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Emphasizing the IMS core network• Ultimate goal: all network elements are IMS capable• All network services are provided via IMS– Existing basic call and supplementary services– New multi-media services (MMTel, Video etc.)• Allows legacy UE access– Best effort service delivery – up to the UE capability– Access adaptation – allows non-IMS UE to gain access to IMS network Leading to future• Achieve the fix mobile convergence (FMC) goal• Unified core network and services, diversified access methods– IMS core and IMS centered multi-media services– IMS access via wireless or wire-line accesses– Non-IMS legacy accesses Challenges• Service continuity– Across different networks– Deal with different UEs, especially non-IMS capable ones• Service consistency– IMS services shall be consistently provided using different network accesses
Citation preview
3
IMS Centralized Services (ICS) Highlights
� Emphasizing the IMS core network
• Ultimate goal: all network elements are IMS capable
• All network services are provided via IMS
– Existing basic call and supplementary services
– New multi-media services (MMTel, Video etc.)
• Allows legacy UE access
– Best effort service delivery – up to the UE capability
– Access adaptation – allows non-IMS UE to gain access to IMS network
� Leading to future
• Achieve the fix mobile convergence (FMC) goal
• Unified core network and services, diversified access methods
– IMS core and IMS centered multi-media services
– IMS access via wireless or wire-line accesses
– Non-IMS legacy accesses
� Challenges
• Service continuity
– Across different networks
– Deal with different UEs, especially non-IMS capable ones
• Service consistency
– IMS services shall be consistently provided using different network accesses
4
IMS Centralized Services (ICS) Architecture
IMS
PSTNPSTN WLAN
(IP-CAN)
WLAN
(IP-CAN)
GSMGSMCable DSL
(IP-CAN)
Cable DSL
(IP-CAN)
Access Networks
Circuit
Switch
Network
Circuit
Switch
Network
Core Network
User Equipments
6
IMS Centralized Services (ICS) Requirements
� Services
• Service control always performed by home IMS network
• Service providers can be– Home IMS network
– Visited IMS network
– 3rd party provider
• Service coverage– IMS supplementary services (3GPP TS 24.173)
– Other provider specific IMS services
• Service delivery– Best effort: deliver the service up to UE and access network capabilities
� Support for legacy devices
• No absolute need to upgrade to IMS UEs to receive ICS
• Service offerings to legacy UEs will be limited
� Support for roaming
• ICS need to support the following roaming cases– Roaming within the home network
– Roaming between home and visited networks (subject to roaming agreement)
– Roaming between different access networks (GSM/UMTS, WLAN, Wireline Broadband etc.)
• In case of ICS is not or only partially supported by roaming partners– Only the subset of ICS services are provided or
– Only basic call services are supported or
– Roaming to these networks is barred
7
IMS Centralized Services (ICS) Requirements
� Service Continuity
• Service continuity shall be sustained as much as possible across different access networks
• User device and access network capabilities may have constraints on service continuity
� Service Consistency
• Services hosted in IMS shall be available via any access networks– A reduced set of ICS may be offered subject to constrains of the access network
– Call independent services (e.g. Cal Forwarding) shall be supported
– Emergency calls shall be supported
– Priority services for ICS users are desired.
8
IMS Centralized Services (ICS) Key Network Elements
� UE
• ICS UE
• Non-ICS UE
� MSC Server
• Enhanced for ICS
• Not enhanced for ICS
� IM CN Entities
• x-CSCF
• Other element (?)
ICS UE A MSC Server IM CN Entities SCC AS UE B
� SCC AS• Service Centralization & Continuity Application
Server
• An ICS AS
• Roles:
– ICS User Agent (IUA)
– CS Access Adaptation (CAA)
– Terminating Access Domain Selection (T-ADS)
– I1 Service Control Signalling Termination
• Functionalities
– Registration
– Call / SS control / convergence
– Service continuity support
10
IMS Centralized Services (ICS) SCC AS
� SCC AS is a Home network element
• provides functionality required to enable IMS Centralized Services.
• in the session path using originating and terminating Initial filter criteria (iFC)
– the first AS in the originating iFC chain
– the last AS in the terminating iFC chain
• May be invoked through the use of PSI termination procedures when using CS access.
