ip multimedia subsystem part 5

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IP Multimedia SubsystemPart 5

Marek Średniawamareks@tele.pw.edu.pl

Institute of Telecommunications

Project is co-financed by European Union within the European Social Fund 1

Identification in IMS

sip:ms@pw.com

tel:+48 602 210799

ms@mobile.com

tel:+48 22 8259820

sip:marek@mydomain.com

Identities of the user

Public User Identities

Private User IdentityIMS subscriber

3

sip:ms@pw.com

tel:+48 602 210799

ms@mobile.com

tel:+48 22 8259820

sip:marek@mydomain.com

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

4

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:+48-8323546@telekom.pl; user=phone

tel:+48-22-8323546

– TEL URI required for IMS-PSTN calls

– At least one TEL URI and one SIP URI per user

5

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: user-X@ims.operator.com“

– stored on the ISIM card (in the mobile phone) and in the HSS (in the IMS User Profile)

6

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:user-X@company-X.com“

• 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

7

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: songdownload@t-online.de, presence@t-online.de, chat@partner.de

– 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

8

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)

9

ISIM

• UICC application – 3GPP TS 31.103

• Stores IMS data for– User authorization and authentication

– Terminal configuration

• ISIM might coexist with SIM and USIM

10

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

11

User’s profile in HSS

12

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

14

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

15

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

16

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

17

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)

18

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

19

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:user@example.com)

20

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

21

Structure of Initial Filter Criteria

22

An Example of Service Execution

• A service provided to a particular user(sip:goodguy@example.com)

• Caller is listed in a black list (sip:badguy@example.com)

• Sip:goodguy@example.com contains Trigger Point

(method = INVITE) AND (P-Asserted-Identity = sip:badguy@example.com) AND (Session Case = Terminating)

23

An example of a user profile (XML)

24

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.

25

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.

26

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.

27

Models of AS operation

AS functional model

AS -ILCM

AS

S-CSCF

ISC

AS -OLCM

Application LogicSh /SiHSS

29

AS - terminating UA or Redirect server

S -CSCFSIP dialog #1

SIP dialog #1

From: XTo: YCall -ID: Z

From: XTo: YCall -ID: Z

AS

30

AS as initiating UA

S -CSCF SIP dialog #1

SIP dialog #1

From: XTo: YCall -ID: Z

From: XTo: YCall -ID: Z

AS

31

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

32

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

33

AS „call” model

AS-ILCM

AS-OLCM

AS-Logic

ASSIP request

SIP answer

SIP request

SIP answer

34

Termination of a session by AS

AS-ILCM

AS-OLCM

AS-Logic

SIP BYESIP 200 OK

AS

35

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

36

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

37

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

38

IMS service platform interfaces

Source: T. Magedanz (TU Berlin / Fraunhofer FOKUS)

39

EIMS

Project is co-financed by European Union within European Social Fund 40

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