ip multimedia subsystem part 5
TRANSCRIPT
IP Multimedia SubsystemPart 5
Marek Ś[email protected]
Institute of Telecommunications
Project is co-financed by European Union within the European Social Fund 1
Identification in IMS
tel:+48 602 210799
tel:+48 22 8259820
Identities of the user
Public User Identities
Private User IdentityIMS subscriber
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tel:+48 602 210799
tel:+48 22 8259820
Identities of the user and user’s service profiles
Public User Identities
Private User IdentityIMS subscriber
Service Profile 1
Service Profile 2
User’s Profile related with Private User Identityand with a set of Public User Identities
User’s Profiles
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Identification in IMS
• A need for a unique identification
• Private and Public ids.
• Public User Identity
– More than one PUI (Public User Identity)
– SIP URI or TEL URI
sip:[email protected]; user=phone
tel:+48-22-8323546
– TEL URI required for IMS-PSTN calls
– At least one TEL URI and one SIP URI per user
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IMS User Identity (1/2)
• Each IMS User has at least one private and one or more public User Identities
• IMS Private User Identity:
– belongs to the IMS operator
– not used for routing of SIP messages
– uses the format defined in RFC 2486• Example: [email protected]“
– stored on the ISIM card (in the mobile phone) and in the HSS (in the IMS User Profile)
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IMS User Identity (2/2)
• IMS Public User Identity:
– public and may be subject to Number Portability
– used for routing of SIP messages
– may use the SIP-URI format defined in RFC 3261 and/or the TEL-URI format defined in RFC 2806
• Example SIP-URI: “sip:[email protected]“
• Example TEL-URI: “tel:+491231234567”
– At least one Public User Identity is stored on the ISIM card
– All Public User Identities are stored in the HSS
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Public Service Identities (PSI)
• Similar to public user identities, but allocated to services (ASs) rather than users
• Used to identify specific applications Servers (enablers), such as presence or group list servers
• Typically take the form of a SIP URI or TEL URI
– sip: [email protected], [email protected], [email protected]
– tel: +49-900-123-456
• PSIs are treated as PUIs, i.e. easy routing of SIP requests to ASs (as end user systems also called “service routing”)
• Public Service Identities are not authenticated
– i.e., there is no corresponding private user (service) identity
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SIM, USIM and ISIM in 3GPP
• UMTS terminals feature Universal IntegratedCircuit Card (UICC)
• Stores subscription information, authenticationkeys, address book, message store
• Without UICC – only emergency calls
• Logical applications:
– Subscriber Identity Module (SIM),
– Universal Subscriber Identity Module (USIM)
– IP Multimedia Service Identity Module (ISIM)
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ISIM
• UICC application – 3GPP TS 31.103
• Stores IMS data for– User authorization and authentication
– Terminal configuration
• ISIM might coexist with SIM and USIM
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ISIM
• Private User Identity– Only one
• Public User Identity– One or more SIP URIs assigned to a user
• Home Network Domain URI– SIP URI containing the name of the home domain
– Used for resolving home network address during registration procedure
– Only one home network domain
• Long term secret– Authorization and computing of CK and IK keys
– IMS terminal uses IK and CK respectively for security and ciphering of SIP messages to/from P-CSCF
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User’s profile in HSS
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Implementation of services
IMS Service Architecture
S-CSCF
IM SSF
HSS
CAMEL Service
Environment
OSA/Parlay Gateway
Service Logic
OSA Application
Server
ISC (SIP+)
ISC (SIP+)
ISC (SIP+)
CAP
MAP
OSA API
Cx
DIAMETER
S-CSCF Serving -Call Session Control Function
IM SSF IP Multi-media Service Switching Function
HSS Home Subscriber Store
ISC IMS Service Control Interface
Native SIP Services
Legacy IN Services
3rd Party Services
SIP AS
Servlet/CPL/API
All 3 types of AS behave as SIP AS on ISC interface
towards S-CSCFDIAMETER
DIAMETER
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IMS Service Architecture
