Download - 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).
Single-radio voice call continuity (SR-VCC)
Single-radio voice call continuity (SR-VCC)
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.
Single-radio voice call continuity (SR-VCC)
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.
Single-radio voice call continuity (SR-VCC)
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.
Voice call transfer from E-UTRAN to UTRAN/GERAN
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.
Voice call transfer from E-UTRAN to UTRAN/GERAN
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
Voice call transfer from E-UTRAN to CDMA2000 1xRTT
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.
Voice call transfer from E-UTRAN to CDMA2000 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
Voice path after handover completion
1xRTT traffic allocation
4. Domain transfer successful
Voice call handling with fallback to 2G/3G
Voice call handling with fallback to 2G/3G
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).
Voice call handling with fallback to 2G/3G
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.
Voice call handling with fallback to 2G/3G
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
Voice path after handover completion
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
Voice path after handover completion
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
IMS-based voice call continuity
IMS-based voice call continuity
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).
IMS-based voice call continuity
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-based voice call continuity
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