chapter 3: ip multimedia subsystems and application-level signaling
TRANSCRIPT
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.
Chapter 3: IP Multimedia Subsystemsand Application-Level Signaling
Jyh-Cheng Chen and Tao Zhang
IP-Based Next-Generation Wireless NetworksPublished by John Wiley & Sons, Inc. January 2004
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.2
This material is protected under all Copyright Laws as they currently exist. ©2004 Jyh-Cheng Chen and Tao Zhang, and John Wiley & Sons, Inc. All rights reserved. Notwithstanding user’s ability to use and modify the PowerPoint Slides, it is understood that the original version of these slides, as well as any and all modifications thereof, and all corresponding copyrights, shall at all times remain the property of Jyh-Cheng Chen and Tao Zhang, and John Wiley & Sons, Inc.
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.3
Outline
3.1 Signaling in IP Networks3.2 3GPP IP Multimedia Subsystem (IMS)3.3 3GPP2 IP Multimedia Subsystem (IMS)
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.4
3.1 Signaling in IP Networks
3.1.1 Session Initiation Protocol (SIP)3.1.2 Session Description Protocol (SDP)
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.5
3.1.1 Session Initiation Protocol (SIP)
SIP is an application-layer protocol that can establish, modify and terminate multimedia sessions (conferences) over the Internet.SIP messages could contain session descriptions such that participants can negotiate with media types and other parameters of the session. SIP provides its own mechanisms for reliability and can run on top of several different transport protocols such as TCP, UDP and SCTP (Stream Control Transmission Protocol).
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.6
SIP Capabilities
Determine destination user’s current locationDetermine whether a user is willing to participate in a sessionDetermine the capabilities of a user’s terminal.Set up a sessionManage a session. This includes modifying the parameters of a session, invoking service functions to provide services to a session, and terminating of a session.
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.7
SIP Components
SIP user agent (UA) user agent client (UAC) user agent server (UAS)
SIP redirect server: UASSIP proxy server: UAC and UASSIP registrar: UAS Location service
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SIP
3.1.1.1 Naming and Addressing3.1.1.2 Messages3.1.1.3 Location Registration3.1.1.4 Session Establishment and Termination
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3.1.1.1 Naming and Addressing
SIP Uniform Resource Identifier (URI) sip:[email protected] sips:[email protected] sip:user:password@host:port;uri-
parameters?headers sip:+886-3-574-
2961:[email protected];user=phone sip:[email protected]?subject=Wiley%20Boo
k&priority=urgent sip:wire.cs.nthu.edu.tw
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.10
URI Parameters
parameter-name=parameter-valuetransport: UDP, TCP, SCTP, TLS, etc. transport=udp is equivalent to Transport=UDP
maddr: indicate a proxy that must be traversed to the destination maddr=140.114.79.60
ttl: used only when the maddr is a multicast address and the transport protocol is UDPuser: distinguish a real telephone number from a user name that resembles a telephone numbermethod: specifies the method of the SIP URI requestlr: used when a specific SIP routing mechanism is implemented (will not discuss further)
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.11
3.1.1.2 MessagesINVITE: Used by a user to invite another user to establish a SIP sessionACK: Used to confirm final responseBYE: Used to terminate a sessionCANCEL: Used to cancel a SIP requestOPTIONS: Used to query servers about their capabilitiesREGISTER: Used by a user to register information with a serverINFO: Used to carry session related control informationSUBSCRIBE: Used to request current state and state updates from a remote nodeNOTIFY: Used to notify a SIP node that an event which has been requested by an earlier SUBSCRIBE method has occurredPRACK: Used to provide a reliable Provisional Response ACKnowledgementUPDATE: Used to update parameters of a sessionMESSAGE: Used to transfer Instant Messages (IM)REFER: Used to direct a recipient to other resource by using the contact information provided in the REFER request
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.12
Message Format
A start-line Request-Line Status-Line
One or more header fieldsAn empty line indicating the end of the header fieldsAn optional message body
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Table 3.1 Structure of a SIP message
Start-line INVITE sip:[email protected] SIP/2.0Header Field(s) Via: SIP/2.0/UDP fly.cs.nthu.edu.tw:5060;branch=z9hG4bK776asdhds
Max-Forwards: 70To: Tao <sip:[email protected]>From: Jyh-Cheng <sip:[email protected]>;tag=1928301774Call-ID: [email protected]: 123456 INVITEContact: <sip:[email protected]>Content-Type: application/sdpContent-Length: 132
Empty LineMessage Body v=0(Optional) t=2873397496 2873404696
m=audio 49170 RTP/AVP 0……
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Status-LineStatus-Code 1xx: Provisional – indicate a request is received and is being
processed. 2xx: Success – indicate the method invoked by a request is
successfully accepted. E.g. SIP/2.0 200 OK
3xx: Redirection – further action needs to be taken by the sender of the corresponding sender in order to complete the request.
