LTE Voice Services

Agenda

• Voice Options in LTE

• Comparison of Voice Options

• Voice Deployment Strategies

• MultiService Forum

• VoLTE Recent Announcements

• Voice Enhancements – Rel 8 & 9

• Conclusion

Voice Options with LTE

• Data Only

• Circuit Switched Fallback (CSFB) to 2G/3G CS

• VoLGA

• VoLTE (IMS-based) – On LTE Only – On LTE & 2G/3G via SR-VCC – On LTE & 3G via UMTS PS

• Over-the-top (OTT) – à la Skype

Data Only • PROS

– Simple – Device availability – Easy and gradual deployment of

LTE

• CONS – Not useful for smartphones – Single radio limitation – May encourage OTT competition

The initial LTE offering for many carriers is based on devices with no native voice support - eg PC Dongles

CS Fallback Procedures - 1

• Registration:

– a combined UE registration procedure on both LTE and GSM/UMTS – from the MME to the MSC via the SG interface – GSM/UMTS Location Area ID (LAI) calculated from the LTE Tracking

Area ID (TAI)

• Call Origination

– UE requests the MME to perform a CSFB – MME requests the eNodeB to redirect UE to the target 2G/3G cell

(determined via UE measurements or preconfigured) – The eNodeB redirects the UE to the target cell – The UE performs an RRC on the target cell (and possibly a location

update as well)

CS Fallback Procedures - 2 • Call Termination:

– The MSC sends the page request to the MME over the SG interface – The MME pages the UE with the CSFB indicator – UE responds with a service request with the CSFB indicator – MME instructs the eNodeB to redirect UE to the target 2G/3G cell

(determined via UE measurements or preconfigured) – The eNodeB redirects the UE to the target cell – The UE performs an RRC on the target cell (and possibly a location update as

well)

• Active Data Sessions: – Must be handed-over to the 2G/3G or dropped – Via a Packet Switch HandOver (PSHO) on 3G – Requires Dual Transfer Mode (on both 2G and UE) if fallback on 2G

CS Fallback Procedures - 3

• SMS: – No fallback for SMS origination/termination – UE sends/receives SMSs to/from the MME – MME sends/receives SMSs to/from the MSC over

the SG interface

CS Fallback Architecture

UE eNodeB S-GW P-GW

PCRF MME

IMS

HSS

GERAN

MSC/VLR UTRAN

S1-MME

LTE Uu

X2

S1-U

S10 S11

SGs

S5 SGi

S7 RX+

S6a Ch, Sx

Um

Uu

CS Fallback Call Flow

MSC SGSN BSS

2. Optional Measurement Report Solicitation

4b. A/Iu-cs message (with CM Service Request) 4b. CM Service Request

If the MSC is changed

Location Area Update or Combined RA/LA Update

5. CM Service Reject 5. CM Service Reject

eNodeB MME 1a. Extended Service Request

UE S-S-GW P-GW

UE

3a. PS HO as specified in 23.401 [2] (preparation phase and start of execution phase)

6. CS call establishment procedure

1b. S1-AP Request message with CS Fallback indicator

7. PS HO as specified in 23.401 [2] (continuation of execution phase)

1c. S1-AP Response message

4a. Location Area Update or Combined RA/LA Update

3c. Update Bearer(s) 3b. Suspend

UE to MME: I want to move to UTRAN

MME to ENB: UE wants to move to UTRAN

ENB to UE: where are you?

if PS HO fails -» CSFB fails ONLY FOR GERAN

The call is established on 3G Once the call is ended, PS HO to LTE

SGSN deactivates GBR Bearers (SGW+PDN)

LA in UE is nok? Then LAU

UE to MSC: Context Modification

CS Fallback – UE and Network Requirements • UE:

– Support for both LTE and GSM/UMTS– Support for combined EPS/IMSI attach, detach, and location update procedures– Support for CS fallback and SMS procedures

