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IMS Services


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Lecture notes about IMS services. This lecture has been presented in 2013 in Bratislava, Slovakia at the Slovak University of Technology.

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IMS Services

  1. 1. IMS Services Sebastian Schumann Slovak Telekom 17. April 2013 Bratislava, Slovakia
  2. 2. About me ¡ Studied 2003 – 2007 telecommunications and computer sciences in Leipzig, Germany ¡ In Slovakia since 2006 ¡ Working for Slovak Telekom since 2007 ¡ Post-grad studies at Slovak University of Technology since 2007 ¡ Worked and implemented SIP and IMS software as well as carrier platforms
  3. 3. Outline ¡ IMS and its Services ¡ Service Triggering ¡ Sample Services ¡ Other Aspects
  4. 4. Note! ¡ These slides only summarize the lecture. Take notes. ¡ Fixed agenda: Understand IMS services ¡ Besides that: ¡  Ask questions (how is it done in real-world, how did Slovak Telekom do that) ¡  Interrupt (I don’t understand, can you provide samples, can we skip that) ¡  Contribute (I’ve heard/read that…, I’m interested in…) ¡  Discuss…
  5. 5. IMS and its Services
  6. 6. IMS: End User Perspective Voice/video SMS/MMS Instant messaging Mail Voice/Video/IM Conferencing/App sharing/MM chat/ Others content content Shared content Today services Integrated „all-IP“ services
  7. 7. Technology Trends Services Data/IPNetworks MobileNetworks PSTN/ISDN CATV Access Transport & Switching Networks Wireless Access Wireline Access IP Backbone Existing and newly emerging services Service & Network Control (QoS, Security, IP Mobility) Too costly, per-service network archit ecture Single/simple/cost-effective network infr astructure for existing & new services
  8. 8. IMS: Simplified Concept Access & Transport Plane Core Network Session Control Plane Service Architecture Applications/Services Plane HSSCSCF Access Network Other Networks Web Portal Application Servers Session Control Centralized Databases Media Control & Gateways Media Server
  9. 9. 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, authentication ¡  Session establishment, routing, interconnect ¡ Application Layer ¡  Service Logic
  10. 10. Recapitulation ctd. ¡ Service Control Layer ¡ SIP: P/I/S-CSCF, (BGCF, I-BCF, MRFC, AS) ¡ DIAMETER: HSS, (RACS/NASS, PCRF) ¡ Application Layer ¡ SIP/DIAMETER interface towards service control layer ¡ SIP/XCAP interface (based on HTTP) towards UE ¡ Call related application logic ¡ IMS service (e.g. Presence, PoC) ¡ Service Creation Environment ¡ Northbound integration through service APIs
  11. 11. IMS entities (Wiley, The IMS Concepts and Services) ¡ Session management and routing family (CSCFs) ¡ Databases (HSS, SLF) ¡ Services (e.g. AS) ¡ Support functions (PDF, SEG, THIG) ¡ Charging ¡ Interworking functions (BGCF, MGCF, IMS-MGW, SGW)
  12. 12. Session management & routing ¡ Proxy-CSCF – User contact point with the IM CN ¡ SIP compression, IPSec association, PDF interaction ¡ Interrogating-CSCF – Subscriber contact point ¡ Next-hop lookup from HSS, S-CSCF assignment and routing, THIG functionality ¡ Serving-CSCF – Service profile internal procedures ¡ Handling registration, challenging UE, routing decisions ¡ Responsible for Registration and Session Establishment, Charging Data Generation, Media content check
  13. 13. Databases ¡ HSS ¡ Data storage for all subscriber and service-related data ¡ SLF ¡ Find HSS address for multiple HSS environment
  14. 14. Application Server ¡ SIP Application Server ¡ Stand-alone AS ¡ Northbound integration using various protocols possible, e.g., HTTP REST, Parlay X ¡ Open Service Access (OSA) gateway ¡ Connect northbound to OSA Parlay based AS ¡ IM Service Switching Function (SSF) ¡ Connect northbound the AS layer to legacy services using IN protocols (e.g. INAP, CAMEL)
  15. 15. Protocols (extract) ¡ Signaling ¡  SIP (signaling protocol) ¡  SDP (embedded in SIP, describes the session, negotiation) ¡ Media ¡  RTP (end-to-end media delivery (audio, video)) ¡  MSRP (messaging, file transfer) ¡ DNS ¡ Diameter (AAA) ¡ IPSec (secure communication) ¡ MEGACO (media gateway control)
  16. 16. Service Triggering
  17. 17. Application layer interaction ¡ User profile contains 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)
  18. 18. Service Profile
  19. 19. Service Profile ctd.