4xx: Client error – the request contains syntax error or cannot fulfilled at this server.
5xx: Server error – the server failed to fulfill an apparently valid request.
6xx: Global failure – the request cannot be fulfilled at any server.
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.15
3.1.1.3 Location Registration
Address of the registrar Preconfigured address-of-record sip:[email protected] will send
REGISTER to sip:research.telcordia.com Multicast address In IPv4, 224.0.1.75 has been allocated to
sip.mcast.net
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Tao’s UAC
tao-pc.research.telcordia.com
Registrar
registrar.research.telcordia.com
REGISTER
200 OK
Fig. 3.1 SIP registration
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.17
Example of REGISTER
REGISTER sip:registrar.research.telcordia.com SIP/2.0Via: SIP/2.0/UDP tao-pc.research.telcordia.com:5060;
branch=z9hG4bKnashds7Max-Forwards: 70To: Tao <sip:[email protected]>From: Tao <sip:[email protected]>Call-ID: 843817638423076@989sddhas09CSeq: 2660 REGISTERContact: <sip:[email protected]>Expires: 3600Content-Length: 0
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.18
Example of OK
SIP/2.0 200 OKVia: SIP/2.0/UDP tao-pc.research.telcordia.com:5060;
branch=z9hG4bKnashds7;received=128.96.60.187To: Tao <sip:[email protected]>From: Tao <sip:[email protected]>Call-ID: 843817638423076@989sddhas09CSeq: 2660 REGISTERContact: <sip:[email protected]>Expires: 3600Content-Length: 0
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.19
3.1.1.4 Session Establishment and Termination
Peer-to-peer mode a caller establishes a call to a callee directly
without going through any SIP serverServer mode Proxy server
forward the received SIP request toward its final destination on behave of the originator
may rewrite specific parts of the message before forwarding it
Redirect server respond to a request with the callee’s contact
information to indicate where the caller should contact next
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.20
cs.nthu.edu.tw
jcchen@fly
flygreenhouse
location server
tao-pc
research.telcordia.com
INVITE [email protected]
tao
200 OK
200 OK
tao@tao-pc
tao@
tao-
pc
INVITE tao@tao-pc
12 3
ACK [email protected] tao@tao-pc
46
7
8 9
5 Ringing
Fig. 3.2 SIP in proxy mode
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INVITE INVITE sip:[email protected] SIP/2.0Via: SIP/2.0/UDP
fly.cs.nthu.edu.tw:5060;branch=z9hG4bK776asdhdsMax-Forwards: 70To: Tao <sip:[email protected]>From: Jyh-Cheng <sip:[email protected]>;tag=1928301774Call-ID: [email protected]: 123456 INVITEContact: <sip:[email protected]>Content-Type: application/sdpContent-Length: 132
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.22
200 OKSIP/2.0 200 OKVia: SIP/2.0/UDP greenhouse.research.telcordia.com:5060;
branch=z9hG4bKnashds8;received=207.3.230.150Via: SIP/2.0/UDP fly.cs.nthu.edu.tw:5060;
branch=z9hG4bK776asdhds;received=140.114.79.59To: Tao <sip:[email protected]>;tag=a6c85cfFrom: Jyh-Cheng <sip:[email protected]>;tag=1928301774Call-ID: [email protected]: 123456 INVITEContact: <sip:[email protected]>Content-Type: application/sdpContent-Length: 121
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.23
ACK
ACK sip:[email protected] SIP/2.0Via: SIP/2.0/UDP fly.cs.nthu.edu.tw:5060;
branch=z9hG4bK776asdhdsMax-Forwards: 70To: Tao <sip:[email protected]>;
tag=a6c85cfFrom: Jyh-Cheng <sip:[email protected]>;
tag=1928301774Call-ID: [email protected]: 123456 ACKContent-Length: 0
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.24
BYE
BYE sip:[email protected] SIP/2.0Via: SIP/2.0/UDP tao-pc.research.telcordia.com;
branch=z9hG4bKnashds10Max-Forwards: 70From: Tao <sip:[email protected]>;
tag=a6c85cfTo: Jyh-Cheng <sip:[email protected]>;
tag=1928301774Call-ID: [email protected]: 231 BYEContent-Length: 0
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.25
cs.nthu.edu.tw
jcchen@fly
fly
location server
INVITE [email protected]
tao
tao@
wire
.cs.n
thu.
