IMS Services Sebastian Schumann Slovak Telekom

17. April 2013 Bratislava, Slovakia

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

Outline ¡ IMS and its Services

¡ Service Triggering

¡ Sample Services

¡ Other Aspects

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…

IMS and its Services

IMS: End User Perspective

Voice/video

SMS/MMS

Instantmessaging

Mail

Voice/Video/IMConferencing/App sharing/MM chat/

Others

content contentShared content

Today services Integrated „all-IP“ services

Technology Trends

Services D

ata/

IP N

etw

orks

Mob

ile N

etw

orks

PSTN

/ISD

N

CAT

V

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 architecture

Single/simple/cost-effective network infrastructure for existing & new services

IMS: Simplified Concept

Access & Transport Plane

Core Network Session

Control Plane

Service Architecture Applications/Services

Plane

HSS CSCF

Access Network

Other Networks

Web Portal

Application Servers

Session Control

Centralized Databases

Media Control & Gateways

Media Server

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

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

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)

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

Databases ¡ HSS ¡ Data storage for all subscriber and service-related data

¡ SLF ¡ Find HSS address for multiple HSS environment

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)

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)

Service Triggering

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)

Service Profile

Service Profile ctd.

Triggering

Triggering ctd.

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

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

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)

Sample Services

Services.

http://www.flickr.com/photos/soutra/430186540/

http://gsmworld.com/images/rcs/img_gallery/eyeP-eComRCS-Windows.3.png

http://www.flickr.com/photos/jre/3263704032/

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)

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)

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

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

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“

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)

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

MwMi

ISC

GmMb

Mb

Ici

Izi

Mx

SIP

DNSMedia

Mw

Ma

I-CSCF

HSS

Cx

Cx

Diameter

HTTP

Sh

Mb

Mx

RCS-e flow diagrams

Figure 1: RCS-e alternative configuration: Initial request

RCS-e flow diagrams ctd.

Figure 1: RCS-e capability discovery

RCS-e flow diagrams ctd.

RCS-e service Tag IM/Chat +g.3gpp.iari-ref="urn%3Aurn-7%3A3gpp-application.ims.iari.rcse.im" 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

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

Protocols

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

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 atlanta.example.com

m=message 7654 TCP/MSRP *

a=accept-types:text/plain

a=path:msrp://atlanta.example.com:7654/jshA7weztas;tcp

MSRP ctd. ¡  MSRP exchange MSRP a786hjs2 SEND To-Path: msrp://biloxi.example.com:12763/kjhd37s2s20w2a;tcp From-Path: msrp://atlanta.example.com:7654/jshA7weztas;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://atlanta.example.com:7654/jshA7weztas;tcp From-Path: msrp://biloxi.example.com:12763/kjhd37s2s20w2a;tcp -------a786hjs2$

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)

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

Messaging/Presence ¡ SIP MESSAGE

¡ SIP SIMPLE ¡ SIP SUBSCRIBE/NOTIFY

¡ SIP PUBLISH

¡ Many extensions

¡ Standard bodies: IETF, OMA

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

SUBS

CR

IBE

200

OK

200

OK

NO

TIFY

UE

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)

¡ 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.

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

Other Aspects

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

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

Q/A

Your Questions!

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?

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)

Sebastian Schumann mail@s-schumann.com @s_schumann sschumann

Thank you!

Download ¡ This lecture is available at http://bit.ly/fiit-ims-services

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.