  20. 20. Triggering
  21. 21. Triggering ctd.
  22. 22. 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) ¡ Allows dynamic definition of trigger points during application runtime
  23. 23. Application Routing ¡ I/S-CSCF are interaction points with the service layer ¡ I-CSCF for public service identities (PSI) à explicit access ¡ S-CSCF for services (of served users) à implicit access ¡ Applications have interface towards HSS ¡ User profile information ¡ Location information, service information ¡ Complexity of security, authorization, access interaction etc. all handled by the core
  24. 24. Application Routing ctd. ¡ Application server (AS) can have different functions ¡ Terminating AS (e.g., acting as user agent) ¡ Originating AS (e.g., wake up service, click to dial) ¡ SIP Proxy server (e.g., for SIP header manipulation) ¡ Back-to-back user agent (e.g., for deeper modifications in SIP dialog as supplementary service enabler)
  25. 25. Sample Services
  26. 26. Services. 430186540/ Windows.3.png
  27. 27. IMS Services ¡ Service that are often referred to ¡ IP Messaging (page-mode, session-mode) ¡ Push-to-talk over Cellular (PoC) ¡ Conferencing ¡ Presence ¡ Commercially deployed ¡ Voice (MMTel, VoLTE) ¡ RCS-e/RCS 5 (Joyn) ¡ Voice Call Continuity (VCC)
  28. 28. Rich Communication Suite Definition ¡  "Standard" definition ¡  End-to-end approach to define a clear set of available communication services that are interoperable ¡  Stakeholders in RCS are all key players in the telecom market (operators, vendors) ¡  Develop concrete value propositions for different stakeholders in the ecosystem ¡  Initial focus was on enriched mobile communication services, now RCS is extending the same services to the fixed environment ¡  Collaborative effort to facilitate the introduction of commercial IMS based rich communication services over mobile and fixed networks ¡  Several releases available (Rel. 1-5, RCS-e aka Joyn) ¡  Focus on residential user segment ¡  Not “defined”, but PBX integration/support not defined ¡  Focus NOT on end device applications (iPhone, Android)
  29. 29. RCS Services + use cases ¡ EAB enabled services ¡  Share presence + manage presence rules ¡  Capability exchange ¡ Video call, video sharing (inside/outside of call) ¡ Image sharing, whiteboard-feature ¡ File transfer ¡ Messaging ¡  multi-party, multi-device chat ¡  x-domain ¡ Provider interworking
  30. 30. Rich Communication Suite Releases ¡  Suite of rich communication services that can be launched from a capability enhanced address book (EAB) à EAB enriched call and enhanced messaging ¡  Rel. 1 ¡  EAB with capability exchange enables content sharing during a call and enhanced messaging (conversational view, chat). Backup/restore in network ¡  Mobile users only, direct relation with mobile operator ¡  Rel. 2 ¡  Introduction of broadband access, multiple clients, mobile phone required ¡  Network address book (NAB) allows synchronization (sharing btw. devices possible) ¡  Rel. 3 ¡  Enhanced services (presence states, messaging, network value added services) ¡  Content sharing outside voice call ¡  Single broadband access possible (w/o mobile phone) ¡  Rel. 4 ¡  LTE and fixed access enhancements, service enhancements ¡  Rel. 5 ¡  IP voice/video call, location sharing, service improvements