• Network – 2G/3G MSCs:– Support of SGs interface to the MME– Support of simultaneous paging on the A, Iu, and SGs interfaces– Support of sending and receiving SMS over the SGs interface

• Network – LTE MME:– SGs interface support– MSC procedures such as IMSI attach/detach, location update, and paging– CS fallback SMS procedures

• Network – LTE E-UTRAN:– Redirect UE to a GSM/UMTS cell– Forwar

• Network Engineering– Additional LTE traffic over the GSM/UMTS network (RAN and MSC)– Tracking/location and coverage areas shall be consistent between LTE and GSM/UMTS

CSFB issue due to TA/LA misalignment

Source : GSMA IR.88 LTE Roaming Guidelines

In the case of TA/LA misalignment, the Roaming Retry procedure allows transferring the incoming call from MSC1 to MSC2, which increases both

the call setup time and the call success ratio.

CS Fallback – PROs & CONs

• PROS– Reuse of all GSM/UMTS voice infrastructure including existing

OSS/BSS systems– Fast rollout of voice services– Voice service transparency between LTE and 2G/3G– Minor upgrades on legacy network (SG interface similar to the MSC-

SGSN Ginterface)

• CONS– Call set-up delay i.e. 500+ msec– Concurrent data session may be dropped

VoLGA • Based on 3GPP TS 23.879 option

2, with further development bythe VoLGA Forum

• Uses a new dedicatedInterworking Function (IWF), alsoknown as VoLGA Access NetworkController (VANC), to interworkthe LTE and GSM/UMTSnetworks. Inserted between theEPS and MSC

• All voice traffic goes through theLTE but using the 2G/3G voiceinfrastructure in a transparentmanner

Source: 3GPP VoLGA Stage 2 V2.0.0 (2010-06-14)

VoLGA • PROS

– Reuse of all GSM/UMTS voice infrastructure including existing OSS/BSSsystems

– Fast rollout of voice services– Voice service transparency between LTE and 2G/3G– No changes on legacy network– Fast LTE-to-GSM/UMTS handovers– Supports concurrent voice and data sessions

• CONS– Voice traffic hits both the LTE and the 2G/3G networks– Introduces three new network elements: VANC, security GW, AAA server– Does not support advanced IMS services– Not accepted by 3GPP

IMS – Historical Overview • Rationale & Purpose

– IMS is an SIP-based (Session Initiation Protocol) session and service control platform that enables delivery ofmultimedia applications across a broadband wireline or wireless network

– IMS was first introduced in the 3GPP Release 5 standards and predates the development of LTE by nearly seven years– Builds on IETF SIP technology (perceived Internet scaling and low cost)– Split the access network from the service network permitting common service network across fixed, mobile and

internet– Multimedia in addition to voice; No need to standardised services only enablers

• The Reality– IMS was intended to be access agnostic, but interaction with existing technologies requires access specific

functionality be added to the IMS network.– Complex standard with many options to SIP– Large legacy service load; Service parity with CS is complicated– Commercial systems available, but take up has been very slow– 3GPP extensions in 3GPP TS 24.229 for management, security and billing reasons

• Initial Deployment Issues– Cost – IMS requires a complete new core network– Risk – Scaling up to support 10’s of millions to subscribers is still an unknown.– Performance is also seen as a risk– Integration – Existing services have to be integrated with IMS based service– Operator business models – Services run as separate P&L centres

IMS – Key Components The Call Session Control Functions (CSCF) are the core components of the IMS. There are three CSCF: • Proxy-CSCF (P-CSCF): The P-CSCF is the

first point of contact for a user. The PCSCF behaves like a proxy, i.e. it accepts requests and forwards them on.

• Interrogating-CSCF (I-CSCF): The I-CSCF is the entry contact within an operator’s network for all connections destined to a subscriber.

• Serving-CSCF (S-CSCF): The S-CSCF is responsible for handling the registration process, making routing decisions, maintaining sessions, and downloading user information and service profiles from the HSS.