� SCC AS main roles
• ICS User Agent (IUA): provides SIP UA behaviour on behalf of the UE
• CS Access Adaptation (CAA): provides interworking functions for CS UE access to IMS network elements
• Terminating Access Domain Selection (T-ADS):
– Directs an incoming session to an ICS User
– For one or more UEs of an ICS User:
» Influences the selection of one or more contacts amongst the registered contacts
» Influences the selection of an access network for delivery of the incoming session to the
selected contact
» Performs breakout to the CS Domain by fetching the CSRN.
• I1 Service Control Signalling Termination :
11
IMS Centralized Services (ICS) SCC AS
� SCC AS major Functionalities
• Provide service consistency support
– Registration
– Call convergence
– Supplementary services convergence
• Provide service continuity support
– Single Radio Voice Call Continuity (SRVCC) support
� handoff
– IMS Service Continuity support
� PS – CS service continuity
� PS – PS service continuity
� Inter UEs transfer
12
IMS Centralized Services (ICS) SCC AS
YesYesYes, only if I1 is
supported
As driven by
operator
policy and
VPLMN
support.
As driven by
operator
policy and
VPLMN
support.
YesNoRequired
T-ADSIUACAAGmI1
SCC ASTransparent control channelICS UEMSC Server with ICS
enhancements
ICS function support needs in different deployment scenarios
• An operator who only supports UEs that have ICS functionality for their ICS Users
• An operator who only supports non ICS UEs for their ICS Users
YesConditional*NoNoNoNoYesRequired
T-ADSIUACAAGmI1
SCC ASTransparent control channelICS UEMSC Server with ICS
enhancements
• An operator who supports UE’s for their ICS Users that do / do not have ICS functionality
YesYesYes, if I1 is
supported
As driven by operator
policy and
VPLMN support.
As driven by operator
policy and
VPLMN support.
YesYesRequired
T-ADSIUACAAGmI1
SCC ASTransparent control channelICS UEMSC Server with ICS
enhancements
13
IMS Centralized Services (ICS) SCC AS
� SCC AS Interfaces
• I1: ICS UE access to SCC AS via CS (for service control signalling)
– I1 reference point is optional and implemented using USSD transport via CS
network elements.
• Gm: ICS UE access to SCC AS via PS (through CSCF/ISC)
• I2: Non-ICS UE access to SCC via CS (through MSC Server enhanced for ICS
and CSCF/ISC)
IMS Service Centralization and Continuity Reference Architecture
14
IMS Centralized Services (ICS) SCC AS
� ICS UE �������� SCC AS Signaling paths
• Service control signaling path:
– Used to transport service control signalling between ICS UE and SCC AS
– For enabling IMS services via CS or PS access
– Used when needed
• CS bearer control signaling path:
– Used to transport media bearer control signaling
– For managing service required bearer media resources.
� What SCC AS does in controlling services
• Acting as a B2BUA
• Combines the service control signalling and CS Bearer Control Signalling to
form the Access Leg
• Using IMS signaling to interact with CSCF on behalf of UE as the remote Leg
15
IMS Centralized Services (ICS) SCC AS
� SCC AS Accessing Option 1: Sessions established using Gm
• Using Gm over PS network for Service Control Signalling Path
16
IMS Centralized Services (ICS) SCC AS
� SCC AS Accessing Option 2: Sessions established using I1
• Using I1 via CS network for Service Control Signalling Path
17
IMS Centralized Services (ICS) SCC AS
� SCC AS Accessing Option 3: Sessions established using CS call control and
