IMS Signaling

Transcript

1. IMS Signaling Sebastian Schumann schumann@ktl.elf.stuba.sk http://www.ngnlab.eu
2. Outline • Recapitulation • IMS Registration • IMS Session Establishment • IMS Application Layer – Interaction with IMS core – Interaction with User Equipment (UE) The slides only summarize the lecture. Take notes!
3. Recapitulation • IMS is an open architecture for mobile and fixed services • The core and its services are independent from the access • Layered architecture – Transport, session control, applications – Transparency through standard interfaces • Session Control Layer – End point registration – Session establishment • Application Layer – Service Logic
4. Recapitulation ctd. • Service Control Layer – SIP: P/I/S-CSCF – DIAMETER: HSS • Application Server – SIP/DIAMETER interface towards service control layer – XCAP interface (based on HTTP) towards UE – Call related application logic – IMS service (e.g., Presence, PoC) – Service Creation Environment
5. IMS Registration • Required before a user can access services • Precondition: UE has IP address and knows IMS entry point • All CSCF are used – P-CSCF (home/visited): Entry point, determines I-CSCF – I-CSCF (home): Determines S-CSCF – S-CSCF (home): Authenticates the subscriber, registers IMS subscriber, interacts with service layer • User assigned to one S-CSCF after successful registration – Knows user profile until de-registration
6. User Identities • User identities – Private User Identity (user@realm) • Authentication and Subscription identification • Not used for routing – Public User Identity (sip:user@domain.tld or tel:+1234567890) • Contact to be reached by others • SIP URI or tel URL • Implicit Set of public user identities for grouping registration • Services and other network entities can be addressed using a SIP URI • User identities are part of the user profile
7. Relations between Identities IMS Subscriber Private UID 2 Private UID 1 Public UID 1 Public UID 3 Public UID 2 Public UID n . . . } Implicit Set
8. Registration call flow P-CSCF I-CSCF S-CSCF HSS UE SIP DIAMETER Please see “IMS overview” from Eugen Mikoczy for details. Take notes to understand the components and process. Whiteboard: Message exchange
9. IMS Session Establishment • After registration, subscriber is reachable through public user identity for communication • IMS subscriber can access services now or perform calls • P-CSCF (home or local) – Proxy, contacts assigned S-CSCF for the calling subscriber • S-CSCF (home) – Service control and logic – Contacts application or other party • I-CSCF – Entry point for communication from other domain
10. Session establishment outgoing (simplified) P-CSCF I-CSCF S-CSCF DNS UE Please see “IMS overview” from Eugen Mikoczy for details. Take notes to understand the components and process.
11. Session establishment incoming (simplified) P-CSCF I-CSCF S-CSCF HSS UE
12. Application layer interaction • User profile contains also service profile • Service Profile – Public Identification (assigned subscribers) – Initial Filter Criteria (triggering AS interaction) • Initial Filter Criteria (iFC) – Trigger points with service point triggers (conditions when to interact) – Application server (SIP URI for interaction)
13. Service Profile User Profile Service Profile Includes information about service access and dependencies to user registration state and service availibility. Each service profile can be specified for a single user or shared by different users by linking the service profile.
14. Service Profile ctd. User Profile Indicator: registered/unregistered/independend The Indicator describe the dependency to user registration state. Three different states will be differ: - registered (user is registered) - unregistered (user is not registered) - independend (user registered or not)
15. Triggering User Profile Filter: Filter describe an term including information about trigger point and application server access data belong the service profile. An trigger point is a logical expression including sip message parts and matching expressionsaccording the service.
16. Triggering ctd. User Profile available if AS isn't Proceedings SIP-URI Logical expression: CNF: ( A or B ) and C DNF: ( A and B ) or C Filter: Trigger Point + AS Information Service Profile Indicator: registered/unregistered/independend Requested URI Method header Session case SDP line matches/ equals/ is one of Service Point Trigger:
17. Filtering • Only initial SIP requests • Initial filter criteria (iFC) retrieved from HSS during registration • Subsequent filter criteria (sFC) provided by application server (beyond 3GPP R8) – Allow dynamic definition of trigger points during application runtime
18. Example: Presence call flow • Service profile – assigned to users that want to use presence • IFC – AS: Presence Server – TP: CNF (&) • Method – PUBLISH – SUBSCRIBE • Event – Header: Event – Content: .*presence.* P-CSCF Presence Server S-CSCF SUBSCRIBE 200 OK 200 OK NOTIFY SUBSCRIBE 200 OK 200 OK NOTIFY SUBSCRIBE 200 OK 200 OK NOTIFY UE
19. Questions?
20. Now, I want answers  • Alice from IMS behind atlanta.com wants to subscribe to Bob from IMS behind biloxy.com • Alice is currently in Chicago, Bob is at home – Is it possible? – Where does Bob have to publish? – Where does Alice have to subscribe? – Which components are involved? – How is the call flow?
21. Summary – what I tried to achieve • Deepen understanding of CSCF/HSS roles – Function of components – Routing within control layer and towards applications • Understanding IMS user identities • Service control, routing, application layer interaction • Many things omitted in this presentation – Network access layer – S-CSCF assignments in detail, SLF/HSS separation – QoS resource reservation – PSTN Breakout – Charging
22. Backup
23. eXtensible Configuration Access Protocol • XCAP allows clients to read, write and modify data stored in XML format on server – Hard state presence information – Watcher authorization – Resource Lists • XML document sub-trees and element attributes are mapped into HTTP URIs  direct access via XPath • Various selections (e.g., one or more elements, children, attributes, content)
24. • Client/Server architecture like HTTP • Application Usage for certain application needs • HTTP primitives ‘Get’, ‘Put’ and ‘Delete’ are used • Body contains XML data to be added/modified eXtensible Configuration Access Protocol
25. Message flow • Interface exposed by XML Document Management Server • XDMS is located on application layer • Direct communication between UE and XDMS • Use cases – Store resource list – Authorize buddies XDMS UE XCAP
26. Domain Name Service • Link IP addresses with domain names • Support in locating SIP servers – NAPTR lookup – SRV lookup – A/AAAA lookup • NAPTR resolves the preferred protocol and the DNS string to locate the service – ngnlab.eu. 7200 IN NAPTR 10 50 "s“ "SIP+D2T“ _sip._udp.ngnlab.eu. • SRV look-up for a NAPTR given address indicates the domain and port the service listens on – _sip._udp.ngnlab.eu. 7200 IN SRV 0 0 5060 icscf.ngnlab.eu. • A/AAAA to find the IP address of the domain name – icscf.ngnlab.eu. 7200 IN A 147.175.103.213