VoLTE with LTE Access Only • Based on 3GPP TS 23.228 IMS

supporting both legacy voiceservices and advanced multi- media services

• GSMA IR.92 defines the profilefor Voice and SMS based on OneVoice Initiative

• Can be extended to support voiceservice service continuity to 2GGSM network (i.e. handovers)

• Can be extended to support voiceservice service continuity to 3GUMTS/HSPA network (i.e.

UE eNode B S-GW P-GW

PCRF MME

HSS

P-CSCF

S-CSCF I-CSCF

AF

IMS

VoLTE with SRVCC-based voice delivery

• SIP signaling between the UE andthe IMS core

• Over the existing transportcapabilities of the GSM/UMTSnetwork

• Use of ICS (CS-to-IMS call control)and SRVCC (handovers)

• Support simultaneous PS and CSservices, the IP connection isprovided by the legacy packetcore as per the Gm referencepoint.

3GPP TS 23.216 V9.6.0 (2010-12): "Single radio voice call continuity (SRVCC); Stage 2 (Release 9)".

VoLTE with UMTS-PS voice delivery

• UMTS PS access, allowing voice,data and multimedia services tobe carried simultaneously overthe same PS-domain IPconnection (no need for ICS andSRVCC)

• Concurrent voice and datamultimedia services

• Seamless mobility between theLTE and UMTS networks with theuse of PS handovers andhandbacks

UE E- UTRAN P-GW

MME

3GPP IMS

HSS

UE UTRAN GERAN MSC

SGSN

Uu

S1-MME

S1-U

S11

S6a

SGis

SV

S3

Iu-CS/A Um/Uu

Iu-PS/Gb I2

VoLTE Procedures - 1

• Registration:– The UE always registers on the IMS network (for both LTE and

GSM/UMTS)– Registration includes the ICS and SRCVCC indicators (if supported)

• Call Origination– Session is set-up as standard IMS procedures according to 3GPP TS

23.228 – In the GSM/UMTS, the ICS-enabled UE sets-up 2 signaling paths (one

over legacy packet to the IMS SCC AS, one CS-bearer via legacyprocedures to the MSC)

– The SCC AS combines the 2 procedures on the CS-access leg andestablishes the IMS-leg of the call

VoLTE Procedures - 2 • Call Termination:

– IMS terminating session is initiated toward the UE’s selected contact address– Upon receiving the invite message, the ICS-enabled UE originates a CS call to

the SCC AS using its associated directory number– Similar procedure as for call origination

• LTE to UMTS PS Handover:– Initiated by the eNode B via a request to the MME to establish resources in

the target RNC, SGSN and SGW– The MME only needs to coordinate and perform a PS handover. Because both

the voice and non-voice sessions are over PS, there is no separate CS sessionto hand over

• Direct tunnel from the SGW to the RNC via an S12 interface• Indirect tunnel from the SGW to the SGSN to the RNC

VoLTE Procedures - 3 • SRVCC-based handovers: SRVCC enables calls to be seamlessly handed over from

the LTE to the GSM/UMTS access network, while session/call control remains inIMS.– Initiated by the E-UTRAN to the MME based on the measurement reports it receives

from SRVCC-enabled Ues– The MME then separates out the voice bearer from the non-voice bearers and starts the

handover procedure with both the MSC and SGSN– MSC instructs the target Radio Network Subsystem (RNS) to prepare for the handover by

allocating the necessary resources to set-up the CS access leg– the MSC initiates the IMS session transfer to the CS domain (3GPP TS 23.292 and TS

23.237) – When complete, the CSCF switches the VoIP call to the CS access leg that has been

established for the handover.– It notifies the MME that it is ready for handover– The MME instructs the E-UTRAN to handover

VoLTE Procedures - 4

• SMS.– requires the use of the IP Short Message Gateway (IP-SM-GW), asdefined by 3GPP TS

