IP MULTIMEDIA SUBSYSTEMS IMS

Introduction

The IP Multimedia Subsystem (IMS) is an architectural framework based on a series of networking protocols designed to facilitate standards-based fixed/mobile, voice/data and voice/video convergence.

IMS will allow carriers to be able to combine the applications and capabilities of the Internet with both wireless and wire line telephony

IMS

Motivation The technology Applications

Motivation

User Needs: Economics, Quality & Convenience

Enterprise Needs: Interoperability and Remote access

Operator Needs : Convergence Service providers can deliver services

independent of their device type, network type, physical location

Standardization 3GPP, deals with the core elements.

Release 5 in 2002, framework for the session-based IP multimedia services in the W-CDMA, older GSM and GPRS networks.

3GPP release 6 added inter working with WLAN 3GPP release 7 added support for fixed networks 3GPP release 8 added support for Long Term

Evolution (LTE), IETF, defining protocols for network

elements to communicate Open Mobile Alliance (OMA), defining

applications.

IMS-The Technology

An Architectural framework designed to deliver “IP Multimedia Services” to end users

Delivering “Internet Services” over GPRS, Wireless LAN, CDMA and Fixed Line etc.

The concept of layered architecture transformed. IP Based core network that provides converged

multimedia applications across both wireless & wireline devices

A horizontal structure, containing a “Horizontal Control Layer” which isolates the “Access Network” from the

service layer in the “Core Network”

IMS architecture

IMS deployment

Access Network allows the user to connect to Core IMS network.

Core network is a connection of different functions, linked by standard interfaces and reference points.

Core Network consists of HSS (Home Subscriber Server) SLF (Subscriber Location Function) CSCF (Call session control functions) SIP Application Servers, Gateways, Media

Servers etc. IMS uses IMSI, TMSI, IMEI, MSISDN , IMPI and IMPU

as user identities.

Simplified IMS architecture

IMS Protocols include SIP, COPS, DIAMETER base protocol ,UDP, RTP, IP , HTTP etc. Open interfaces to let different sets of functions Interact.

IMS Protocols

SIP: Establishment of IP connections, initiate /terminate/modify user sessions

COPS: Ensure QoS DIAMETER: Interaction between

I-CSCF/S-CSCF with SLF/HSS UDP/RTP: Standardized format for

delivering audio + Video over Internet H.248

IMS Core Network

HSS: Master database containing subscription info of users, authentication & authorization

SLF: MAP User addresses when multiple HSS are used

Call/Session Control Function (CSCF)• P-CSCF• I-CSCF• S-CSCF

Call/Session Control Function P-CSCF• First POC for an IMS (/SIP) terminal• Accepts attach requests and forwards

them• Establishes IPSec association with IMS

terminal• Compresses/decompresses SIP messages• Authorizes Media resources via PDF

(Policy decision function)

Call/Session Control Function I-CSCF• Interacts with Remote servers• Forwarding point for SIP Packets within

an IMS network domain• Queries the HSS to retrieve the user

location (based on S-CSCF) and route the SIP Packet to assigned S-CSCF

Call/Session Control Function S-CSCF• Session Management• Interacts with HSS to download & Upload

Subscriber profile• Directs, as to which Application Server

(AS) the SIP message is to be forwarded• Multiple S-CSCF for load distribution• HSS assigns the S-CSCF to a user

Working of IMS network

The central position is occupied by the Call Session Control Function (CSCF).

It is further decomposed into Interrogating, Serving and Proxy Session Control Functions

The P-CSCF forwards SIP messages received from the User Equipment to the I-CSCF and/or S-CSCF

Contd… I- CSCF’s main purpose is to provide a service locator

function It also performs major functions like

Registration ,resource utilization , Acting as a Topology Hiding Inter network Gateway

The S-CSCF is essentially a SIP server that provides session control for subscribers.

It is responsible for interacting with network databases.

User signaling event is now forwarded to whatever application servers and/or gateways are required to complete the user-requested action.

IMS uses authentication for wireline- access security and uses the IETF’s HTTP Digest Authentication protocol for mobile network-access security.

IMS Call Flows

IMS RegistrationIMS Call flows\ims_registration.pdf IMS – IMS CallIMS Call flows\ims_to_ims_call.pdf IMS- PSTN CallIMS Call flows\ims-to-pstn-callflow.pdf

Application Servers

ATS (Advanced Telephony server)

IPCentrex (Enterprise, groups, Users)

MediaX3600 (Conference Calls)

Demands of End User

Most end users focus on four factors when making decisions

about which services to select

1. Economy2. Quality3. Convenience4. Utility and Leisure

Economy Does it save me money? Is it worth using funds that could be used for other things?