MSC Server
19
IMS ICS SCC AS Control Flows : Registration
UE IMS registration when using an MSC Server enhanced for ICS
21
IMS ICS SCC AS Control Flows: Basic MO Call
ICS UE origination with CS media using Gm when using an MSC Server enhanced for ICS
22
IMS ICS SCC AS Control Flows: Basic MO Call
ICS UE origination with CS media using Gm when using an MSC Server NOT enhanced for ICS
23
IMS ICS SCC AS Control Flows: Basic MO Call
CS UE origination when using an MSC Server enhanced for ICS — multiple codecs used
24
IMS ICS SCC AS Control Flows: Basic MO Call
CS UE origination when using an MSC Server enhanced for ICS – one codec used
25
IMS ICS SCC AS Control Flows: Basic MO Call
CS UE origination when using an MSC Server not enhanced for ICSU E V M S C M G C F
I n t e r m e d i a t e I M
C N s u b s y s t e m
e n t i t i e s
S C C A S
2 . S E T U P
3 . O r i g i n a t i o n
t r i g g e r s
5 . I S U P / B I C C I A M
7 . S I P I N V I T E
9 . R e t r i e v e
o r i g i n a l c a l l i n g
a n d c a l l e d p a r t y
i n f o r m a t i o n
8 . S I P 1 0 0
( T r y i n g )
1 0 . S I P I N V I T E
1 2 . S I P I N V I T E
1 3 . S I P 1 0 0
( T r y i n g )
1 1 . S I P 1 0 0
( T r y i n g )
1 5 . S I P 2 0 0 ( O K )
1 6 . S I P 2 0 0 ( O K )
1 7 . S I P 2 0 0 ( O K )
1 9 . I S U P / B I C C
A N M
2 4 . S I P A C K
2 5 . S I P A C K
2 6 . S I P A C K
2 0 . C O N N E C T
2 1 . C O N N A C K
1 . D e t e r m i n a t i o n o f
c a l l e s t a b l i s h m e n t
d o m a i n
C S b e a r e r I M S b e a r e r
M G W
6 . S I P I N V I T E
1 4 . 1 8 0 ( R i n g i n g ) , I S U P / B I C C A C M a n d A L E R T I N G
1 8 . S I P 2 0 0 ( O K )
2 2 . S I P A C K
2 3 . H . 2 4 8 i n t e r a c t i o n w i t h
t h e M G W
4 . R e d i r e c t i o n t o
I M C N s u b s y s t e m
27
IMS ICS SCC AS Control Flows: Basic MT Call
Termination to a CS UE registered in IMS using an MSC Server enhanced for ICS – multiple codecs used
29
IMS ICS SCC AS Control Flows: Basic MT Call
Termination to an ICS UE with CS media using Gm reference point when using an MSC server enhanced for ICS
30
IMS ICS SCC AS Control Flows: Basic MT Call
Termination to an ICS UE with CS media using Gm when using an MSC Server not enhanced for ICS
33
IMS ICS SCC AS Control Flows: Supplementary Services
Explicit Communication Transfer using Gm reference point, ICS UE as transfer recipient
35
IMS ICS SCC AS Control Flows: Supplementary Services
Communication Waiting via the MSC Server enhanced for ICS
37
IMS ICS SCC AS Control Flows: Supplementary Services
Communication Forwarding on Busy User flow over the I1
38
IMS ICS SCC AS Control Flows: Supplementary Services
Communication Forwarding No Reply flow over the I1
39
IMS ICS SCC AS Control Flows: Supplementary Services
Communication Forwarding Not Reachable flow over the I1
S-CSCFTASSCC ASMSC ServerICS UE B UE A
4. INVITE
1. INVITE
2. INVITE
3. INVITE
5. User not reachable
7. SIP response (user unreachable)
6. SIP response (user unreachable)
8. CFNRc Logic
40
IMS ICS SCC AS Control Flows: Supplementary Services
Communication Deflection flow over the I1
S-CSCFTASSCC ASMSC ServerICS UE B UE A
9. SIP Response (C-party)
4. INVITE
1. INVITE
7. I1: Call Deflection Request (C-party)
8. SIP Response (C-party)
2. INVITE
3. INVITE
5. I1: Incoming Call
6. User Deflects Call
10. CD Logic
42
� Main focus
• SRVCC between E-UTRAN access and 3GPP2's 1xCS