  31. 31. RCS-e/Joyn ¡ RCS-e (“e” for enhanced) is a simple and interoperable evolution to voice and text, which enables customers to send instant messages, video chat and exchange files in real time. All functions are built into the address book of mobile devices and based on the IMS. ¡ Enhanced Rel. 2 for faster time-to-market ¡ Powered by the five leading European mobile operators, incl. Deutsche Telekom ¡ Focused communication services (core services only) ¡  IM/Chat, file transfer, image/video share ¡  Social presence/profile information not mandatory ¡ Standard: “RCS-e provides a simple interoperable extension to voice and text today“
  32. 32. RCS-e 1.2.2 ¡  Dynamic capability discovery (SIP OPTIONS) ¡  Text messaging (as in RCS R2) ¡  One-to-one chat ¡  Group chat ¡  Add. Features to Rel. 2 ¡  Store &forward for chat ¡  Typing/delivery notify ¡  File Transfer (as in RCS R2) ¡  Image/Video Share during CS phone call (as in RCS R2)
  33. 33. Real sample architecture Mw I-SBCA-SBC RCS-e AS UE P-CSCF S-CSCF BGCF IBCF I-BGF RCS-e AS (Service) RCS-e AS (Config) ENUM A-BGF IPX Other MNO Mw Mi ISC Gm Mb Mb Ici Izi Mx SIP DNS Media Mw Ma I-CSCF HSS Cx Cx Diameter HTTP Sh Mb Mx
  34. 34. RCS-e flow diagrams Figure 1: RCS-e alternative configuration: Initial request
  35. 35. RCS-e flow diagrams ctd. Figure 1: RCS-e capability discovery
  36. 36. RCS-e flow diagrams ctd. RCS-e service Tag IM/Chat +g.3gpp.iari-ref="" File transfer +g.3gpp.iari-ref="urn%3Aurn-7%3A3gpp-application.ims.iari.rcse.ft" Image share +g.3gpp.iari-ref="urn%3Aurn-7%3A3gpp-application.ims.iari.gsma-is" Video share +g.3gpp.cs-voice Social presence information +g.3gpp.iari-ref="urn%3Aurn-7%3A3gpp-application.ims.iari.rcse.sp" Capability discovery via presence +g.3gpp.iari-ref="urn%3Aurn-7%3A3gpp-application.ims.iari.rcse.dp" Table 1: Complete SIP OPTIONS tag proposal for RCS-e
  37. 37. RCS-e flow diagrams ctd. ¡ SIP INVITE with ICSI/SDP for session establishment ¡ SIP MESSAGE for notifications ¡ MSRP for one-to-one/group chat and file transfer ¡ RTP for video share ¡ AS functions (samples) ¡ Group chat ¡ Aggregation ¡ Accounting, policy
  38. 38. Protocols
  39. 39. SIP ¡  SIP in the IMS has been already covered in the past ¡  Relevant main SIP headers for the service interaction ¡  P-Asserted-Identity (inserted by P-CSCF) trusted header indicating registered user’s IMPU ¡  Contact header contains ICSI ¡  SDP used for session description & codec negotiation ¡  Sample RCS-e ¡  OPTIONS discovery ¡  MESSAGE page-mode messaging & notifications ¡  INVITE session-mode messaging & notifications, file transfer, video share
  40. 40. Message Session Relay Protocol (MSRP) ¡ Message content within a SIP session (similar to RTP) ¡ Rendezvous mechanism mandatory (e.g. SDP) ¡ MSRP URI’s ¡ Accepted content ¡ SDP c=IN IP4 m=message 7654 TCP/MSRP * a=accept-types:text/plain a=path:msrp://;tcp
  41. 41. MSRP ctd. ¡  MSRP exchange MSRP a786hjs2 SEND To-Path: msrp://;tcp From-Path: msrp://;tcp Message-ID: 87652491 Byte-Range: 1-25/25 Content-Type: text/plain Hey Bob, are you there? -------a786hjs2$ MSRP a786hjs2 200 OK To-Path: msrp://;tcp From-Path: msrp://;tcp -------a786hjs2$
