators to support voice service in LTE networks”

Gabriel Brown / Heavy Reading (Jan 26, 2011)

PCRF

AS


4G/LTE Technology Evolution Impacts of migration from Circuit Switch to all IP

“Traditional” SS7-MAP interfaces replaced by SIP and Diameter • IMS uses SIP for call control

• PCC, IMS, EPC architectures use diameter for communication

• Roaming uses Diameter interfaces (S9, S6a, S6d)

• Diameter-MAP interworking required for certain roaming scenarios

VoLTE result in exponential growth in SIP and Diameter TPS • “Normal” PDN establishment or modification

• Gx – impacts PGW/PCRF

• Rx – impacts P-CSCF/PCRF

• Cx – impacts HSS/S-CSCF

• Gy - impacts PGW/OCS

• IMS flows increase DNS TPS load

IMS

PS CS

Internet

Access


“4G” Signaling Growth Solutions Diameter Interfaces and signaling transactions

HSS PCRF

CSCF OCS

MME

PCEF

P-CSCF

Gx, Gy

Rx

S6a Gx, Rx, S9

Gy

Cx/DX

SGSN

S6d

Signaling Paradigm Shift introduces operator challenges • Rebuilding mesh of signaling interfaces • Topology simplification • Scalability / Capacity issues • Congestion Control

EPC

Policy

IMS

Result in increased signaling

The DRA is a functional element that ensures that all Diameter sessions established over the Gx, S9, Gxx and Rx reference points or a certain IP-CAN session reach the same PCRF when

multiple and separately addressable PCRFs have been deployed in a Diameter realm.

This presentation will focus on “option 2”

Solution Options Option 1: DRA - Diameter Routing Agent

• Defined by 3GPP/GSMA to help address these challenges • Load Balancing, Protocol Interworking, Topology Hiding, etc DRA Definition (29.213):

Option 2: Architecturally • Intelligent approaches to reduce diameter signaling • Topology simplification for simplified VoLTE deployments

Policy, IMS and EPC Communication


3GPP Policy and Charging Controls Architecture

All “communication” from IMS (AF) domain to EPC domain (PCEF) flows through PCRF

Overall PCC architecture 3GPP 23.303

Gy

Gz

Subscription Profile

Repository (SPR)

Rx

AF Sp

Gx

Offline Charging System (OFCS) Gateway

PCEF

Policy and Charging Rules Function

(H-PCRF)

Gxx

BBERF

Policy and Charging Rules Function (V-PCRF)

S9 VPLMN

HPLMN

Online Charging System (OCS)

Gateway

Cisco Confidential © 2010 Cisco and/or its affiliates. All rights reserved. 8

Basic VoLTE Call Flow PGW/PCRF/P-CSCF communication

SIP Diameter

Rx

Network Gm

Gx

PCRF

P-CSCF PGW

E-UTRAN

PCRF

1

(1) P-CSCF receives SIP Answer message with SDP Payload (2) P-CSCF sends “SDP” info to PCRF (3) PCRF responds to P-CSCF (4) P-CSCF forwards SIP Message (5) PCRF sends notification to create or updates bearer credentials (6) PGW responds to PCRF (7) PGW updates bearer as requested by PCRF

2 3 5

6

7

4

SIP: Session Initiation Protocol SDP: Session Description Protocol PCRF: Policy and Charging Rules Function PGW: Packet Data Network Gateway P-CSCF: Proxy Call Session Control Function

The “called” user answers

Note: RFC 3312 “pre-auth” not shown


Diameter Messages Rx and Gx P-CSCF, PCRF, PGW Interaction

Internet

PCRFPCEF

CCR

CCA

Application Service (IP Flows)

RAR

RAA

P-CSCF

AAR

AAA

InternetApplication Service (IP Flows)

STR

STA

RAR

RAA

ASA

ASR

Gx Rx

Bearer traffic P-CSCF to PCRF interaction • Authorizing of the IP flows and the QoS resources for an IMS session.

Control Traffic P-CSCF to PCRF interaction P-CSCF subscribers to PCRF for traffic plane events

• Credit Control Request (CCR) • Credit Control Answer (CCA)

• Re-Authorization-Request (RAR) • Re-Authorization-Answer (RAA)

• Authorization Authentication Request (AAR) • Authorization Authentication Answer (AAA)

• Session Termination Request (STR) • Session Termination Accept (STA)

• Abort-Session-Request (ASR) • Abort-Session-Answer (ASA)

Diameter Messages


EPS Bearer Overview

Each Bearer has a QCI, ARP (GBR, MBR)

Internet APN Default Bearer

IMS APN Default Bearer

IMS APN Dedicated Bearer

Media-Flow-Description

QoS for the default bearer for PDN is part of subscription

profile stored in the HSS.