• SRVCC between E-UTRAN access and UTRAN/GERAN accesses
• SRVCC between UTRAN (HSPA) access and UTRAN/GERAN accesses
� All for Circuit Switched (CS) calls that are anchored in the IMS
� SCC AS serves the IMS Service Continuity control functions
IMS ICS SCC AS Service Continuity: SRVCC
43
IMS ICS SCC AS Service Continuity: SRVCC
SRVCC from E-UTRAN to 3GPP2 1xCS
U E M M E1 x C SIW S
1 x R T TM S C
1 x R T T
C S a c c e s sE -U T R A N
1 a . I M S E m e r g e n c y S e s s i o n o n g o i n g o v e r E -U T R A N a c c e s s
1 b . M M E i n d i c a t e s to E -U T R A N t h a t C N a n d U E a r e S R V C C
c a p a b l e
2 . M e a s u r e m e n t
R e p o r t s
3 . S R V C C H a n d o v e r t o C D M A 2 0 0 1 x
i s r e q u i r e d a s d e f i n e d i n T S 2 3 . 2 1 6
4 . I n i t i a t e s I n t e r -T e c h n o l o g y E m e r g e n c y S R V C C H a n d o v e r
6 . E m e r g e n c y v o i c e o n g o i n g c a l l o v e r th e C S l e g e s t a b l i s h e d o v e r 1 x R T T a c c e s s
7 . H a n d o v e r
e x e c u t i o n
5 . 1 x t r a f f i c a s s i g n m e n t & 3 G P P 2 e m e r g e n c y
V C C p r o c e d u r e
8 . R e c o n f i g u r e L o c a t i o n S u p p o r t
46
IMS ICS SCC AS Service Continuity: SRVCC Flow
SRVCC from E-UTRAN to GERAN without DTM support
U E S o u rc e E -U T R A N
S o u r c e M M E
M S C S e r v e r / M G W
T a rg e t M S C
1 4 . H a n d o v e r C o m m a n d
T a r g e t B S S
1 . M e a s u r e m e n t re p o r ts
3 . H a n d o v e r R e q u ir e d
S G W
2 . D e c is io n fo r H O
5 .P S to C S R e q
6 .P r e p H O R e q
7 . H O R e q u e s t /A c k
8 .P r e p H O R e s p
9 . E s ta b l is h c i rc u it
1 9 . H O C o m p le te
2 0 .S E S (H O C o m p le te )
2 1 . A N S W E R
1 3 .P S t o C S R e s p
1 5 . H O f r o m E U T R A N c o m m a n d
H S S /
H L R
2 3 .U p d a te L o c
1 0 . In i t ia t io n o f S e s s io n T r a n s fe r ( IS U P / S T N -S R o r E -S T N -S R )
1 1 . S e s s io n t r a n s fe r a n d U p d a te re m o te e n d
IM S (S C C A S )
1 2 . R e le a s e o f IM S a c c e s s le g
2 2 . P S t o C S C o m p le te /A c k
T a r g e t S G S N
1 6 . U E tu n e s to G E R A N
1 7 . H O D e te c t io n
1 8 . S u s p e n d ( s e e T S 2 3 .0 6 0 )
1 8 . S u s p e n d 1 8 . S u s p e n d R e q u e s t / R e s p o n s e
1 8 . U p d a te B e a r e r
4 . B e a r e r S p li t t in g
G M L C 2 4 . S u b s c r ib e r L o c a t io n R e p o r t
47
IMS ICS SCC AS Services Continuity: SRVCC
SRVCC from E-UTRAN to UTRAN or GERAN with DTM HO support
1 3 . H a n d o v e r C o m m a n d
1 . M e a s u r e m e n t r e p o r t s
3 . H a n d o v e r R e q u i r e d
2 . D e c i s io n fo r H O
5 a . P S t o C S R e q
1 7 a . R e lo c /H O C o m p le t e
1 7 b . S E S ( H O C o m p le t e )
1 7 c . A N S W E R
1 2 . P S t o C S R e s p
1 8 a . R e lo c /H O C o m p le t e
1 8 c . U p d a te b e a r e r
H S S /
H L R 1 7 e . U p d a t e L o c
5 b . P r e p H O R e q
8 b . P r e p H O R e s p
8 c . E s t a b l is h c i r c u i t
6 a . F o r w a r d R e lo c R e q 6 b . R e lo c / H O R e q
5 c . R e lo c /H O R e q
8 a . R e lo c /H O R e q A c k
7 b . F o r w a r d R e lo c R e s p
7 a . R e lo c / H O R e q A c k
1 1 . R e le a s e o f IM S a c c e s s l e g
1 0 . S e s s io n t r a n s f e r a n d u p d a te r e m o t e l e g
9 . I n i t ia t i o n o f S e s s io n T r a n s f e r ( I S U P : S T N - S R o r E - S T N - S R )