23.204 Release 7. This gateway is required for SMS message delivery between the SMS Center and any IP-based UE

– IP-SM-GW receives a message from the SMS Center, it forwards it tothe CSCF, which in turn delivers it to the UE

– the IP-SM-GW may deliver SMS messages using the IMS, PS or CSdomains

– the UE receives its SMS on the IMS, UMTS or GSM network– The IP-SM-GW attempts SMS delivery in the order set by the operator

policy and/or user preferences. For example, the IP-SM-GW may firstattempt SMS delivery on the LTE/IMS network, followed by the packetcore, and finally by the circuit core.

VoLTE – UE and Network Requirements • VoLTE with LTE access only

– IMS core — CSCF, Telephony Ap•plication Server (TAS), and other components– UE supporting VoLTE client– SIM cards (UICC) supporting the ISIM application– an IP-SM-GW is required for the support of SMS.

• VoLTE with LTE and UMTS PS access– upgrades to the UTRANs in the GSM/UMTS network– Optional upgrade to the SGSNs for the indirect tunneling– The UTRAN not only requires an upgrade to 3GPP Release 8, but must also support Robust Header Compression

(ROHC) and a radio allocation process that offers semi-persistent scheduling.– The UTRAN must also support the S12 interface between the RNC and SGW used for the direct tunneling method.– The SGSN must also be upgraded to 3GPP Release 8 to support the S4 interface to the SGW. This interface is used for

the indirect tunneling method.

• VoLTE with ICS and SRVCC– UE support of the ICS and SRVCC clients.– On the IMS network, two IMS application servers: SCC AS and SRVCC AS.– For VoLTE GSM support, the SCC AS along with the MSC and Home Location Register (HLR) must support USSD.– SRVCC also requires upgrades to the E-UTRAN, MME and HSS in the LTE network.– To support SRVCC handovers, the MSC must be upgraded with the Sv interface and must support coordination of the

SRVCC relocation and session transfer procedures. Upon successful relocation, the MSC must also be able toautomatically register the UE with the HLR.

– The HLR may also need upgrading to support the new IP-SM-GW in the network.

VoLTE – PROs & CONs • PROS

– IMS enables new revenue generating, advanced voice and data blended services (e.g.GSMA Rich Communication Suite (RCS))

– Efficient concurrent voice and data handovers UMTS PS access– With ICS and SRVCC, voice service transparency between LTE and 2G/3G– Preserves LTE’s bandwidth during voice calls while minimizing call setup delay– Assures global interoperability and roaming– Provides the largest possible ecosystem which affects such matters as handset supply

and multivendor interworking– Provides an all-IP network for operational savings and HD voice

• CONS– Sizable investment in the LTE on IMS core — CSCF, TAS, IP-SM-GW– With ICS and SRVCC, the SCC and SRVCC ASs are required as well as SRVCC upgrades to

the E-UTRAN and MME, the deployment of an MGCF and upgrades to all border MSCsfor support of the Sv interface.

– Possible break in the voice stream when a session/call is handed down to theGSM/UMTS network

Over-The-Top (OTT) • Fills the gaps in carrier voice strategy• OTT technically viable on LTE and UMTS• Apps-stores make it easy for users to install clients• PROS

– Not limited by legacy continuity– Preserve LTE data rates during voice calls– No “IMS complexity tax”– Integration with presence and productivity apps– Non-traditional voice apps (Voice Twitter?)– Support of wideband voice– Competitive pricing

• CONS– Business case unproven– QoS management unclear– DPI blocking possible– Roaming challenges with data roaming charges & QoS control– Global interoperability with the PSTN– Availability outside LTE footprint unclear– Regulation

