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IP Multimedia SubsystemPart 1
Marek Ś[email protected]
Institute of Telecommunications
Project is co-financed by European Union within the European Social Fund1EIMS - 2016
Introduction
3
Evolution of telecomService Delivery Platforms (SDPs)
INAP, CAP, CAMEL, GSM
SIP, OSA/PARLAY, JAIN, UMTS
INSCP & CSE
Switching system software
3G, NGN, IMS
Intelligenceembedded in
software of switchingsystems
Intelligencein a separateservice node
Intelligenceof cooperating
components
PSTN, ISDN
IP TV, RCS, APIs(BONDI, REST, … )
4G, LTE, EPC, SDP
Converged &embedded
communications
EIMS - 2016
4
Evolution of service implementation model
Traditional closed model New open model
Physical transport
Call control and switching
Services and applications
Physical transport
Multimedia session control
Services & applications +management
API
API
Service interface
Network interface
Opening of the control infrastructure and service architecture using standard APIs - Parlay OSA/X APIs and JAIN APIs. Breaking of the classic value chain. Separation of service development, deployment and operation. VNO and MVNOmodels. EIMS - 2016
5
Change of model: „Spaghetti” →„Lasagna”
„Spaghetti” type architecture „Lasagna” type architecture
Pri
va
te n
etw
ork
s
Fix
ed
ne
two
rks
Mo
bil
e n
etw
ork
s
Common service capabilities
Transport and access
Application and content
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6
Convergence - a buzzword …
• Overloaded concept – many flavours of „convergence”
• Voice - data– Common transport network
• FMC– ETSI TISPAN NGN
• Terminal convergence– GSM/UMTS + WLAN
– Session continuity
– Single address (ENUM)
• Application convergence– Context and presence embedded in applicatiions
– Click-to-call
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7
Open source+
Web 2.0/3.0
Mobility VirtualizationNFV / SDN
Broadbandand/or wireless
access
Convergence
Securityand
privacy
CloudComputing
Presenceand
context
Multimedia
Convergence – key factors
Computer science and Internet – Content, media, networked IT services
Telecommunications – A mix of solutions, technical and legal aspects
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Areas of convergence
Convergence planes
NetworkServices andapplications
Terminals Charging Contents
Everybody can offer (almost) everything …
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9
Internet
TV
Mobile
Fixed
Internet
TV
Mobile
Fixed
Internet
TV
Mobile
Fixed
Internet
TV
Mobile
Fixed
Market liberalization (LLU, BSA, ...) + business models (MVNO/MVNE, networked IT services…) + resource sharing (fibers, lambdas, ducts, masts, servers, …)
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IP Multimedia (IM) Domain• Implementation of multimedia services
• Integration of PS and CS domains and services
UMTS RNS (UTRAN)
GSM BSS
PDN(IP)
PSTN
Core network
PS Domain
CS DomainME
Home
Domain
IM Domain - IMS
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IMS integrates services
Voice
SMS
Instant Messaging
MMS
Pre-IMS - „islands of services” IMS – integration of services and combinational services
Voice / Video
SMS
Instant Messaging
MMS
From separate usage of standalone services ... to integrated usage of services
based on presence
In groups – communities
PoC
TV
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IMS - requirements
• Support for:– establishing IP Multimedia sessions
– mechanism to negotiate Quality of Service
– interworking with the Internet and circuit-switched networks
– Roaming
– strong control imposed by the operator with respect to the services delivered to the end-user
– rapid service creation without requiring standardization (service capability standardization)
– access from networks other than GPRS
3GPP IP Multimedia Subsystem (1/2)
• IMS standardized by 3GPP as part of UMTS Release 5
– Basic VoIP, IM, Presence support on top of GPRS
– Adaptations to “real word” made in Release 6 (QoS, PoC support)
– Release 7 will look at unified IMS for all IP access networks (DSL, WLAN, etc.)
– Release 8 – Common IMS
• The IMS is based on the IP family of protocols:
– Adapted SIP (Session Initiation Protocol) for Session Control
– Diameter for AAA (Authentication, Authorization & Accounting)
– Others: SDP, RTP, RTCP, MGCP, etc.