U E S o u r c e E - U T R A N
S o u r c e M M E
M S C S e r v e r / M G W
T a r g e t M S C
T a r g e t R N S /B S S
S G W IM S ( S C C A S )
T a r g e tS G S N
1 4 . H O f r o m E U T R A N c o m m a n d
1 7 d . P S t o C S C o m p le t e /A c k
1 8 b . F o r w a r d R e lo c C o m p le te /A c k
1 6 . H O D e t e c t i o n
4 . B e a r e r S p l i t t i n g
1 5 . U E t u n e s t o U T R A N /G E R A N
G M L C 1 9 . S u b s c r i b e r L o c a t io n R e p o r t
48
IMS ICS SCC AS Control Flows: Services Continuity
SRVCC from UTRAN (HSPA) to GERAN without DTM support
U E S o u r c e
U T R A N ( H S P A )
S o u r c e S G S N
M S C S e r v e r / M G W
T a r g e t M S C
1 4 . R e lo c a t i o n C o m m a n d
T a r g e t B S S
1 . M e a s u r e m e n t r e p o r t s
3 . R e lo c a t io n R e q u i r e d
G G S N
2 . D e c i s io n f o r H O
5 . P S t o C S R e q
6 . P r e p H O R e q
7 . H O R e q u e s t /A c k
8 . P r e p H O R e s p
9 . E s ta b l i s h c i r c u i t
1 9 . H O C o m p le te
2 0 . S E S ( H O C o m p le te )
2 1 . A N S W E R
1 3 . P S t o C S R e s p
1 5 . H O f r o m U T R A N c o m m a n d
4 . B e a r e r S p l i t t in g
H S S /
H L R
2 3 . U p d a t e L o c
1 0 . I n i t i a t i o n o f S e s s io n T r a n s f e r ( I S U P : S T N - S R o r E - S T N - S R )
1 1 . S e s s io n t r a n s f e r a n d U p d a t e R e m o te e n d
IM S ( S C C A S )
1 2 . R e le a s e o f IM S a c c e s s l e g
2 2 . P S t o C S C o m p le te / A c k
T a r g e t S G S N
1 6 . U E t u n e s t o G E R A N
1 7 . H O D e t e c t io n
1 8 . S u s p e n d ( s e e T S 2 3 . 0 6 0 )
1 8 . S u s p e n d 1 8 . S u s p e n d R e q u e s t / R e s p o n s e
1 8 . U p d a t e B e a r e r
G M L C 2 4 . S u b s c r ib e r L o c a t io n R e p o r t
49
IMS ICS SCC AS Services Continuity: SRVCC
SRVCC from UTRAN (HSPA) to UTRAN or GERAN with DTM HO support
13. Relocation Command
1. Measurement reports
3. Relocation Required
2. Decision for HO
5a. PS to CS Req
17a. Reloc/HO Complete
17b. SES (HO Complete)
17c. ANSWER
12. PS to CS Resp
18a. Reloc/HO Complete
18c. Update bearer
HSS/
HLR 17e. UpdateLoc
5b. Prep HO Req
8b. Prep HO Resp
8c. Establish circuit
6a. Forward Reloc Req 6b. Reloc / HO Req
5c. Reloc /HO Req
8a. Reloc/HO Req Ack
7b. Forward Reloc Resp
7a. Reloc/HO Req Ack
11. Release of IMS access leg
10. Session transfer and Update Remote end
9. Initiation of Session Transfer (ISUP: STN-SR or E-STN-SR)
UE Source UTRAN (HSPA)
SourceSGSN
MSC Server/ MGW
Target MSC
Target RNS/BSS
GGSN IMS (SCC AS)
TargetSGSN
14. HO from UTRAN command
17d. PS to CS Complete/Ack
18b. Forward Reloc Complete/Ack
16. HO Detection
4. Bearer Splitting
15. UE tunes to UTRAN/GERAN
GMLC 19. Subscriber Location Report
51
IMS ICS SCC AS Services Continuity: IMS SC
� Main focus
• Access Transfer – enabling service continuity between access networks
– PS-CS Access Transfer
– PS-PS Access Transfer
– PS-PS Access Transfer in conjunction with PS-CS Access Transfer
– Adding and/or removing media flows to support service
– MSC Server assisted mid-call feature
– SRVCC session transfer of IMS emergency session
• Inter-UE transfer
– Establishment and release of a Collaborative Session
– Transfer of media flows to a target UE whilst keeping Collaborative Session control
in the Controller UE
– Transfer of all media flows to a target UE without establishing a Collaborative
Session
• All transfer procedures are executed and controlled by SCC AS