A default bearer is created when the UE creates a connection to the PDN which is used for IMS telephony with a standardized QCI value of 5 for IMS SIP signaling.

The network shall initiate the creation of a dedicated bearer to transport the voice media. The dedicated bearer for Conversational Voice shall utilize the standardized QCI value of 1.

AMBR Aggregate Maximum Bit Rate APN Access Point Name ARP Allocation/Retention Policy GBR Guaranteed Bit Rate

MBR Maximum Bit Rate QCI QoS Class Identifier RAT Radio Access Technology TFT Traffic Flow Template

All “communication” from IMS domain to EPC domain

flows through PCRF

Signaling Optimization – Step 1: Collapse Traffic Plane Event Communication - Reduce Rx/Gx transactions


Model 1 Model 2 Model 4 Model 3

Fully Distributed Intelligent Edge Fully Collapsed IMS-in-a-box

Flexible Packaging Options Operator Driven Configuration Models

• The ASR 5000 provides unrivalled packaging flexibility

• Platform capabilities enabled via software key on single software load

• Architectural flexibility as technologies and client capabilities change

• Ensures optimal configuration for small & large operators

• Ensures configurations can align with operators current topology

• Ability to seamlessly migrate from one model to another


EPC, IMS, and Policy Communication Integration Points: Gx (PGW/PCRF) & Rx (PCRF/P-CSCF)

Rx

Gx

OCS

UE

Gy

eNodeB

S11

Gi Packet Data

Network

P-CSCF

Subscriber DB Infrastructure

SPR

Services

Mw Provisioning

Billing

Step 1: Collapse P-CSCF and PGW (SAE-GW) • Optimize use of existing HW footprint • “Internalize” traffic-plane event communication • Enable IMS “IP-CAN” Awareness • Simplify routing and failover scenarios

SGW/PGW

P-CSCF

Mw

S1-MME

S1-U

MME

I/S-CSCF

PCRF

HSS

“local policy”

Step 2: Enhanced local policy • Well known IMS APN provides operator flexibility • “local policy” instead of PCRF to expedite deployment • Reduce network transactions • Reduce call setup time and network induced latency

Diameter

SIP

Cx


Traffic Plane Events P-CSCF/PCRF communication for PGW “bearer” events

Traffic Plane Events IP-CAN Session Termination

Service Data Flow Deactivation

Notification of Signalling Path Status

IP-CAN/RAT type change Notification

Access Network Charging Information Notification

Traffic plane events can be offloaded from the PCRF without

impacting standard call flow


Optimized Traffic Plane Event Communication Ex: Subscription to Notification of Signaling Path Status

PGW (PCEF)

NetworkP-CSCFPCRF

Gx: CCR-U Indication of loss of

signaling bearer

Rx: STA

Rx: STR

Bye

Gx: RARGx: RAA

200 OK

Gx: CCA-U

Configurable to deregister

Internal communication

RxGx

Collapsed P-CSCF/PGW PGW

(PCEF)NetworkP-CSCFPCRF


signaling bearerRx: RAR

Specific-Action AVP ="INDICATION_OF_LOSS_OF_ BEARER" deactivated IP Flows identified in Flows AVP

Rx: RAA

Rx: STA

Rx: STR

Bye

Gx: RARGx: RAA

200 OK

AARP-CSCF subscribes to notification this session

Specific-Action AVP=“INDICATION_OF_LOSS_OF BEARER”, Flow-Usage AVP="AF_SIGNALLING”

AAAGx:RAR “Event-trigger”

Gx:RAA

When not all the service data flows within the P-CSCF session are affected, the PCRF shall inform

the P-CSCF by sending an RAR command.

When all the service data flows within the P-CSCF session are affected, the PCRF shall inform

the P-CSCF by sending an ASR command

Rx: ASRRx: ASA

Gx: CCA-U


RxGx

Separate P-CSCF/PGW

Transaction savings

PGW (PCEF)

NetworkP-CSCFPCRF


signaling bearerRx: RAR

Specific-Action AVP ="INDICATION_OF_LOSS_OF_ BEARER" deactivated IP Flows identified in Flows AVP

Rx: RAA

Rx: STA

Rx: STR

Bye

Gx: RARGx: RAA

200 OK

AARP-CSCF subscribes to notification this session

Specific-Action AVP=“INDICATION_OF_LOSS_OF BEARER”, Flow-Usage AVP="AF_SIGNALLING”

AAAGx:RAR “Event-trigger”

Gx:RAA

When not all the service data flows within the P-CSCF session are affected, the PCRF shall inform

the P-CSCF by sending an RAR command.