edu.
tw
1
2 3
302 Moved TemporarilyContact: [email protected]
4
5ACK [email protected]
wiretao@wire
6 7INVITE [email protected]
200 OK 8
9ACK [email protected]
cs.nthu.edu.tw
greenhouse
research.telcordia.com
Ringing
Fig. 3.3 SIP in redirect mode
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.26
3.1.2 Session Description Protocol (SDP)
Designed to describe multimedia sessions convey information of media streams so
prospective participants of multimedia sessions could learn the relevant setup information
Does not incorporate any transport protocol a common usage of SDP is to embed SDP in the
payload of other protocols
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Format
<type>=<value>
Name and purpose of the sessionActivation time of the sessionMedia comprising the sessionInformation, such as address, port number, and format, to receive the media
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Example
v=0o=jcchen 2890844526 2890842807 IN IP4
140.114.79.59s=Wiley Booki=Discussion on book writingc=IN IP4 224.2.17.12/127t=2873397496 2873404696m=audio 49170 RTP/AVP 0m=video 51372 RTP/AVP 31m=application 32416 udp wb
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.29
Offer/Answer Model
For unicastTo find common codecs both participants can supportEither one of the participants may generate a new offer message to update the sessionMandatory for SIP
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Offer (in INVITE)
v=0o=Jyh-Cheng 2890844526 2890844526 IN IP4
fly.cs.nthu.edu.tws=c=IN IP4 fly.cs.nthu.edu.twt=0 0m=audio 49170 RTP/AVP 0m=video 51372 RTP/AVP 31m=application 32416 udp wb
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.31
Answer (in 200 OK)
v=0o=Tao 2890844730 2890844730 IN IP4 tao-
pc.research.telcordia.coms=c=IN IP4 tao-pc.research.telcordia.comt=0 0m=audio 49920 RTP/AVP 0m=video 0 RTP/AVP 31m=application 32416 udp wb
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.32
3.2 3GPP IP Multimedia Subsystem (IMS)
3.2.1 IMS Architecture 3.2.2 Mobile Station Addressing for Accessing the IMS 3.2.3 Reference Interfaces3.2.4 Service Architecture 3.2.5 Registration with the IMS3.2.6 Deregistration with the IMS 3.2.7 End-to-End Signaling Flows for Session Control
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.33
3.2.1 IMS Architecture
Support real-time voice and multimedia IP applicationsUse SIP to support signaling and session control Call State Control Function (CSCF): a SIP server Serving CSCF (S-CSCF) Proxy CSCF (P-CSCF) Interrogating CSCF (I-CSCF)
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IMS
McMg
Mj Mi
Mb
Mb
Cx
Mm
PSTN
Traffic connectionsSignaling connections
C, D,Gc, Gr
MwMr
MkMk
PSTN
Mb Mp
CSCFMGCF
BGCFBGCF
HSS
MRFC
IM-MGW
MRFPP-CSCF PCF
Go
GGSN
PSTN
IPNetwork
SignalingNetwork
or Legacy
Wireless Networks
Mw
CSCF
SLF
UE
Dx
Gm
Fig. 3.4 3GPP IP multimedia subsystem
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Serving CSCF (S-CSCF)Registration: A S-CSCF can act as a SIP Registrar to accept users’ SIP registration requests and make users’ registration and location information available to location servers such as the HSS.Session Control: A S-CSCF can perform SIP session control functions for a registered user. Proxy Server: A S-CSCF may act as a SIP Proxy Server that relays SIP messages between users and other CSCFs or SIP servers.Interactions with Application Servers: A S-CSCF acts as the interface to application servers and other IP or legacy service platforms.Other functions: A S-CSCF performs a range of other functions not mentioned above. For example, it provides service-related event notifications to users and generates Call Detail Records (CDRs) needed for accounting and billing.