� Solutions for service continuity using IMS procedures
� SCC AS serves as SIP-AS in the signaling path of all IMS sessions
53
IMS ICS SCC AS Services Continuity: IMS SC Flow
Signalling flow for PS-CS Access Transfer: CS to PS
54
IMS ICS SCC AS Services Continuity: IMS SC Flow
Signalling flow for PS-CS access transfer: PS to CS
56
IMS ICS SCC AS Services Continuity: IMS SC Flow
Signalling flow for PS - PS in conjunction with PS - CS Access Transfer: PS to CS
57
IMS ICS SCC AS Services Continuity: IMS SC Flow
Signalling flow for PS - PS in conjunction with PS - CS Access Transfer: CS to PS
58
IMS ICS SCC AS Services Continuity: IMS SC Flow
Remote End Initiation case – Removing media from split CS and PS sessions
59
IMS ICS SCC AS Services Continuity: IMS SC Flow
Signaling flow for inter UE transfer without Collaborative Session establishment H P L M N o f t h e t e r m i n a t i n g U EH P L M N o f t h e o r i g i n a t i n g U E
S C C A S
M e d i a p a t h b e t w e e n U E - 1 a n d U E - 3
I n t e r m e d i a t e I M
C N s u b s y t e m
e n t i t i t i e sU E - 2
I n t e r m e d i a t e I M
C N s u b s y t e m
e n t i t i t i e sU E - 1 U E - 3
1 . U E - 1 i s o n a n a c t i v e m u l t i m e d i a s e s s i o n w i t h U E - 3 . C a l l i s a n c h o r e d i n S C C A S
2 . S I P R E F E R
3 . i F C E v a l u a t i o n
4 . S I P R E F E R
2 5 . S I P 2 0 0 I N V I T E
1 2 . S I P I N V I T E
1 5 . R e m o t e L e g U p d a t e
I M S S e r v i c e C o n t r o l
6 . S I P R E F E R
1 6 . S I P r e - I N V I T E
1 7 . S I P r e - I N V I T E
1 8 . S I P r e - I N V I T E
1 9 . S I P 2 0 0 r e - I N V I T E
2 0 . S I P 2 0 0 r e - I N V I T E
2 1 . S I P 2 0 0 r e - I N V I T E
2 3 . S I P A C K
2 7 . S I P A C K
2 9 b . M e d i a p a t h b e t w e e n U E - 2 a n d U E - 3
2 2 . S I P A C K
3 8 . S I P B Y E
3 9 . S I P B Y E
4 0 . S I P 2 0 0 B Y E
2 4 . S I P A C K
2 9 a . I M S S e r v i c e C o n t r o l
7 . S I P R E F E R
8 . S I P 2 0 2 R E F E R
9 . S I P 2 0 2 R E F E R
1 0 . S I P 2 0 2 R E F E R
1 1 . S I P 2 0 2 R E F E R
1 4 . S I P I N V I T E
2 6 . S I P 2 0 0 I N V I T E
2 8 . S I P A C K
3 2 . S I P N O T I F Y ( S I P
2 0 0 )
3 0 . S I P N O T I F Y ( S I P
2 0 0 ) 3 1 . S I P N O T I F Y ( S I P
2 0 0 )
3 3 . S I P N O T I F Y ( S I P 2 0 0 )
3 4 . S I P 2 0 0 N O T I F Y
3 5 . S I P 2 0 0 N O T I F Y
3 6 . S I P 2 0 0 N O T I F Y
3 7 . S I P 2 0 0 N O T I F Y
4 1 . S I P 2 0 0 B Y E
1 3 . i F C E v a l u a t i o n
5 . R E F E R r e q u e s t a u t h o r i z a t i o n
60
IMS ICS SCC AS Services Continuity: IMS SC Flow
Release of Collaborative Session initiated by Controller UE
61
IMS ICS SCC AS Services Continuity: IMS SC Flow
Signaling flow for PS-CS Transfer: CS to PS with MSC server assisted mid-call feature
62
IMS ICS SCC AS Services Continuity: IMS SC Flow
Signaling flow for PS-CS Transfer: PS to CS with MSC server assisted mid-call feature
63
References
� 3GPP TS 23.292 V9.3.0 (2009-09) IP Multimedia Subsystem (IMS) centralized services Stage 2
� 3GPP TS 24.292 V9.1.0 (2009-09) Multimedia (IM) Core Network (CN) subsystem Centralized Services
(ICS) Stage 3
� 3GPP TS 23.216 V9.1.0 (2009-09) Single Radio Voice Call Continuity (SRVCC) Stage 2
� 3GPP TS 23.237 V9.2.0 (2009-09) IP Multimedia Subsystem (IMS) Service Continuity Stage 2
� 3GPP TS 24.237 V9.0.0 (2009-09) IP Multimedia Subsystem (IMS) Service Continuity Stage 3