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3GPP IP Multimedia Subsystem (2/2)
• Key components of the IMS architecture:
– Extended AAA Server - Home Subscriber System – as evolution of the HLR)
– SIP servers / softswitches
– Media Servers & Media Gateways
– Application Servers
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15
Standardization of NGN/3G and IMSwww.3gpp.org
2001 2002 2003 2004
ITU-T NGN FG
2005
OASIS, OMA
3GPP Release 4
3GPP Release 5
3GPP Release 6
TISPAN NGN R1
3GPP2 MMD
3GPP Release 7
2006 2007
3GPP Release 8
2009
Common IMS
2016
3GPP Release 9
3GPP Release 10-13
2010 …
3GPP Specifications
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Evolution of UMTS
• LTE (Long Term Evolution) - 4G wireless access technology from 3GPP
• IP based only access and high bandwidth requirements implied 3GPP study of a converged architecture to support it - System Architecture Evolution (SAE)
• The Evolved Packet Core (EPC) is the result of this study. – All-IP architecture to which LTE and other 3GPP (UMTS,GPRS) and non-3GPP (WiMAX,HRPD,WLAN
etc) access systems connect to.
– EPC provides a converged solution for Security, QoS , Mobility and connection to the IP based services (IMS or the Internet)
• Evolved Packet System (EPS) = EPC + LTE access network (E-UTRAN)
• IMS is on top of the EPC as one of the possible IP Services layer.
• Data interface (SGi) from the main gateway of the EPC (PDN-Gw) to IMS
• Signaling/control interface (Rx) from the application function (the P-CSCF in IMS) to the main session controller in charge of the authorization, admission control, resource reservation, QoS (PCRF)
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General IMS architecture
E-CSCF
P-CSCF
S-CSCF MGCF
HSS
Cx
IP Multimedia Networks
IMS-
MGW
CS Network
Mn
Mb
Mg
Mm
MRFP
Mb
Mr
Mb
Legacy mobile signalling Networks
I-CSCF
Mw
Mw
Gm
BGCF Mj Mi
BGCF
Mk Mk C, D,
Gc, Gr
UE
Mb
Mb
Mb
MRFC
SLF
Dx
Mp
CS
CS
Rx
Mm
LRF
Ml
Le
BGCF
Mi
LCS
Client
Cx
Dx
AS
Sh
Ut
Mw
ISC
IBCF Mx
Mx
Mx
Ma
Dh
TrGW Izi
Ici Ix
Mg
Source: 3GPP TS 23.002
EIMS - 2016 19
Main 3GPP IMS standards
• 22.228: IP multimedia subsystem; Stage 1• 23.207: End-to-end QoS Concepts and Architecture• 23.218: IP Multimedia (IM) session handling; IM call model• 23.228: IP Multimedia Subsystem (IMS); Stage 2• 24.228: Signalling flows for the IP multimedia call control based on SIP and SDP; Stage 3• 24.229: IP Multimedia Call Control Protocol based on SIP and SDP; Stage 3• 29.228: IP Multimedia (IM) Subsystem Cx Interface; Signalling flows and message contents• 29.229: Cx Interface based on the Diameter protocol; Protocol details• 29.328: IP Multimedia Subsystem (IMS) Sh Interface; Signalling flows and message contents• 29.329: Sh interface based on the Diameter protocol; Protocol details• 29.207: Policy Control over Go Interface• 29.208: End-to-end Quality of Service (QoS) signalling flows• 32.200: Telecommunications management; Charging management; Charging principles• 32.225: Telecommunications management; Charging management; Charging data
description for the IMS domain• 33.203: 3G security; Access security for IP-based services• 33.210: 3G security; Network Domain Security (NDS); IP network layer security
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From IETF SIP ….