When all the service data flows within the P-CSCF session are affected, the PCRF shall inform

the P-CSCF by sending an ASR command

Rx: ASRRx: ASA

Gx: CCA-U


RxGx

PGW (PCEF)

NetworkP-CSCFPCRF


signaling bearer

Rx: STA

Rx: STR

Bye

Gx: RARGx: RAA

200 OK

Gx: CCA-U


Internal communication

RxGx


Traffic Plane Events P-CSCF/PCRF communication for bearer plan events IP-CAN Session Termination

• 4 Rx transactions: PCRF sends P-CSCF ASR on each active Rx Diameter session. P-CSCF responds with ASA and a STR command to the PCRF. PCRF acknowledges with STA to P-CSCF

Service Data Flow Deactivation

• 2 Rx Transactions: PCRF sends RAR (specifying deactivated IP Flows) the P-CSCF responds with RAA (P-CSCF may send additional AAR to updae session info the PCRF, PCRF responds with AAA ).

• If all SDFs are affected, PCRF sends ASR and the P-CSCF responds with ASA . The P-CSCF will then sent STR and PCRF will respond with STA

Notification of Signalling Path Status

• 2 Rx Transactions: PCRF sends RAR to the P-CSCF and the P-CSCF responds with RAA to the PCRF.

• P-CSCF may optionally send STR and PCRF respond with STA

IP-CAN/RAT type change Notification

• 2 Rx transactions: PCRF sends RAR and the P-CSCF responds with RAA

• P-CSCF may optionally send STR and PCRF respond with STA

Access Network Charging Information Notification

• 2 Rx Transactions: PCRF sends RAR and the P-CSCF responds with RAA

Opportunity to significantly reduce Rx and Gx transactions


Collapsed Traffic Plane Events Communication Example Transaction Savings

Input parameterCalculated parameter

Operator Defined Call ModelTotal Number of Registered Subscribers 10,000,000Total Number of Registration / Deregistration per hour 10,000,000VoIP penetration (% of reg subs capable of VoIP call) 10%Avg Call Attempts per hour per VoIP Sub 1Avg total VoIP call attempts per hour 1,000,000 Call Duration (Min) 3% of Inter-Technology Handovers per hour 5%Avg Inter-technology handovers per hour 500,000

3GPP defined "Subscribed" to Traffic Plane Events

Minimum transactions

between PCRF/P-CSCF

Minimum transactions between PCRF/P-CSCF (Rx interface) per sub/hr

per event per traffic plane event based on above call model

Enabled(yes = internal P-CSCF/PGW

communication used instead of Rx interface to PCRF)

IP-CAN Session Termination 4 40,000,000 yesService Data Flow Deactivation 2 2,000,000 yesNotification of Signall ing Path Status*

2 20,000,000 yes

IP-CAN/RAT type change Notification * 2 1,000,000 yesAccess Network Charging Information Notification* 2 1,000,000 yesPre-Auth Savings (Rx trigger from SDP Offer not used)* 2 2,000,000 yesSDP Answer Trigger (required unless there is not PCRF) 2 2,000,000 noIMS Registration Procedures 2 10,000,000 no

Signaling Optimizationtotal messages (no offload) per hour 78,000,000 Total transaction savings per hour

(Rx transactions offloaded from PCRF and internalized in P-CSCF/PGW)66,000,000

% Diameter Msg Reduced from PCRF from P-CSCF (based on call model) 84.62%

*note: the above assumes on subsribed to events are requested in the origina l AAR/AAA exchange with the PCRF during IMS regis tration. If a separate AAA/AAR is required, this would increaes the tota l transaction load and the benefi t of col lapsed solutoin would be of greater va lue.


Signaling Optimization: Collapsed Traffic Plane Event Communication

Rx

Gx

UE

Gy

eNodeB

S11

Gi

Packet Data Network

SPR

Mw Provisioning

Billing

SGW/PGW

Cx

S1-MME

S1-U

MME

I/S-CSCF HSS

OCS PCRF

P-CSCF

Rx

Gx

UE

Gy

eNodeB

S11

Gi

Packet Data Network

P-CSCF

SPR

Mw Provisioning

Billing

SGW/PGW

Cx

S1-MME

S1-U

MME

I/S-CSCF

HSS

OCS PCRF DRA

DRA

Separate P-CSCF/PGW Architecture Collapsed P-CSCF/PGW Architecture

Optimized Architecture Benefits

• Significantly reduce/eliminate Gx/Rx transactions • Network Consistency Across IMS/EPC Domains • Reduce expenditure in peripheral node capacity • Efficient routing of emergency services • Minimize network induced latency • Reduce nodes results in Capex/Opex Savings