• Networks may contain more than one AS• AS may be specialized to certain services• S-CSCF communicates with AS via the ISC SIP interface• AS can be located in the home network or in the third party networks• AS can either act as:
– originating UA– terminating UA – SIP proxy– SIP redirect server– B2BUA
• Functionality of proxy depends on situation, parameters and configuration as well as on application itself
• AS may or may not remain in signaling path
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IMS Service Architecture
• Can be an End-User Service that includes communication service logic & client software
• Can be a Service Enabler that can be called and shared by many end-user services
• Includes Software Development Kit (SDK) to allow Service Providers and developers to easily deploy new services
• Can interact with other AS to generate new composite services via Service Orchestration Framework
• Pure IMS Applications – the new presence based IMS services (e.g. push-to-talk, push-to-video, push-to-text)
• Hybrid applications bridging between traditional telecom and IMS domain
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IMS Service Architecture
• SIP based interface between the S-CSCF and the service platforms
• Supports subscription to event notifications between the AS and S-CSCF
• Transports presence related messages, according to the Presence Service Platform
• Allows the AS to be notified of the implicit registered Public User Identities, Registration State and UE capabilities and characteristics
• S-CSCF performs any filtering (based on information received from the HSS) for ISC interaction
• Shall be able to convey charging information
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Filter Criteria
• Filter Criteria
– determines the services (provide to each other)
– two types of filter criteria • initial filter criteria - iFC
• subsequent filter criteria - sFC
– only initial filter criteria are used
• When S-CSCF receives a first request, S-CSCF evaluates initial filter criteria (i.e. INVITE, OPTIONS)
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Filter Criteria(1/3)
• HSS stores all the data to a user (user profile)
• User profile contains Private User Identity
• User profile is applicable and one or more service profiles
• Service profiles contains one or more Public User Identities and zero or more filter criteria
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Filter Criteria(2/3)
• Determines the service that are applicable to the collection of Public User Identity listed
• Priority– be assessed, compared with the same service profile
– S-CSCF first choose filter criteria higher priority
– Priority is a unique number
• Trigger Points– to determine whether or not the SIP request will be forwarded to a particular
AS
– A collection of Service Point Triggers
– Example:
• (Method = INVITE) AND (Request-URI=sip:[email protected])
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Filter Criteria(3/3)
• Service Point Trigger allows to access the information stored in different fields of the SIP request
• If there is no Trigger Point, SIP request is forwarded to the AS
• After the Trigger Points, the initial filter criteria contains the AS SIP URI
• The Service Information field contains transparent data that the AS needs to process the request
• The user profile – XML format
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Structure of Initial Filter Criteria
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An Example of Service Execution
• A service provided to a particular user(sip:[email protected])
• Caller is listed in a black list (sip:[email protected])
• Sip:[email protected] contains Trigger Point
(method = INVITE) AND (P-Asserted-Identity = sip:[email protected]) AND (Session Case = Terminating)
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An example of a user profile (XML)
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An example of a service
S -CSCF
IMS home networkAS
I-CSCF
1. INVITE 2. INVITE
9. 200 OK10 . 200 OK
3.
I NV
ITE 4
.I N
VIT
E 8.
20
0O
K 7.
20
0O
K
RTP
MRFC
MRFP
Based on: G.Carillo, M.A.Garcia-Matin, The 3G IP Multimedia Subsystem (IMS), Wiley, 2008.
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Several ASs providing services
S -CSCF
AS 2
I-CSCF
1. INVITE 2. INVITE
19. 200 OK20. 200 OK
5.IN
VI T
E 6.I NV
I TE 16
. 200
OK 15. 200
OK
AS 1 AS 3
9. INVITE
P-CSCF
10. INVITE
12. 200 OK 11. 200 OK
IMS home network
Based on: G.Carillo, M.A.Garcia-Matin, The 3G IP Multimedia Subsystem (IMS), Wiley, 2008.