Request
SIP Proxy server
IP/Internet
Response
DNSAS – SIP application server
SIP User Agent- UA
SIP User Agent- UA SIP User Agent- UA
SIP User Agent- UA
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… to 3GPP IMS SIP
P-CSCF
I-CSCFS-CSCF
Application server
DNS
SLF
DNS HSS
IP Core Network with QoSsupport
AS – SIP application serwer
SIP User Agent- UA
SIP User Agent- UA
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IMS in UMTS
CS Domain
PS Domain
“call”
“session”
IP core network
TDM, ATM or IP
MSC GMSC
SCP
IMS
HLR ???HSS
SGSN GGSN
MGW MGW
PSTN
Intranet/Internet
CSCF
MGCF “IP based”
GMSCServer
MSCServer
23Mobile
IP
Residential
Wi-Fi / WiMax wireless IMS access
PoC MessagingGLMS MultimediaTelephony
Licensed radio IMS
PresenceCSI
WLAN Access to IMS
VCC MultimediaTelephony
MultimediaTelephony
IMS standardization activities
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Protocols related to IMS services
• Instant messaging and presence
– SIP/PoC i 3G H.324M – Video Mail (VM)
– SIP – Multimedia Messaging (MMS)
– 3G-H.324M – Multimedia advertising
• Conversational multimedia services
– SIP/PoC – Push-To-Talk (PTT) over Cellular (PoC)
– SIP i 3G-H.324M – videotelephony and videoconferencing
• Video streaming
– SIP 3G-H.324M (based on DTMF video portals)
– RTSP (IP TV, monitoring)
• Multimedia games
– SIP/JSR-180 (J2ME)
– SIP/PoC
3GPP IMS architecture
25
control
transport
Visited network Home network
P-CSCF
HSS
S-CSCF BGCF MGCF
MGW
PSTN
H.248
SIPSIP SIP
SIP ISUP/IP
AS
Diameter
IP corenetwork
Accessnetwork
PCM
I-CSCF
Diameter
SIP
Diameter
HSS – Home Subscriber Server
CSCF – Call Session Control Function
BGCF – Breakout Gateway Control Function
MGCF – Media Gateway Control Function
VoIP – RTP – transport of media streams
Service plane
Control plane
Transport plane
SGW ISUP/MTP
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IMS layers: transport, session control, applications
Transport/user layer
Application layer
Control layer
S-CSCF
HSS
SIP AS SIP AS
MRFC
B-GW
SIP Diameter PSTN
RTP
I-CSCFP-CSCF
MRFP
H.248 / MEGACO
Parlay ASCAMEL
CSE
OSA GW IM SSF
Parlay API CAP API
ISC interface
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Three layer architecture of IMS (1/3)
• Unified architecture that supports a wide range of services enabled by the flexibility of Session Initiation Protocol (SIP)
• Transport and Endpoint Layer– Initiates and terminates SIP signaling to set up sessions and provide bearer
services such as conversion of voice from analog or digital formats to IP packets using Real time Transport Protocol (RTP)
– Provides the media gateways for converting the VoIP bearer streams to the PSTN TDM format.
– The media server provides many media related services including conferencing, playing announcements, collecting in-band signaling tones, speech recognition, speech synthesis, etc.
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Three layer architecture of IMS (2/3)
• Session Control Layer– Call Session Control Function (CSCF)
• provides the registration of the endpoints and routing of the SIP signaling messages to the appropriate application server
• interworks with the transport and endpoint layer to guarantee QoS across all services
– Home Subscriber Server (HSS) database• maintains the unique service profile for each end user
• By centralizing this information, applications can share information to create unified personal directories, multi client type presence information and blended services.
