Miikka Poikselkä works for Nokia Siemens Networks, Finland.

Georg Mayer works for Nokia Mobile Phones, Finland. 

All the authors are involved with Third Generation Partnership Project Agreement (3GPP), Internet Engineering Task Force (IETF) and Open Mobile Alliance (OMA) standardization. 

The IMS: IP Multimedia Concepts and Services 3rd Edition

By Miikka Poikselk Georg Mayer

John Wiley & Sons

Copyright © 2009 John Wiley & Sons, Ltd
All right reserved.
ISBN: 978-0-470-72196-4

Chapter One

Introduction

1.1 What is the Internet Protocol Multimedia Subsystem (IMS)?

Fixed and mobile networks have gone through a major transition in the past 20 years. In the mobile world, first-generation (1G) systems were introduced in the mid-1980s. These networks offered basic services for users. The main emphasis was on speech and speech-related services. Second-generation (2G) systems in the 1990s brought some data services and more sophisticated supplementary services to the users. The third generation (3G and 3.5G) and its evolution (LTE) is now enabling faster data rates and various multimedia services. In the fixed side, traditional Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN) networks have dominated traditional voice and video communication. In recent years the usage of the Internet has exploded and more and more users are taking advantage of faster and cheaper Internet connection such as Asymmetric Digital Subscriber Line (ADSL). These types of Internet connections enable always-on connectivity, which is a necessity for people to start using real-time communication means – e.g., chatting applications, online gaming, Voice over IP (VoIP).

At the moment we are experiencing the fast convergence of fixed and mobile worlds as the penetration of mobile devices is increasing on a yearly basis. These mobile devices have large, high-precision displays, they have built-in cameras and a lot of resources for applications. They are always-on always-connected application devices. This redefines applications. Applications are no longer isolated entities exchanging information only with the user interface. The next generation of more exciting applications are peer-to-peer entities, which facilitate sharing: shared browsing, shared whiteboard, shared game experience, shared two-way radio session (i.e., Push to Talk Over Cellular). The concept of being connected will be redefined. Dialling a number and talking will soon be seen as a narrow subset of networking. The ability to establish a peer-to-peer connection between the new Internet Protocol (IP) enabled devices is the key required ingredient. This new paradigm of communications reaches far beyond the capabilities of the Plain Old Telephone Service (POTS).

In order to communicate, IP-based applications must have a mechanism to reach the correspondent. The telephone network currently provides this critical task of establishing a connection. By dialling the peer, the network can establish an ad hoc connection between any two terminals over the IP network. This critical IP connectivity capability is offered only in isolated and single-service provider environments in the Internet; closed systems compete on user base, where user lock-in is key and interworking between service providers is an unwelcome feature. Therefore, we need a global system – the IP Multimedia Subsystem (IMS). It allows applications in IP-enabled devices to establish peer-to-peer and peer-to-content connections easily and securely. Our definition for the IMS is:

IMS is a global, access-independent and standard-based IP connectivity and service control architecture that enables various types of multimedia services to end-users using common Internet-based protocols.

True integration of voice and data services increases productivity and overall effectiveness, while the development of innovative applications integrating voice, data and multimedia will create demands for new services, such as presence, multimedia chat, push to talk and conferencing. The skill to combine mobility and the IP network will be crucial to service success in the future.

Figure 1.1 shows a converged communication network for the fixed mobile environment. It is the IMS which introduces multimedia session control in the packet-switched domain and at the same time brings circuit-switched functionality in the packet-switched domain. The IMS is a key technology for such network consolidation.

1.2 Fixed and Mobile Convergence

Since the IMS architecture integrates both wireless and wireline networks, the IMS becomes an inexpensive medium for Fixed to Mobile Convergence (FMC). It is currently one of the crucial strategic issues in the telecommunications industry. Trends in different regions and countries are different, but on a global level operators are facing increasing competition and declining prices for voice traffic, fixed lines and fixed minutes. At the same time, mobile voice traffic is growing rapidly and substituting that of voice traffic over fixed lines. End users now expect high quality with reliable mobility and are using the Internet more as the penetration of broadband grows rapidly. Now, Voice over IP (VoIP) is starting to substitute PSTN. Meanwhile, key enabling technologies, such as smart phones, wireline and wireless broadband and IMS for seamless service over different access types are readily available. Combined, this means that operators are looking for long-term evolutionary strategies towards converged, access-agnostic networks, with service integration and interoperability across domains and devices. From the end user’s perspective this delivers seamless end user experience across multiple locations, devices and services. Convergence can be viewed from three separate angles:

convergence of networks

convergence of services

convergence of devices

Convergence of Networks

Network convergence simplifies the end user experience and dissolves the barriers and complexities that separate today’s network islands. The same services are available across all networks and, in an ideal world, appear and perform in exactly the same way, making usage easy, transparent and intuitive.