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Filter Criteria Triggering Example
S-CSCF
AS 2AS 1
Incoming SIP leg Outgoing SIP leg
INVITE Match Initial Filter CriteriaFilter Criteria X to AS1 SPT HeaderA priority 1Filter criteria Y to AS2 SPT HeaderB priority 2
INVITE header =A
1
2
3
4
5
6
SIP messagewith header=B
SIP messagepossibly modified
SIP messageforwarded by S-CSCF
1. User initiates a SIP session by sending a SIP INVITE with header=A to its S-CSCF
2. S-CSCF evaluates the SPTs and finds a match with the filter criteria X. S-CSCF forwards request to AS1.
3. AS1 performs service logic and sends the SIP request back to the S-CSCF with a service related modification, i.e. change header=A to header=B.
4. S-CSCF evaluates the SPTs and finds a match with the filter criteria Y. S-CSCF forwards the request to AS2.
5. AS2 performs service logic and sends SIP request back to the S-CSCF.
6. No more filter criteria, S-CSCF forwards this request to the next hop based on the route decision.
7. If in step 3, the header was not changed by AS1, then S-CSCF evaluates the SPTs and does not find a match and routes the request to the next hop.
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Models of AS operation
AS functional model
AS -ILCM
AS
S-CSCF
ISC
AS -OLCM
Application LogicSh /SiHSS
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AS - terminating UA or Redirect server
S -CSCFSIP dialog #1
SIP dialog #1
From: XTo: YCall -ID: Z
From: XTo: YCall -ID: Z
AS
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AS as initiating UA
S -CSCF SIP dialog #1
SIP dialog #1
From: XTo: YCall -ID: Z
From: XTo: YCall -ID: Z
AS
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AS acting in the SIP proxy mode
S -CSCF SIP dialog #1
SIP dialog #1
From: XTo: YCall -ID: Z
From: XTo: YCall -ID: Z
SIP dialog #1From: X
To: YCall -ID: Z
SIP dialog #1
From: XTo: YCall -ID: Z
AS
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AS acting in the 3PCC / B2BUA mode
S -CSCF
AS
SIP dialog #2
SIP dialog #2
From: PTo: QCall -ID: R
From: PTo: QCall -ID: R
SIP dialog #1From: X
To: YCall -ID: Z
SIP dialog #1
From: XTo: YCall -ID: Z
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AS „call” model
AS-ILCM
AS-OLCM
AS-Logic
ASSIP request
SIP answer
SIP request
SIP answer
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Termination of a session by AS
AS-ILCM
AS-OLCM
AS-Logic
SIP BYESIP 200 OK
AS
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Session termination request forwarded by AS
AS-ILCM
AS-OLCM
AS-Logic
SIP BYE
SIP BYE
From: ATo: BCall-ID:YCseq:Z
From: ATo: BCall-ID:YCseq:Z
AS
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Session termination request initiated by AS
AS-ILCM
AS-OLCM
AS-Logic
SIP BYEFrom: CTo: DCall-ID:WCseq:X
SIP BYEFrom: ATo: BCall-ID:YCseq:Z
AS
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IMS - delivery of services - wrap up
• S-CSCF determines that a call requires enhanced service processing
– Filtering may be based on:• calling / called party
• other mechanism defined by filtering criteria eg. SIP message type, header fields, etc.
• Based on FC, the S-CSCF determines the address of the AS and relays the call to the AS function. The AS receives the call and invokes the appropriate service logic taking one of the following actions:
– Redirects the call to a new destination
– Send the call back through the S-CSCF in order to monitor subsequent callevents (ie. act as a SIP Proxy)
• The AS, based on some other input, can also set-up calls between other entities in the network
– i.e. act as a B2BUA
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IMS service platform interfaces
Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)
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EIMS
Project is co-financed by European Union within European Social Fund 40