– Media Gateway Control Function (MGCF)• Interworks SIP signaling with the signaling used by the media gateway
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Three layer architecture of IMS (3/3)
• Application Server Layer
– Contains application servers, which provide the end-user service logic
• Telephony Application Server
• IP Multimedia – Services Switching Function (IM-SSF)
• Supplemental Telephony Application Servers
• Non Telephony Application Servers
• Open Service Access – Gateway (OSA-GW)
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30
IMS architecture
UE
P-CSCF I-CSCF S-CSCF
BGCF MGCF
HSS
Visited network Home network
AS
Gm
Mw
ISC
Mj
Mi
MRF
Cx
Sh
<SIP>
<DIAMETER>
<SIP>
<SIP>
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Terminal - User Equipment (UE)
• SIP UA
• Establishes GPRS PDP context for– signaling
– media transport
• ISIM for authentication– Public and Private User identity
– User Network address
– Security algorithms and keys
– At least USIM
• Corellation of session control with QoS reservation
EIMS - 201632
IMS components
UE
P-CSCF I-CSCF S-CSCF
BGCF MGCF
HSS
AS
Gm
Mw
ISC
Mj
Mi
MRF
Cx
Sh
<SIP>
<DIAMETER>
<SIP>
<SIP>
Home networkVisited network
EIMS - 2016 33
Proxy Call Session Control Function - P-CSCF
• P-CSCF (Proxy Call Session Control Function) – entry point of user terminal into the IMS world
– acting as an outbound/inbound SIP proxy server
– an IMS terminal communicates with a single P-CSCF during the registration
– establish IPsec security associations toward the IMS terminal
– verify the correctness of SIP request sent by the IMS terminal
– compressor and a decompressor of SIP messages
– may include PDF (Policy Decision Function) to authorize media plane
– generate charging information
EIMS - 201634
IMS components
UE
P-CSCF I-CSCF S-CSCF
BGCF MGCF
HSS
AS
Gm
Mw
ISC
Mj
Mi
MRF
Cx
Sh
<SIP>
<DIAMETER>
<SIP>
<SIP>
Visited network Home network
EIMS - 2016 35
Interrogating Call Session Control Function (I-CSCF)
• A SIP proxy located at the edge of an administrative domain
• The address of the I-CSCF is listed in the DNS records of the domain
• I-CSCF has an interface to the SLF and HSS and route the SIP request to the appropriate destination (typically S-CSCF)
EIMS - 2016
36
IMS components
UE
P-CSCF S-CSCF
BGCF MGCF
HSS
AS
Gm
Mw
ISC
Mj
Mi
MRF
Cx
Sh
Visited network Home network
I-CSCF
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Serving Call Session Control Function S-CSCF
• S-CSCF (Serving Call Session Control Function)
– Central node of the signaling plane
– Acts as a SIP server and a SIP registrar
•Maintains binding between the user location (e.g. IP address of the terminal) and the user’s SIP address of record (Public User Identity)
– Diameter interface to the HSS
•To download the authentication vectors of the user
•To download the user profile including service profile
•To inform the HSS of S-CSCF allocated to the user
– All the SIP signaling the IMS terminals sends and receives traverse the allocated S-CSCF
– Provides SIP routing (e.g. translation from phone number to SIP URI)
– Enforces the policy of the network operator
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IMS components
UE
P-CSCF I-CSCF S-CSCF
BGCF MGCF
HSS
AS
Gm
Mw
ISC
Mj
Mi
MRF
Cx
Sh
Visited network Home network
EIMS - 2016 39
Breakout Gateway Control Function (BGCF)
• Selects PSTN/CS domain to forward a call– local MGCF
– another BGCF
• MGCF selection process not defined– configuration
– TRIP or a similar solution
Media Gateway Control Function (MGCF)
• Gateway to PSTN
– SIP - PSTN mapping
– Establishes appropriate bearer capabilities
– Transcoding
– Acts as UA (registration not required)
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41
IMS components
UE
P-CSCF I-CSCF S-CSCF
BGCF MGCF
HSS
AS
Gm
Mw
ISC
Mj
Mi
MRF
Cx
Sh
Visited network Home network
