Networks and operators are migrating from the traditional “stove pipe” circuit switched networks to a converged “All IP” NGN core network. This harmonized All IP network has the potential to provide a completely new telecom business model for both fixed and mobile network operators.

A technical prerequisite for a converged network is a common service delivery platform that is independent from the access networks below. The 3GPP SIP-based IP Multimedia Subsystem (IMS) is defined for this purpose. Simply stated, IMS is a set of specifications that describes the Next Generation Networking (NGN) architecture for implementing multimedia services including IP based telephony. It also defines a complete architecture and framework that enables the convergence of voice, video, data, fixed and mobile network technology over an IP-based infrastructure.

IMS will be a key enabler for fixed/mobile convergence, reducing network installation and maintenance costs, and allowing new services to be rapidly developed and deployed to satisfy new market demands.

What does IMS provide?

In a nutshell, IMS provides:

• Sip Session control
• Messaging support
• Single sign on and user authentication
• Subscription handling
• QoS / Media Authorisation
• Signalling compression
• Charging Support
• Seamless Mobility Support
• Routing / Addressing Support
• Regulatory Service Support
• Conference Support
• PSTN Interworking Support

Who will use IMS?

Fixed line operators would probably gain more from an IMS architecture than Mobile operators. Traditional PSTN customers can be migrated from circuit switched Intelligent Networks (IN) to an IMS core through the use of a PSTN Emulation (PES) or PSTN Simulation (PSS). The end user would be oblivious to the changeover. Mobile users, and users with digital broadband handsets/softphones would benefit the most from an operators IMS network. Each IMS subscriber would have access to a variety of multimedia (and telephony) services, with flexible billing options and the freedom to seamlessly transfer voice and data sessions between devices. IMS enables the operator to offer subscribers ubiquitous connectivity, rapid and flexible service deployment on a future-ready network.

What are the benefits of IMS?

For operators:

• Seamless call handover between access networks (WiFi, 3G, WiMAX and GSM, etc)
• Fast creation of attractive services, deliver converged network agnostic, real-time, multimedia applications
• Standards based network architecture: Lower future CAPEX and OPEX costs
• Combines services from fixed, mobile and broadband networks
• Combine multiple media sessions (video, voice, music, pictures, text, data)
• Common, Integrated platform for fast cost-effective deployment of new services
• Customer retention by enriching their experience
• Real-time and non real-time centralised billing
• Flexible charging model

For subscribers:

• Transfer on-going calls to any device
• Guaranteed Quality of Service (QoS)
• Presence across all devices
• Seamless combination of real-time voice, text, video, images, games, Web, e-mail, and more
• Device independent person-to-person, person-to-content multimedia services

IMS Standardisation

TISPAN and 3GPP are now working together to define a harmonized IMS-centric core (Common IMS) for both wireless and wireline networks.

Architecture: TS 23.002 (3GPP Architecture), TS 23.221 (Architectural Principles)
IMS Session Control: TS 22.228 (IMS Stage 1), TS 23.228 (IMS Stage 2), TS 24.228 (Rel-5 SIP Signalling Flows), TS 24.229 (IMS Call Control)
IMS Services: TS 23.141, 24.141, 33.141 (Presence), TS 22.340, 24.247 (Messaging), TS 24.147 (Conferencing), TR 23.979 (PoC)
IMS Interworking to CS/PSTN: TS 29.163
IMS Interworking to SIP Clients in the Internet: TS 29.162, TR 29.962
IMS Charging: TS 23.815 (Charging/Architecture):TS 32.225, TS 32.235 (IMS Charging Data)
Security Mechanisms: TS 33.102 (Security Architecture), TS 33.203 (Access Security), TS 33.210 (Network Security), TS 31.103 (ISIM), TS 33.106, 33.107, 33.108 (Lawful Interception).
Evolution of Policy Control and Charging: TR 23.803
Fixed Broadband Access: TR 24.829

IMS services

Usage of SIP allows many two party, multi party, multimedia services in between users and application servers. E.g. VoIP, video calls, conferencing, instant and deferred multimedia messaging, pull & push streaming services, presence services, push to talk, click to dial, IPTV, etc.

Many fixed and broadband wireless operators have adopted an NGN/IMS as a basis for their core networks – this means that tomorrow’s multimedia mobile world will most likely be IMS based.

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