Optimized

Signaling Optimization – Step 2: Remove PCRF dependency for VoLTE calls


“One Voice” VoLTE Requirements

IR.92 requires dedicated “IMS APN” • The IMS application must use the IMS well known APN as defined in PRD IR.88;

IR.92 specifies bearer requirements for IMS VoLTE calls • “A default bearer must be created when the UE creates the PDN connection to the IMS well

known APN, as defined in 3GPP specifications. A standardised QCI value of five (5) must be used for the default bearer. It is used for IMS SIP signaling.”

• The network must initiate the creation of a dedicated bearer to transport the voice media. The dedicated bearer for Conversational Voice must utilise the standardized QCI value of one (1)

The requirement of a dedicated APN for IMS and defined QCI values for voice bearers allows for a consistent policy approach for all VoLTE calls.

If a consistent policy is applied to all subscribers for the IMS APN is

interaction with PCRF required for this APN?


Local Policy and PGW

Local policy is used today to generate dedicated bearers • Ex: Create a dedicated bearer with predefined “TFT” upon detection of RTP

• Operators using this for VoLTE POC trials to simplify trials

• Allows for a dedicated bearer to be created without querying the PCRF

Shortcomings to this approach • Must use “static” TFT with static QCI values

• Can not identify specific flow in granular detail (i.e. only using RTP traffic as event trigger)

• Flow can not be dynamically torn down in an efficient manner – wasted network resources (eNodeB)

• No SDP visibility (.ie. QCI requirements, media types, or conference call type scenarios

• No communication with IMS domain

PGW Service

Local Policy When RTP detected - event trigger to initiate dedicated bearer


PGW Service

P-CSCF Service

Local Policy

“Rx” “Gx”

Local Policy for VoLTE Collapsed P-CSCF/PGW Advantage When P-CSCF/PGW are co-located the P-CSCF can provide the flow details

(Media-Component-Description AVP) to the local policy engine.

The local policy engine uses this info to trigger the PGW service to dynamically setup/teardown network initiated bearers.

Result provides the network the same functionality as a PCRF would provide in much simpler more efficient manner

SDP Payload Trigger

Network initiated Bearer


Signaling Optimization: “local policy” for IMS APN - collapsed Rx/Gx

Rx Gx

UE

Gy

eNodeB

S11

Gi

Packet Data

Network

SPR

Mw

Provisioning

Billing

SGW/PGW

Cx

S1-MME

S1-U

MME

I/S-CSCF HSS

OCS PCRF

P-CSCF

Collapsed P-CSCF/PGW Architecture Collapsed P-CSCF/PGW Architecture

Local Policy Benefits for IMS APN

UE

Gy

eNodeB

S11

Gi

Packet Data

Network

SPR

Mw

Provisioning

Billing

SGW/PGW

Cx

S1-MME

S1-U

MME

I/S-CSCF HSS

OCS PCRF

P-CSCF

Rx

Gx Local Policy

With local policy

For the dedicated IMS APN: • Reduce interfaces and simplify architecture • Eliminate PCRF dependency for VoLTE calls • Reduce capacity on PCRF and DRA nodes • Reduce call set up times • Efficient routing of emergency calls

Additional Advantages of Collapsed P-CSCF/PGW


Additional Architectural Advantages Example: Remove “optional” pre-auth requirement

Eliminate need to “pre-auth” on SIP call setup reduces number of diameter transactions

P-CSCF /PGW mitigates need to “check” bearer policy during call setup


Additional Architecture Advantages E-CSCF, A-BG/P-CSCF

E-CSCF Deployment Flexibility • Ability to collapse E-CSCF on either P-CSCF, S-CSCF, or standalone

• Several interface or protocol options to integrate to existing GMLC

• Support for SIP/MAP interworking (mitigate needs to update LRF/GMLC)

• Retrieve location info from multiple sources prior to forwarding call

• Support VPLMN breakout for emergency calls

A-BG/P-CSCF Advantages • Local Hairpin media traffic – offload upstream MGW/BG ports

• Common policy enforcement point

• Single node for IP management (SIP and RTP NAT)

• Efficient solution to provide IPv4-IPv6 interworking support

• When UEs are IPv6 and the IMS core network is IPv4

• When UEs are IPv4 and the IMS core network is IPv6

Improve End User

experience

MGW/ BG

IPv4 UE

IPv6 UE

IPv4 Services

IPv6 Services

P-CSCF/ A-BG


Cisco Intelligent VoLTE Solution Ongoing Optimal Use of Network Resources

27

S1-MME S11

S1-U Gm

ISC

MSC (SR-VCC)

Sv

A/Iu

SR

-VC

C h

ando

ver

Mw

3GPP R10 23.237 introduces ATCF/ATGW - function in the serving network used for session control plane (ATCF) and media plan (ATGW) for the duration of the call before and after Access Transfer.