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Media Resource Function (MRF)
• Supports conference services and announcements
• Multimedia Resource Control Function (MRFC)
– Interprets information from S-CSCF andAS
• e.g. conference reservation
– controls MRPF
• Multimedia Resource Processor Function (MRPF)
– Sets bearer capabilities based on MRFCrequests
– Mixing and distribution of media
– Media streaming for user interaction
• Uses H.248 (MEGACO)
MRFC
MRPF
SIP
H.248
Media
Interworking with PSTN – PSTN/CS Gateway
• PSTN/CS = MGCF + SGW + MGW
• MGCF (Media Gateway Control Function)
– ISUP-SIP mapping
– MGW control for media transcoding
– Selection of I-CSCF for calls to PSTN
• SGW (Signalling Gateway Function)
– Supports interworking between SS7 and MGCF
– Transport of ISUP messages in SIP messages to MGCF MGCF (SIP-T orBICC)
– ISUP/BICC/MTP – ISUP/BICC/SCTP/IP
• MGW (Media Gateway)
– Termination of media streams
• RTP - PCM
• AMR - G.711 EIMS - 2016 43
BGCF - Breakout Gateway Control Function
• SIP server – routing based on telephone numbering– Using of info delivered by TRIP protocol
• IMS – PSTN/PLMN calls
• Selection of an interworking network
• Selection of an appropriate PSTN/CS gateway (MGCF) ifinterworking refers to the same network in which BGCF islocated
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EIMS - 201645
Application Server (AS)• An SIP entity that hosts and executes
services
• Four modes of operation:
– AS acting as terminating UA, or redirect server
– AS acting as originating UA
– AS acting as a SIP proxy
– AS performing third party call control/ B2BUA mode
• ISC - SIP Interface to S-CSCF
• Implemetation variants of ASs– SIP AS
– OSA-SCS (Open Service Access-Service Capability Server)
– IM-SSF (IP Multimedia Service Switching Function)
S-CSCF
AS
ISC
1
2 3
4
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Implementation variants of IMS AS
CSCFS-CSCF
SIP Application ServerSIP AS
HSSHSSOSA service
capability server(SCS)
OSA servicecapability server
(SCS)
IM-SSFIM-SSF
Camel Service
Environment
CAMEL ServiceEnvironment
OSA
application OSA AS
ISC
Cx ISC
ISC
CAP
MAP
Parlay OSA API
SCIM
Sh
Si
MRFCMRFC
Mr
AS AS
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Parlay OSA application servers – third parties
Online &Offline
Charging (ECF, CCF)
Service Delivery Platform
(Application server) Parlay App 1
Service Platform Trigger PointsParlay API (MPCC, MMM, Presence, Charging ...
SIP Interface
HSS
S-CSCF
SPT
SPT Filtering criteria
ISC
SIP
SIP-Server
Sh =
Diameter
Cx =
DiameterRo + Rf =
Diameter
Diameter
Parlay X GWParlay App 2
Parlay App 3
Parlay X App 1Parlay X App 2
Other accessnetworks
Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)
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IMS components
UE
I-CSCF
BGCF MGCF
HSS
AS
Gm
Mw
ISC
Mj
Mi
MRF
Cx
Sh
Visited network Home network
I-CSCF S-CSCF
AS
MRFI-CSCF
AS
P-CSCF S-CSCF
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Home Subscription Server (HSS)
• HSS (Home Subscriber Server)– Technically, an evolution of the HLR– Central repository for user-related information
• location information• security information (authentication and authorization)• user profile information (the services that the user is
subscribed to)• S-CSCF allocated to the user
• SLF (Subscriber Location Function)– Simple database that maps users’ addresses to
HSSs
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HSS – Home Subscriber Server
I-CSCF S-CSCF
Mw
SLF
Dx Cx
HSS AS
Cx
SIP
SIPDiameter
Sh
ISC
Diameter
GPRSaccess
MAP
SIP
Mw
The first registration
UAR: User-Authorization-RequestUAA: User-Authorization-AnswerMAR: Multimedia-Authentication-RequestMAA: Multimedia-Authentication-AnswerSAR: Server-Assignment-RequestSAA: Server-Assignment-AnswerRAND: Random challengeAUTN: Network Authorization TokenCK: Ciphering KeyIK: Integrity Key