Copyright © 2004 by John Wiley & Sons, Inc. All rights reserved.36
Proxy CSCF (P-CSCF)
A mobile’s fist contact point inside a local (or visited) IMSAct as a SIP Proxy Server accept SIP requests from the mobiles and then
either serves these requests internally or forwards them to other servers
Include a Policy Control Function (PCF) that controls the policy regarding how bearers in the GGSN should be usedPerform a range of other functions
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Interrogating CSCF (I-CSCF)
An optional function that can be used to hide an operator network’s internal structure from an external network Serve as a central contact point within an operator’s network for all sessions destined to a subscriber of that network or a roaming user currently visiting that networkSelect an S-CSCF for a user’s session based on capabilities required by the user capabilities and availability of the S-CSCFs topological information such as the location of an S-CSCF
and the location of the users’ P-CSCFs Route SIP requests to the selected S-CSCFGenerate CDRs
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Other ComponentsMedia Gateway Control Function (MGCF) and IM Media Gateway (IM-MGW) responsible for signaling and media interworking between PS
and CS domainsMultimedia Resource Function Processor (MRFP) control the bearer on the Mb interface process the media streams
Multimedia Resource Function Controller (MRFC) interpret signaling information from an S-CSCF or a SIP-
based Application Server and control the media streams resources in the MRFP accordingly
Generate CDRsBreakout Gateway Control Function (BGCF) select to which PSTN network a session should be forwarded Forward the session signaling to the appropriate MGCF and
BGCF in the destination PSTN network
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3.2.2 Mobile Station Addressing for Accessing the IMS
In order for a mobile user to use the services provided by a visited IMS, the mobile needs to have an IP address (i.e., the mobile’s PDP address) that is logically part of the IP addressing domain of the visited IMS.A PDP context will be activated for this address so that the packets addressed to this IP address can be forwarded by the 3GPP packet domain to the mobile.
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SGSN GGSN
VisitedNetwork’s
IMS
Visited Network PS Domain
PDP Context
Mobile’s IP addressrepresents the mobile’sattachment point to the visited IMS.
Mobile
Fig. 3.5 Mobile station addressing for accessing IMS services
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3.2.3 Reference Interfaces
Interfaces for SIP-based signaling and service control: Mg, Mi, Mj, Mk, Mr, Mw use SIP as the signaling protocol
Interfaces for controlling media gateways: Mc, Mp Use H.248 Gateway Control Protocol
Interfaces with the Information Servers: CxInterfaces with external networks: Mb, Mm, and Go IP-based protocols
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3.2.4 Service Architecture
A mobile’s home network provides service control for the mobile’s Home Subscribed Services even when the mobile is currently in a visited network.A mobile’s S-CSCF will always be a S-CSCF in the mobile’s home network.A service platform provides service control for real-time services.