From an operator’s perspective, the goal of network convergence is to migrate today’s separate PSTN, PLMN, backbone and IP networks to a fully converged network that supports any access technology. The full evolution includes a cost effective migration to an All-IP network using IMS as the unifying platform, allowing all new services to be accessed in a standard and consistent manner as shown in Figure 1.2 manner. Advancing in this evolution will be the key to an operator’s ability to reduce OPEX and CAPEX, and increasing competitiveness and profitability.

Many locations, such as homes, enterprises and public places already have access networks available (xDSL, WLAN, cable etc.). When operators launch new services such as video streaming or hosted email they can take advantage of these existing networks, extending service access to more potential subscribers. In turn this will mean launching services to new market segments for new revenue opportunities. With multiple access networks operators can attract existing and new customers with an enhanced convergence service portfolio using unified billing.

A converged core network is the key enabler for converged networks. Multi-access to a common, converged core network enables cost optimization for both mobile and hybrid operators. Re-use of existing access network infrastructure and integration with the service infrastructure results in both OPEX and CAPEX savings. And multi-access enables operators to introduce end-to-end quadruple-play services (voice, data, video/TV and mobility), to new customers.

IP-based access connection using the SIP protocol between the device and the converged core network – so called ‘Native IP access’ – allows voice, video and other multimedia applications over any access network. Native IP access supports a wide variety of applications in different devices, including mobile handsets, PC clients and SIP desktop phones. POTS phones too, can also be supported, via a connection to an SIP-capable DSLAM or analog terminal adapter (ATA). Native IP access architecture allows the introduction of new rich IP multimedia services through IMS functionality, such as presence, media push, multimedia telephony, games and various other SIP enabled applications, furthering revenue streams for operators.

Device Convergence

Typically, a device is only used – in the main – for a single purpose and the support for its other functions is limited. PSTN phones, low end mobile phones and set-top boxes are good examples. Consumers use these devices for a single purpose. When they change tasks they change device and access network. This means service islands, which lead to mis-matched user experiences from different public and private networks. What’s needed are unifying devices that can access services in a similar and easy way.

Smart phones are serious contenders for voice-plus multimedia services in a truly mobile environment. Multiple radio interfaces provide access over circuit and packet-switched networks (cellular, WLAN etc) and IMS allows services and applications to traverse different IP networks. Mobile phone development has been rapid in the last decade and new models take increasing advantage of new technologies. They incorporate the enhanced colour displays and high quality imaging features needed to support service consumption and the creation of own content. Plus the exponential growth of memory capacity and processing power means that smart phones can now replicate the applications currently employed in notebook PCs and PDAs.

Consumers want the quality of fixed services with the flexibility of mobile and convergence lets this happen, by allowing service access through the most suitable access network, and by letting consumers choose the best device for the service. In many cases that device will be a smart phone, but it could just as easily be a PC or laptop with VoIP software or converged fixed clients who can share IM, presence etc with mobile devices, a fixed VoIP phone or even a TV with a set-top box.

Service Convergence

The mobility model has become ‘me-centric’, with my phone book, my contact information, my agenda, my messages, my availability and preferred communication method, my Internet, my pictures and video clips (received and shared), my personal and business email, my wall-paper, my music and so on. Multimedia services, such as Presence, Push-to-talk, messaging, interactive applications, data or video sharing plus streaming, browsing and downloading, are being delivered over fixed and mobile packet networks. To launch new services and applications quickly, operators can use IMS to eliminate the complexity of different service platforms in the network. Standards based Service Delivery Framework (SDF) provides comprehensive lifecycle management, making the launch of new services and applications quicker and easier to integrate and operate; delivering solutions more speedily to market and reducing the total cost of ownership. In effect the operator can provision – and the end-user quickly and conveniently self-provision – the new services.