13. UAR
1. Register
Visited network Home network
P-CSCF
2. Register
UA I-CSCF HSS
3. UAR
4. UAA
S-CSCF
Selection of r S-CSCF
5. Register
6. MAR
10. 401 UnauthorisedRAND||AUTN
12. RegisterRES
7. MAARAND||AUTN||XRES||CK||IK
9. 401 UnauthorisedRAND||AUTN
11. RegisterRES
Authenticationvector selection
8. 401 UnauthorisedRAND||AUTN
14. UAA
15. RegisterRES
22. OK20. OKCK||IK
21. OKCK||IK
Authentication
18. SAR
19. SAA
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EIMS - 2016 52
Home Network of Mobile A Home network of Mobile B
HSS - A
I-CSCF - A S-CSCF - A
HSS - B
S-CSCF - B I-CSCF - B
P-CSCF - A
Network Visited by Mobile A Network Visited by Mobile B
P-CSCF - B
Mobile A Mobile B
Call Control
11
22
33
4 4
5 5
Example: registration
EIMS - 2016 53
Control
Bearer
Visited network
of callee
Home network of called userHome network of
calling user
Visited network of callerP-CSCF
HSS
S-CSCFSIP
SIP
Diameter
P-CSCF
AS
HSS
S-CSCF SIPAS
SIP
Diameter
I-CSCF
Diameter
DNS
Packet
CoreAccess Access
SIP INVITE1
1
Retrieving user’s profile2
2
3
3 Execution of a service scenario
Resolution of User B home network address and
INVITE forwarding
4
4
Identification of Registrar for user B and INVITE forwarding5
5
Retrieving user’s profile 6
6
7
7 Execution of a service scenario
INVITE forwarding to do User B 8
8
Ringing / Alerting10
10
SDP session negotiation /
Reservation of resources
9
9
RTP
Answer / call active11
11
IMS users session
Packet
Core
SIP UESIP UE
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Home Network of Mobile A Home network of Mobile B
HSS - A
I-CSCF - A S-CSCF - A
HSS - B
S-CSCF - B I-CSCF - B
P-CSCF - A
Network Visited by Mobile A Network Visited by Mobile B
P-CSCF - B
Mobile A Mobile B
Call Control
1
2
3
4
5
6
7
Example 2 – IMS mobile call
EIMS - 2016 55
Control
Bearer
Network vizited by the caller Home network of the caller
P-CSCF
HSS
S-CSCF
BGCFMGCF
MGW
H.248
SIP
SIP SIP
AS
BGCF
SIP
SIP
PSTN
ISUPDiameter
PacketCore
Access
SIP INVITE1
1
2 3
Selection of access to PSTN and selection of MGCF4
4
ISUP IAM7
75
Seizing of a link/trunk and determination of MGW capabilities5
PCM
SDP session negotiation / Reservation of resources6
6
RTP stream
Ringing / Alerting8
8 9
Answer / Connect9
IMS to PSTN call
Retrieving user’s profile 2
3 Execution of a service scenario
EIMS - 201656
P-CSCF - A
Network Visited by Mobile A
HSS - A
I-CSCF - A S-CSCF - A
BGCF - A
Home Network of Mobile A PSTN
MGW - B
MGCF - B
Mobile A
Gateway Control
User Profile
User Profile
1 2
3
4
5
Call to PSTN (CS domain)
EIMS - 2016 57
IMS Session Setup and Control
• Happens after user registration (and authentication!)
• Goals of IMS session setup– Capability and media negotiation (e.g. codecs, port numbers, addresses)
– Network resource reservation and the support of QoS preconditions
• Additional functions performed by the IMS during the IMS Session Setup:– Routing to the terminating IMS (= the IMS of the B-Party)
– Routing / Breakout to the PSTN / CS-Domain when the B-Party is not in the IMS, but in the PSTN / CS-Domain
– Service Control / Invocation of Application Servers to trigger the execution of Originating- and/or Terminating IMS Services
– Integrity/Confidentiality Protection of SIP Messages
– QoS/Media Authorization
– SIP Signaling Compression
EIMS - 2016 58
IMS Session Setup and Control 1/4
Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)
EIMS - 2016 59
IMS Session Setup and Control 2/4
Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)
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60
IMS Session Setup and Control 3/4
Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)
EIMS - 2016 61
IMS Session Setup and Control 4/4
Source: IMS Tutorial -T. Magedanz (TU Berlin / Fraunhofer FOKUS)
EIMS
Project is co-financed by European Union within European Social Fund62EIMS - 2016