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Visited Network Home Network
Home Network
(a) Service platform in mobile’s home network
(b) External service platform
Visited Network
P-CSCF
ApplicationServers
I-CSCF S-CSCF
P-CSCF I-CSCF S-CSCF
ApplicationServers
Mobile
Mobile
Fig. 3.6
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Service Platforms
Three standardized platforms SIP application server Open Service Access (OSA) Service Capability
Server (SCS) Gateway to OSA application server
IP Multimedia Service Switching Function (IM-SSF) Gateway to CAMEL Service Environment (CSE)
Same interface: IMS Service Control (ISC) use SIP
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IP Multimedia Subsystem
OSA API
ISCISCISC
Sh CxShCAP
MAP
OSA SCS (for Providing
Open Access to 3rd-Party Service Providers)
S-CSCF
IM-SSF(for Interface with
Legacy Service Platform)
CAMEL ServiceEnvironmentHSS
SIP Application Servers
OSAApplication Servers
Si
Fig. 3.7 Interactions between S-CSCF and service platforms
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3.2.5 Registration with the IMS
Local P-CSCF Discovery: discover the IP address of a local P-CSCF in the visited IMS obtain from the visited GGSN as part of the PDP
Context Activation process uses DHCP to discover after the PDP context is
activated
Registration with IMS: perform SIP registration with the visited IMS and the mobile’s home IMS
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DHCPServer
DNSMobile
1. PDP Context Activation
2. DHCP Query/Response
3. DNS Query and Response
SGSN GGSN
Fig. 3.8 3GPP Local P-CSCF discovery
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P-CSCF
HSS
S-CSCFI-CSCF
1. SIP Register 2. SIP Register 7. SIP Register
15. SIP 200 OK 14. SIP 200 OK 13. SIP 200 OK
3. Cx-Query
4. Cx-QueryResponse
8. Cx-Put 10. Cx-Pull
9. Cx-Put 11. Cx-PullResponse Response
Visited Network Mobile’s Home Network
Mobile
5. Cx-Select-pull
6. Cx-Select-pullResponse
12. Service
Control
Fig. 3.9 3GPP IP Multimedia Subsystem registration procedure
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3.2.6 Deregistration with the IMS
Mobile initiatedNetwork initiated initiated by registration timeout initiated by a network administrative
function such as HSS or S-CSCF
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P-CSCF
HSS
S-CSCFI-CSCF
1. SIP Register 2. SIP Register 5. SIP Register
11. SIP 200 OK 10. SIP 200 OK 9. SIP 200 OK
3. Cx-Query 4. Cx-QueryResponse
7. Cx-Put 8. Cx-Put Response
Visited Network Mobile’s Home Network
Mobile
6. Service
Control
Fig. 3.10 Mobile-initiated deregistration
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UE
P-CSCF S-CSCF HSS
1. Timer Expires
1. Timer Expires
2. Service Control
3. Cx-put
4. Cx-put-Resp
Fig. 3.11 Network-initiated deregistration by registration timeout
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UE
P-CSCF S-CSCF HSS
2. Service Control
7. Cx-Deregister Response
1. Cx-Deregister
3. Deregister4. UE Inform
6. 200 OK5. 200 OK
Fig. 3.12 Network-initiated deregistration by HSS
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UE
P-CSCF S-CSCF HSS
1. Service Control
6. Cx-Put
2. Deregister3. UE Inform
5. 200 OK4. 200 OK
7. Cx-Put response
Fig. 3.13 Network-initiated deregistration by S-CSCF
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3.2.7 End-to-End Signaling Flows for Session Control
Mobile origination flowMobile termination flowS-CSCF to S-CSCF signaling flow
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P-CSCF
S-CSCF S-CSCF
P-CSCF
2. S-CSCF to S-CSCF Flow
Originating Mobile’sHome Network
Destination Mobile’sHome Network
OriginatingMobile’s
Visited Network
DestinationMobile’s
Visited Network
1. M
obile
Orig
inat
ion
Flow
3. M
obile
Ter
min
atio
n Fl
ow
Originating Mobile Destination Mobile
Fig. 3.14 3GPP end-to-end session signaling flow
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Fig. 3.15Mobile origination flow
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Fig. 3.16S-CSCF to S-CSCF signaling flow
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Fig. 3.17Mobile termination flow
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Fig. 3.18 Release flow: mobile initiated
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3.3 3GPP2 IP MULTIMEDIA SUBSYSTEM (IMS)
3GPP2 IP Multimedia Domain (MMD): provide end-to-end IP connectivity, services, and features through the core network to subscribers Packet Data Subsystem (PDS): support
general packet data service IP Multimedia Subsystem (IMS): provide
multimedia session capabilities
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Fig. 3.193GPP2 MMD core network architecture
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Fig. 3.20 3GPP2 IMS architecture
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Fig. 3.21 3GPP2 IMS service platforms
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Fig. 3.223GPP2 IMS service control