  42. 42. MSRP ctd. ¡ Key concepts ¡ Framing/message chunking (+ vs $) ¡ MSRP Addressing (URIs for send/recv, lists for relays) ¡ Scheme: msrp/msrps for TLS. TCP transport. ¡ Methods (e.g. SEND) and response codes (e.g. 200 OK) ¡ MSRP relays in the path ¡ More in RFC 4975 (protocol), RFC 4976 (relays)
  43. 43. 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 ¡ 7200 IN NAPTR 10 50 "s“ "SIP+D2T“ ¡ SRV look-up for a NAPTR given address indicates the domain and port the service listens on ¡ 7200 IN SRV 0 0 5060 ¡ A/AAAA to find the IP address of the domain name ¡ 7200 IN A
  44. 44. Messaging/Presence ¡ SIP MESSAGE ¡ SIP SIMPLE ¡ SIP SUBSCRIBE/NOTIFY ¡ SIP PUBLISH ¡ Many extensions ¡ Standard bodies: IETF, OMA
  45. 45. Example: Presence call flow ¡  Service profile ¡  assigned to users that want to use presence ¡  IFC ¡  AS: Presence Server ¡  TP: CNF (&) ¡  Method and ¡  PUBLISH or ¡  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 200OK 200OK NOTIFY UE
  46. 46. eXtensible Configuration Access Protocol (XCAP) ¡ 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 à direct access via XPath ¡ Various selections (e.g., one or more elements, children, attributes, content)
  47. 47. ¡ 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 XCAP ctd.
  48. 48. 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
  49. 49. Other Aspects
  50. 50. Northbound Interface – API ¡ Not standardized/partially standardized integration point with other applications/enablers or with non- IMS clients ¡ Various protocols possible ¡ XCAP ¡ Parlay X ¡ HTTP REST ¡ Standardization approaches exist, e.g., GSMA OneAPI, RCS-e API
  51. 51. Service Orchestration ¡ Querying multiple services ¡ Services querying other services ¡ Compilation of services by using various enablers ¡ Standardization approaches (e.g. SCIM) ¡ Approach ¡ SIP AS towards the IMS using ISC ¡ Connecting to multiple AS via ISC, optionally also to other AS w/ different protocols
  52. 52. Q/A Your Questions!
  53. 53. Is anything still unanswered? ¡  How do IMS services work? ¡  Why is the IMS needed for some communications services? Is it? ¡  But I have heard of service X, why don’t they use the IMS? ¡  Will we build all future services on top of IMS? ¡  Are IMS services only those inherited from the Telco past? ¡  Will Telco’s deploy multiple IMS? IMS in the cloud? Share an IMS? ¡  Will IMS bring in new revenues? Is it cheaper to deploy services on the IMS compared to stand-alone deployments?
  54. 54. Summary ¡ Quick IMS recapitulation ¡ Focus on service layer ¡ Interaction with the IMS ¡ Sample services, incl. protocols and principles ¡ Other means of integrating IMS services /with IMS services ¡ Hopefully covered all open questions (last chance J)
  55. 55. Sebastian Schumann @s_schumann sschumann Thank you!
  56. 56. Download ¡ This lecture is available at
  57. 57. References 1.  Standards 2.  RCS-e related pictures from GSMA RCS-e 1.2.2 Spec If you feel content where you hold the copyright is displayed within these slides and you do not like it, miss a link/reference, or want me to remove it altogether please let me know. Thanks to Eugen Mikoczy and Stephan Massner for contributing to the slides.