LTE - Voice Call Handover

Voice Call Handover Mechanisms inNext-Generation 3GPP Systems

Apostolis K. Salkintzis, MotorolaMike Hammer, CiscoItsuma Tanaka, NTT DOCOMOCurt Wong, Nokia Siemens Networks

LTE Workshop – Day 2Session 6

Prepared by Mervat Abu-Elkheir

Today’s Sessions

Voice Call Handover Mechanisms in Next-Generation 3GPP

Systems - Mervat

QoS Control in the 3GPP Evolved Packet System – Hatem

Network-Based Mobility Management in the Evolved 3GPP Core

Network – Hung

Interference Coordination and Cancellation for 4G Networks -

Hassan

Outline

Overview of the next-generation 3GPP systems

Single-radio voice call continuity (SR-VCC)

Voice call transfer from E-UTRAN to UTRAN/GERAN

Voice call transfer from E-UTRAN to CDMA2000 1xRTT

Voice call handling with fallback to 2G/3G

IMS-based voice call continuity

News Flash! LTE is here!

On December 14, 2009, the first commercial LTE deployment was in the Scandinavian capitals Stockholm and Oslo by the Swedish-Finnish network operator TeliaSonera and its Norweigan brand name NetCom (Norway).TeliaSonera branded the network "4G".

News Flash! LTE is here!

The modem devices were manufactured by Samsung, and the network infrastructure created by Huawei (in Oslo) and Ericsson (in Stockholm). TeliaSonera used spectral bandwidth of 10 MHz, and Single-Input and Single-Output transmission.This would provide physical layer net bitrates of up to 50 Mbit/s downlink and 25 Mbit/s in the uplink.TeliaSonera plans to roll out nationwide LTE across Sweden, Norway and Finland.

Overview of the next-generation 3GPP systems

2G/3G 3GPP core

3GPP EPC

Overview of the evolved 3GPP networkMSC

SGSN

MSC

MME

P-GWS-GW

HSS

Packet data

network(s)

UTRAN

GERAN

E-UTRAN

EIu-cs

Iu-ps

Gb/Iu-psA/Iu-cs

S3

S5S1-U

S6a

S4

UE

SGi

Legacy circuit-

switched services

GGSNGn

PCRFePDG

CDMA2000

HRPDWiMA

XWLAN

Gi

S11S1-AP

STa S2a

Gxa

Gxc

GxbS2b

SWn

S101 S103

Gx

Overview of the evolved 3GPP network

3GPP-specific access technologies are connected through the

serving gateway (S-GW).

Trusted non-3GPP specific access technologies are connected

through the packet data network gateway (P-GW).

Untrusted non-3GPP specific access technologies are connected

through the evolved packet data network gateway (ePDG).



During initial deployment of E-UTRAN, it will have limited

coverage where wireless broadband services are most needed.

Seamless handover of voice calls between E-UTRAN and

UTRAN/GERAN coverage areas is crucial to achieve continuity of

voice services.


Challenges are:

Voice calls on E-UTRAN are carried only via IP-based technologies, so

voice calls have to be transferred between CS and IMS service domains.

Voice calls have to be transferred across service domains with single-

radio mobile terminals that cannot support simultaneous signaling on

both E-UTRAN and UTRAN/GERAN.


3GPP standards address two solutions for enabling single-radio

voice call continuity (SR-VCC)

Handover from E-UTRAN to UTRAN/GERAN

Handover from E-UTRAN to CDMA2000 1xRTT

Current standards do not support handover from UTRAN/GERAN

or CDMA2000 1xRTT to E-UTRAN.


All voice calls initiated at E-UTRAN are anchored at the IMS.

At least one MSC server in the CS domain is enhanced with

interworking functionality and a new interface; Sv.

MME has additional functionality to support the Sv interface and

the SR-VCC procedures.

The standard supports handover of voice and non-voice sessions

that might be active in parallel.


Handover process should create voice interruption of no more

than a few hundreds of milliseconds for a seamless voice

transfer.

Non-voice sessions cannot be guaranteed to be seamless due to

UTRAN/GERAN’s limited bandwidth.