Network Impact - ComparisonRequirement VoLTE

LTE Only VoLTE UMTS PS VoLTE ICS and SRVCC

New network equipment

None • VANC

• Security gateway• AAA server

• IMS core

• IP-SM-GW

• IMS core

• IP-SM-GW

• IMS core

• IP-SM-GW• SCC and SRVCC AS

• MGCFLegacy network upgrades

All MSCs overlaying LTE coverage

None None •UTRAN•SGSN for indirecttunneling method

• Only MSCs at LTE edge

• HLR

EPS and/or IMS upgrades

• E-UTRAN

• MME

• E-UTRAN

• MME

• HSS • HSS • E-UTRAN

• MME• HSS

3GPP compliance for IOT ease

Yes No •Standards advancedby VoLGA Forum

Yes Yes Yes

Terminal changes Likely small

• CS-fallback support

Likely substantial

• VoLGA support• SRVCC support

Likely small

• IMS client

Likely small

• IMS client

Likely substantial

• IMS client• ICS support

• SRVCC supportLTE and GSM/UMTS coverage engineering considerations

•Requires LTE andGSM/UMTS coverage overlap •Similar configuration fortracking and location areas

None None None None

CS Fallback VoLGA

Performance - Comparison Requirement CS Fallback VoLGA VoLTE

LTE Only VoLTE UMTS PS VoLTE ICS and SRVCC

Network providing voice services GSM/UMTS GSM/UMTS IMS IMS IMS

Network providing voice radio coverage GSM/UMTS LTE LTE UMTS GSM/UMTS

Network providing SMS GSM/UMTS, but user remains on the LTE

network

GSM/UMTS, but user remains on the LTE

network LTE/IMS network LTE/IMS network LTE/IMS network

Quality of voice call set- up Some delay Excellent Excellent Excellent Excellent

Quality of LTE-to- GSM/UMTS voice

handovers N/A Excellent – CS based N/A Excellent, PS-based Possible break in voice

stream with SRVCC handover

Support for in-call handbacks No No No Yes Yes: 3GPP Release 10

Support for concurrent voice and data • No for GSM

• Yes for UMTS Yes Yes Yes Yes

Support for advanced services No No Yes Yes Yes

Operational benefit of flat all-IP network

No: LTE access and IMS not used

Partial: uses LTE access, but not IMS Yes Partial: uses IMS, but

UMTS PS access Partial: uses IMS, but

GSM/UMTS access

VoLTE and Roaming

UE Options (by priority)

Visited LTE Network Options (by priority)

CSFB VoLTE VoLTE+CSFB

CSFB CSFB – CSFB

VoLTE – VoLTE VoLTE

VoLTE+ CSFB CSFB VoLTE VoLTE

Recommendations Requirement CS Fallback VoLTE

LTE Only VoLTE UMTS PS VoLTE ICS and SRVCC

Operator with LTE network with complete national coverage

√

GSM operator starting to deploy LTE √ √ √

UMTS operator starting to deploy LTE √ √ √

Operator planning to deploy UMTS VoLTE √ √

Operator with GSM/UMTS and CDMA networks √ √ √

Operator with wireline and wireless networks √ √ √

Operator offering or planning to offer advanced IMS services

√ √ √

LTE Voice Deployment Strategies

LTE

2G/3G

LTE 3G

2G

LTE 3G

2G

LTE 3G

2G

Step 1: Spotty LTE Coverage: CSFB across the 2G/3G coverage area

Step 2a: VoLTE Launch: UMTS PS across 2G/3G coverage area

Step 2b: VoLTE Launch: SR-VCC across 2G coverage area

Step 3: Full VoLTE Coverage Target Solution New terminals use LTE only Legacy terminals on legacy networks

MultiService Forum (MSF) VoLTE Interoperability Event 2011

Event backed by the GSMA to validate a number of GSMA technical recommendations, namely: • PRD IR.65 - IMS Roaming and

Interworking Guidelines,• PRD IR.88 - LTE Roaming

Guidelines,• PRD IR.92 - IMS Profile for Voice

and SMS.

http://www.msforum.org/

VoLTE – Early Adopters (Aug 2012)

• US carrier MetroPCS claims to have beaten SK Telecom to the title of “world’s first VoLTE(Voice-over-LTE) operator”, as commercial deployment in this space starts to ramp up.