Quality Quality floor Quality Ceiling

Convenience Service should be available wherever and whenever

Utility and Leisure Service should meet their particular needs Should provide leisure activities (gaming etc)

IMS and End User Demands

Improved Economy Allows the end user to deal with one provisioning authority

(Common platform for service deployment & provisioning) One consistent transport network regardless of access

technology One service and billing department

Improved Quality There is a common IP-based core Service providers can support multiple access technologies The service provider can, therefore pick and choose the

most appropriate access vehicles to suit individual market areas

IMS and Convenience

During a voice call, they can upgrade to a video conference by selecting an upgrade code.

Utility and Leisure

IMS allows the end user to define groups that can be reached with a single number.

IMS gives new dimension to online gaming and audio services

Future Aspects

It is envisioned that many services will be delivered over IMS networks

Presence Presence is the ability to see the online status of the users.

Voice and Video Telephony Instant Messaging Push to talk, push to see Conferencing

Groups can be defined which can be accessed by a single number

Gaming Convergence of all of the above

Traditional information technology (IT) companies will find a lucrative new

market with IMS.

IMS Applications and Services

‘IMS has arrived; and with it, unprecedented access’. [Nortel]

IMS, based on the 3GPP IMS architecture, will enable new person-to-person services, which will enrich the way that people communicate with each other combining voice, imaging and video within a single session.

IP Multimedia Subsystem (IMS) will also enable new services between mobile and fixed devices.

Some examples of IMS based services Push to talk over Cellular (PoC), Combinational services (IMS services in addition to circuit switched voice), Presence, Instant Messaging, Voice Messaging, Video telephony, Multiplayer games, Converged Mobility

IMS Applications and Services

‘Technology Evolution’

PSTN

• Circuit switched • Analog• Digital• SS7• ISDN

• Circuit switched

• Analog

• Digital

• 2G (GSM & CDMAANSI-41)

3G WirelessWireless

• 3G wireless + IP ++

–Standard Services Platform

–Converged Applications & Content

–Access Independence

IPIMS

• Internet

–VoIP

–Instant Messaging

–Web Applications

• W-CDMA

• GPRS/UMTS

Push to Talk over Cellular (PoC)

Push to talk over Cellular (PoC) introduces a direct one-to-one and one-to-many voice communication service in the cellular network.

The PoC solution is based on the half-duplex technology and is built over the existing GPRS and EDGE networks.

An expansion of the Push To Talk service is Push To See and eventually Push To X (anything) involving content-sharing, location-based services and IMS applications across a number of different devices truly enabling enhanced real-time communications.

Before IMS… Relied on non-standardized Push to Talk over Cellular clients Proprietary solution, non-OMA Compliant

With IMS… Integrated with a network presence function, allowing users to see

the availability of other users Relies on standards-based Push to Talk over Cellular clients Standards-based solution that will allow roaming and inter-working

amongst carriers

Converged Mobility

IMS Converged Mobility unfetters communications from physical boundaries, freeing users to roam, seamlessly, with unbroken service.

Before IMS… Basic hand-off with limited voice support Voice-only solution No multimedia integration

With IMS… Addresses multiple market segments with a single solution Seamless handoff of voice and data across all networks and

solutions An open, standards-based solution Cellular and enterprise personal features and settings

converge

Multiplayer Gaming

Multiplayer Gaming offers richer end-user experiences and maximized attraction by allowing multiple players to participate.

It utilizes presence and group based services. Before IMS…

Lack of an integrated experience — voice, data and video

With IMS… A multiplayer gaming experience Truly integrated multimedia and communication capabilities to

enhance the gaming experience The ability to invite people to join games based on their

presence availability and status

Instant Messaging Services

Instant Messaging is a communication service that allows end-users to send and receive messages instantly.

Messages can contain any MIME type media content such as text, image, audio or video clips, application data or a combination of these.

The message is sent through the packet data network to the IP Multimedia Subsystem (IMS), which locates the terminating IP client and routes the message to the recipient.

An Instant Messaging service can offer a store-and-forward (S&F) function – if the message cannot be delivered to the receiver straight away, it can be stored in an S&F element in the IP Multimedia Subsystem, which will forward the message to the recipients when they become available.

Instant messages can also be delivered to non-IMS terminals via MMS.

Voice and Video Telephony IMS enabled Voice and Video calls are carried over a packet

core network (VoIP).

Video-conferencing Video-conferencing service extends the point-to-point video

call to a multi-point service. Videoconferencing requires an IMS conference bridge

service, which links the multiple point-to-point video calls together, and implements the associated service logic.

The conference bridge is not concerned about the underlying infrastructure and client devices and assumes that audio- and video connections are provided by the appropriate standard and that these connections are delivered over the IP network.

The advantages of IMS based applications

For Network Operators… new revenue opportunities cost savings

For End-Users… Rapid delivery of new services, regardless of application type Access to services anywhere, regardless of application Integration of the end-user experience Personalization of services, regardless of access

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