2G/3G 3GPP core

3GPP EPC

Architecture for single-radio VCC between E-UTRAN and UTRAN/GERAN

MSC

SGSN MSC enhanced for SR-VCC

MME

P-GWS-GW

HSS

IMS

UTRAN

GERAN

E-UTRAN

E

Iu-cs

Iu-ps

Gb/Iu-ps

A/Iu-cs

DSvS3

S6a

S5S1-U

S11

S4UE

SGi

Message Flow Diagram for single-radio handover between E-UTRAN and UTRAN/GERAN

UE E-UTRAN MME EnhancedMSC MSC Remote

endIMSGERAN orUTRAN

S-GW/P-GWSGSN

1. Measurement reportsHandover decision

2. Handover required3a. Request reservation of PS resources

3b. Request reservation of CS resources

3c. PS resources reserved3d. CS resources reserved

4. Initiation of session transfer (STN-SR)

IMS session transferprocedures5. Handover command

UE moves to GERAN

6. Handover detection7a. PS handover complete

7b. Update bearer8. CS handover complete

Voice path before handover

Voice path after handover completion

Voice packets from remote end forwarded to enhanced MSC

MME splits voice bearers from non-voice bearers and initiates

their relocation towards the MSC and SGSN

Voice gap

last a few

hundred ms


A 1xCS interworking solution (IWS) function is required in the

3GPP2 CS domain to interwork with EPS using a new interface;

S102.

The 1xCS IWS enables the UE to communicate with 1xRTT MSC

while connected to EPC via E-UTRAN.

This allows the UE to establish the target CS access leg while still

on E-UTRAN access prior to actual handover to 1xRTT.


MME requires functionality to support the S102 interface.

MME relays signaling between the UE and 1xCS IWS.

The standard handles only the voice part of an IMS session.

3GPP2 core

3GPP EPC

Architecture for single-radio VCC between E-UTRAN and 3GPP2 1xRTT CS

1xRTTMSC

1xCSIWS

MME

P-GWS-GW

HSS

IMS

1xRTTCS

access

E-UTRAN

A1A1

S102

S6a

S5S1-U

S11

UE

SGi

HLR

MAP

Message Flow Diagram for voice session handover from E-UTRAN to 3GPP2 1xRTT CS access

UE E-UTRAN MME 1xCSIWS

1xRTTMSC

Remote endIMS1xRTT

CS accessS-GW/P-GW

1. Measurement reports

Handover decision2. Handover request (start 1x SRVCC)3. Start SRVCC CDMA2000 tunnelling

4. Initiate domain transfer 3GPP2 VCCVoice call transfer

procedures5. 1x Handoff CMD

UE moves to 1xRTT

Handover detection6. Release UE context

7. Suspend EPS bearer

Voice path before handover


1xRTT traffic allocation

4. Domain transfer successful



In some initial deployments of the evolved 3GPP systems there

will be no support for voice services on E-UTRAN.

To provide voice services to users, fallback to legacy 2G/3G

networks is needed.

This fallback is a service-based handover mechanism triggered

by a service request (e.g. originating or terminating voice call).


Fallback to the 2G/3G CS domain is enabled by:

Combining 2G/3G mobility management with EPS mobility

management.

Delivering paging requests for terminating calls to the UE via EPS.

Using 2G/3G for paging responses and further call handling for

terminating calls.

Using 2G/3G for handling all originating calls.


The UE attaches to the MME in EPC and to an MSC in the 2G/3G

CS domain by conducting a combined EPS/IMS attach procedure.

A mapping is performed by the MME between E-UTRAN tracking

areas and 2G/3G location areas.

When the UE moves to E-UTRAN, its 2G/3G location area is

updated in order to successfully deliver incoming calls.

2G/3G 3GPP core

3GPP EPC

Architecture for 3GPP CS Fallback to UTRAN/GERAN

SGSN

MSC enhanced for CSFB

MME

P-GWS-GW

HSS

Packet data

network

UTRAN

GERAN

E-UTRAN

Iu-cs

Iu-ps

Gb/Iu-ps

A/Iu-csD

SGs

S3

S6a

S5S1-U

S11

S4UE

SGi

Message Flow Diagram for mobile originating call for CS fallback (UE in active mode)

UE E-UTRAN MME UTRAN/ GERAN

S-GW/P-GWSGSN

1. Service request2a. S1-AP message with CS fallback indicator

3. Packet-switched handover

4a. SABM (Connection Management service request)