• South Korea’s SK yesterday issued a statement saying that the launch today of its HD Voiceservice will see it become the first operator in the world to commercially switch on VoLTEservices. However, MetroPCS has stolen SK’s thunder slightly by saying that it switched on itsown service yesterday, ahead of SK. The US operator is now selling the VoLTE-capable LGConnect 4G Android smartphone at “select US stories” and says it will “continue to roll outVoLTE services and phones in the coming weeks.” SK’s launch today is supported by theSamsung S3 smartphone.

• Meanwhile South Korean number three operator LG Uplus is also switching on its VoLTEservice today in Seoul, supported by LG’s Optimus LTE2 smartphone. The country’s second- largest operator, KT, has said it plans to launch VoLTE in October.

• Separate reports this week claim US operator T-Mobile USA is now considering supportingVoLTE services sometime in the future, a move that will follow similar launches by AT&T andVerizon Wireless.

VoLTE – Joyn Brand

• T-Mobile, Vodafone launch Joyn-branded RCS services inGermany – Aug 2012-March 2013

• Free app on iOS and Android• Based on GSMA Rich Communication Suite (RCS)• Already available in Spain – Telefonica & Vodafone• Available in fixed network later• 1 M Joyn Subs - SK Telecom Feb 2013• 30 operators in 18 countries are committed to Joyn – GSMA

Jan 3013

Joyn Service Launches Country Operator Launch Date Device support

Germany T-Mobile Mar 2012 Android 2.3+ and iOS apps

S Korea SK Telecom Dec 2012 Android 2.3 app iOS app slated early 2013 app

S Korea KT Freetel Dec 2012 Android 2.3 app iOS app slated early 2013

S Korea LG U+ Dec 2012 Android 2.3 iOS slated early 2013

Spain Orange Nov 2012 Android v2.2+ and iOS, Samsung Galaxy SIII, LG Optimus L9, One S HTC,

Nokia Lumia 920, Sony Xperia Z Spain Movistar Nov 2012 As Above

Spain Vodafone Nov 2012 As Above

USA MetroPCS Oct 2012 Android v2.2+

Germany Vodafone Aug 2012 Android v2.2+ and iOS

Voice Enhancements

• Release 8– Semi-Persistent Scheduling (SPS)– TTI Bundling.

• Release 9– Emergency services– Location services

Conclusion – Determining Factors

• Timing of the LTE network launch: near or far future• LTE coverage: complete or partial national coverage• Type of network currently deployed: GSM, UMTS, fixed/mobile converged,

GSM/UMTS/ CDMA converged, UMA, or IMS• Planned network upgrades to UMTS, VoLTE with UMTS HSPA+, or other

technologies• Timing for the introduction of new advanced multimedia services• Decision to implement an interim solution or go straight to the end-goal

solution• Voice over LTE options/option combinations of roaming partners

Relevant Standards 3GPP • 23.204: IP-SM-GW• 23.216: Single Radio Voice Call Continuity (SRVCC)• 23.221: Architectural requirements• 23.228: IP Multimedia Subsystem (IMS)• 23.237: IMS Service Continuity (ISC)• 23.272: CS Fallback• 23.292: IMS Centralized Services (ICS)• 22.173: IMS Supplementary Services• 23.401: GPRS Enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Access• 23.879: Study on Circuit (CS) Domain Services over Evolved packet Switched (PS) AccessGSMA • PRD IR.65 - IMS Roaming and Interworking Guidelines,• PRD IR.88 - LTE Roaming Guidelines,• PRD IR.92 - IMS Profile for Voice and SMS• PRD IR.64 - IMS Service Centralization and Continuity Guidelines

THANK YOU