E-UTRAN

GERAN/ UTRAN

MME

SGW /PGW

mmTel TAS SCC AS

P-CSCF/A-BG P-CSCF/ A-BG I/S-CSCF

I2

Mw

ATGW

ATCF Mw

ATCF / ATGW

I2

RTP Endpoint

SIP Endpoint

SN HN


Additional Architecture Advantages Optimal Use of Footprint

0

5

10

15

20

25

30

35

40

45

1470

012

3140

1600

1624

8620

2958

9635

9176

4254

2446

6861

5246

8458

8798

6676

4379

9002

8916

2296

1178

1035

558

1118

316

1200

987

1282

939

1401

988

1474

234

1539

803

1578

175

1685

231

1705

067

1773

714

1831

891

1856

315

1868

587

1920

551

1967

262

1991

375

2012

159

% CPU (GGSN)

MEM GB (GGSN)

% CPU (GGSN+P-CSCF)

MEM GB (GGSN+P-CSCF)

Bearer traffic is started after bringing up the first 600,000 subscribers. That is the reason for the big jump in CPU (i.e. bearer throughput stated)

~3% Increase in CPU with addition of 1.5M P-CSCF

call model

GW Call Model • PDP Contexts: 2M (500/sec) • Avg DL/UL Packet Size 512/150 • Gx / Gy Rate: 512 / 512 TPS • HTTP Header enrichment: 100% of Traffic • Deep Packet Inspection: 100% of traffic • URI Rule List: 5,000 URI’s

P-CSCF Call Model • Total IMS Clients: 1.5 Million • IMS Client Registration Rate: 500/sec • Voice Call Rate: 500/sec • Call Hold Time: 60 sec


Additional Architecture Advantages Cx Interface Optimization

I-CSCF S-CSCF HSS

UAR/UAA

SAR/SAA

MAR/MAA

LIR/LAA

RTR/RTA

PPR/PPA

Optimal use of hardware footprint ‒ I/S-CSCF, BGCF – no “dedicated” blades

‒ Fully Standard Compliant

I/S-CSCF local cache ‒ Reduce number of LIR/LIA by maintaining a local cache

‒ Fast lookup to check if terminating subscriber on same S-CSCF

Configurable to not challenge UE during re-auth ‒ Enables call flow to bypass UAR/UAA, MAR/MAA exchange with HSS

S-CSCF Operator policy ‒ E.164 based prefix mechanism for HSS selection

‒ Multiple load sharing algorithms for ideal selection of multiple HSS.

Diameter message throttling towards all diameter peers ‒ Avoid overloading HSS/PCRF etc

Optimize signalling towards HSS


Key Takeaways

Cisco’s ability to collapse P-CSCF/PGW provides for significant reduction in diameter signaling

Flexible integration and use of local policy provides service providers implementation options

Optimized solution allows for simplified and expedited VoLTE deployment

The collapsed P-CSCF/PGW enables the IMS domain to become bearer aware. This allows for optimized network communication to accurately reflect the subscriber activity. The optimized footprint and intelligence enables operators to optimize SIP signaling and reduce diameter messages to the PCRF make most efficient use of available network resources.


Dedicated “IMS APN” LTE/EPC IP Flow Example

GTP

Default Bearer

UE eNodeB SGW

(BE)

PGW

Default Bearer

QCI 5 Default Bearer

Default Bearer

GTP

S5/S8 TEID A

S5/S8 TEID D

S1-TEID 1

IMS APN

S1-TEID 4 Off-net

Default Bearer

(BE) Default Bearer

GTP S5/S8 TEID E S1-TEID 5

On-net [Internet, Enterprise, etc]

Voice QCI1 Voice Dedicated Bearer

Dedicated Bearer

GTP S5/S8 TEID B S1-TEID 2

UL T

FT

DL T

FT

Video QCI6 Video Dedicated Bearer

Dedicated Bearer

GTP S5/S8 TEID C S1-TEID 3

UL T

FT

DL T

FT

[Internet, Enterprise, etc]

IMS APN

epc architectured2zmdbbm9feqrf.cloudfront.net/2012/usa/pdf/brkspm-3515.pdf · epc architecture:...

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