VoIP and Instant Messaging are two developments that helped kick-start service convergence. VoIP has had a seismic impact on telephony within enterprises and, as the penetration of broadband access increases, so does the availability of this transport mechanism within the home. Users also benefit from personalized VoIP, including same number, same contacts and the same supplementary services like call barring, call waiting, ring back tones, one voice mail, option for one postpaid bill or prepaid account, etc through any access network. IP DSLAMs are letting operators offer both DSL access and traditional two-wire POTS connections using a SIP client in the DSLAM. This development and others like fixed VoIP phones, Analog Telephony Adapters (ATA) and fixed soft switches place fixed line operators in an excellent position. They can offer multimedia services via DSL and attractive tariffs for analog POTS connected to an IP network, thereby maintaining existing services where required and evolving the core network to an IP-based solution. Smart phones, on the other hand, have WLAN interfaces so they can access fixed broadband networks. This allows the mobile phone to be used as an IP phone and users to continue employing their personalized services at home, or via WLANs, connected to DSL, in hot spots or offices. Convergence in this case enables a practical combination of cellular and fixed broadband access. The user experience doesn’t change: the same voice and multimedia services are used in the same way. Fixed to Mobile Substitution and fixed VoIP are gradually replacing PSTN voice telephony. Multimedia services are being delivered over fixed and mobile packet networks. Operators must now decide on the kinds of services they wish to provide by themselves or by partners, to whom and in which regions. And what they might offer is no longer limited to traditional telecom services only, but perhaps entry into new businesses.

1.3 Example of IMS Services

Switching on my Internet Protocol Multimedia Subsystem (IMS) enabled device, it will automatically register to the IMS network using information in the identity module (such as USIM). During registration both device and network are authenticated and my device will get my user identities from the network. After this single registration, all my services will be available, including push to talk, presence, voice and video sessions, messaging and multiplayer games. Moreover, my availability information is updated at the presence server as being “online” and listing my current applications.

When I need to contact my friend Bob, I select Bob from my device’s phone book and, based on his presence information, I see immediately that he is available. After pressing the ‘green button’ on my device it will place an ‘ordinary’ call to him. The IMS network will take care of finding and setting up a Session Initiation Protocol (SIP) session between our devices, even though Bob is currently abroad. When my call reaches Bob’s terminal he will see that the call is coming from me and, additionally, he sees a text string inserted by me (‘Free tickets to movie next Wednesday’). Bob answers, but tells me that he’s not sure whether he is able to come. We decide to check the issue again on Sunday. Before hanging up, Bob says to me, ‘You won’t believe what I saw today but just wait a second, I’ll show you.’ Bob starts streaming a video clip to me, and while I’m watching the video, Bob keeps explaining what happened in the zoo earlier that day.

Mike realizes that today is the birthday of his good friend Jill. Although he’s travelling and can’t meet her today, he wants to send Jill a personal birthday message. While Mike is sitting in a local coffee shop enjoying coffee and reading the latest news from the Internet using his brand-new Wireless Local Area Network (WLAN) device, he decides to send her a video clip as a birthday greeting. Jill is having a bath when she hears her phone ringing. She sees that she has received a message and checks it. She saves the video clip and decides to send something in return. Knowing that Mike knows her weird sense of humour, she sends a picture of herself taking a bath (Figure 1.3).

Peter Simpson is a Londoner and a die-hard Arsenal fan. With sheer luck he has managed to get tickets to an Arsenal-Tottenham derby and sets off to see the game. There he is, sitting at the stadium during the match, when suddenly he gets an irresistible urge to make his friend envious. He gets his mobile phone and makes a call to his friend John Clark, a Tottenham supporter. John is sitting at his desk and receives an incoming call pop-up on his PC screen, informing him that Peter is calling. He answers and they start to talk. Peter can’t contain himself and starts the video-sharing application while zooming onto the field. John receives an incoming video request and accepts the stream. The PC client starts to show the game, and with a pang of jealousy and disappointment John watches Arsenal score. ‘Nice goal, huh?’ asks Peter. ‘It ain’t over yet,’ says John, gritting his teeth, and ends the video stream. They continue to argue good-naturedly about the game and their teams over the phone. Figure 1.3 Multimedia messaging

All the required communication takes place using the IP connectivity provided by the IMS as shown in Figure 1.4. The IMS offers the capability to select the best and most suitable communication media, to change the media during the session spontaneously, and use the preferred (SIP-capable) communication device over any IP access.

(Continues…)

Excerpted from The IMS: IP Multimedia Concepts and Services 3rd Editionby Miikka Poikselk Georg Mayer Copyright © 2009 by John Wiley & Sons, Ltd. Excerpted by permission.
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