If the MSCIs changed

5a. Service reject

UE moves to 2G/3G

6. CS call establishment procedure

7a. Forward relocation complete7b. Forward relocation complete ack

8a. Update PDP context request

IP packet path before handover


EnhancedMSC

2b. Optional measurement report solicitation

4b. Complete layer 3 info (with CM service request)4c. UA (with CM service request)

5b. Service reject

5c. Location area update

8b. Update PDP context response

9. Routing area update procedureIf the routingarea is changed

IP packet path after handover

Message Flow Diagram for mobile terminated call for CS fallback (UE in active mode)

UE E-UTRAN MME UTRAN/ GERAN

S-GW/P-GWSGSN

1a. Paging1b. Paging

4. Packet-switched handover

5a. SABM (with paging response)

If the MSCIs changed

6a. Connection reject

UE moves to 2G/3G

7. CS call establishment procedure

8a. Forward relocation complete8b. Forward relocation complete ack

9a. Update PDP context request

IP packet path before handover


EnhancedMSC

3b. Optional measurement report solicitation

5b. Complete layer 3 info (with paging response)5c. UA (with paging response)

6b. RRC release

6c. Location area update and roaming retry

9b. Update PDP context response

10. Routing area update procedureIf the routingarea is changed

IP packet path after handover

2a. Service request2b. CS page reject

3a. S1-AP message with CS fallback indicator



Voice call continuity mechanisms are provided by the IMS as part

of its goal to maintain services when the user is moving across

different access networks and terminal types.

VCC mechanisms enable the support of voice continuity

between the 3GPP-specific access and the non-3GPP access (e.g.

WLAN).


There are two solutions to provide voice service continuity via

IMS:

Voice call continuity (VCC) between an access network supporting CS

voice (e.g. GSM, UMTS, CDMA2000 1xRTT) and a VoIP access network

(e.g. WLAN)

Service centralization and continuity (SCC) to provide enhanced call

transfer and service centralization in the IMS.


There are two solutions to provide voice service continuity via

IMS:

Voice call continuity (VCC) between an access network supporting CS

voice (e.g. GSM, UMTS, CDMA2000 1xRTT) and a VoIP access network

(e.g. WLAN)

Service centralization and continuity (SCC) to provide enhanced call

transfer and service centralization in the IMS.

IMS components

IMS service continuity architecture based around the SCC-AS

CS phon

e

I/S/P-CSCF

MGC

IMS phon

e

Circuit

switchI/S-

CSCF

SCC-AS (3PCC)

AAA/HSS/HLR

MGC

P-CSCF

3Gphon

e

2Gphon

e

PSTNphon

e

3GMSC

2GMSC

PSTNSSP

SIPclient

SIPclient

SIPclient

4Gphon

e

WiFiAP

WiMAX

ASN

SIPIP-PBX

4Gaccess

UE

PSTN

2G

3G

EPS

WiMAX

WiFi

Possiblecomboof types

Enterprise

Remote leg

Access leg

Message Flow Diagram for voice call transfer with IMS service continuity mechanisms

UEGERAN

MSC withIMS centralized

ServicesWLAN EPC Remote ISDN

phonePSTN/ISDN

networkCSCFs SCCAS

Setup STN-SR

Additional signalling path following transfer

Signaling path prior to transfer

Voice path following transfer

Re-INVITE (remote, SDP-MGW/MSC

MGCFMGWWLAN CS

INVITE (STN, SDP-MGW/MSC) INVITE

Re-INVITE

Voice (and data) path prior to transfer

PSTN/ISDN leg is unchanged

To wrap up

At the initial stages of evolved 3GPP network deployment, E-

UTRAN may not have extensive coverage.

SR-VCC mechanisms are defined to maintain an ongoing voice

call when the UE moves out of E-UTRAN coverage.

Voice call fallback mechanisms to CS domain are defined at the

beginning of a voice call when E-UTRAN does not yet support

voice services.

To wrap up

Voice call continuity by IMS is defined for voice call transfer

when voice services are supported on E-UTRAN and non-3GPP-

defined radio accesses.

IMS can support voice call continuity among different access

technologies with the same VCC procedures.

Thank you

Documents

LTE - Voice Call Handover