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Building an end-to-end architecture that supports fixed mobile convergence

Posted: 08 Sep 2005     Print Version  Bookmark and Share

Keywords:fixed mobile convergence  fmc  agere systems  ericsson 

By Deepak Kataria, Agere Systems

Dimitris Logothetis, Ericsson

Network Systems Designline

The concept of convergence emerges from telecom service providers' need to find new revenue streams, reduce their operating expenses and simultaneously invest in future-proof network architectures and technologies. Some service providers are looking for a multitude of new services including mobile and fixed access, while others seek only a combination of TV, Internet access and telephony.

There are numerous standards activities that contribute to the concept of convergence. From the wireless perspective, the 3G Partnership Project (3GPP) has standardized the IP Multimedia Subsystem (IMS)1,2. IMS is an architecture that will allow emerging IP multimedia applications to run over a GPRS/UMTS environment. A group called the 3GPP2 Forum also is standardizing a similar architecture, which is a subset of the 3GPP2 IP Multimedia Domain (MMD) 3,4. Much of the 3GPP's IMS work is reused and/or adopted in the 3GPP2 IMS standards process. On the fixed network side, the ETSI Telecoms & Internet Converged Services and Protocols for Advanced Networks (TISPAN) Group was formed to develop standards for next-generation fixed networks and the evolution to FMC.

The underlying transport technology for convergent networks and applications is Internet Protocol (IP). IP brings the globally successful Internet service creation environment and paradigm into next-generation wireless and fixed wireline networks. The signaling protocol that will enable users to access networks and experience services is session initiation protocol (SIP). SIP is an application layer protocol that can establish, modify and terminate multimedia sessions over the Internet.5

On the access side, technologies and standards continue to evolve and become more mature. On the fixed side, for example, broadband access on digital subscriber lines (DSL) promises speeds of up to 24Mbps downstream and up to 3Mbps upstream using the latest ADSL2+ standard.6 The DOCSIS 3.0 initiative, launched by CableLabs in late 2004, promises to deliver 200 Mbps to end users by grouping multiple 6 MHz television channels into a single wideband carrier.

The emerging WiMAX standards7 deliver bandwidth and coverage under non-Line-of-Sight (NLOS) conditions and promise what other broadband wireless access (BWA) technologies have failed to achieve: coverage, bandwidth and cost-effective terminals and base stations. As 3G cellular networks are deployed and become mature, new 3GPP-promoted access technologies such as high speed downlink packet access (HSPDA) 8 and high speed uplink packet access (HSUPA) promise to increase downlink and uplink speeds respectively.

For CDMA2000 systems, the 3GPP2 recently completed the enhanced reverse link standardization effort of the 1 x Evolution for High Speed Integrated Data and Voice (1xEV-DV) access technology that will deliver increased bandwidth in the upstream direction. 9

Finally, a key factor for integrating all different applications under a common IP-based transport network is traffic management. Mechanisms such as IP Diffserv/Intserv, multiprotocol label switching (MPLS) and policy-based networking will interwork with QoS mechanisms defined in access networks (wireline and wireless) to provide the concept of end-to-end QoS support, which is critical to multiservice and converged networks.

This article will present the network architecture that will enable fixed mobile convergence and address key issues that remain to be resolved by standards groups and the research community.

Definition and issues

FMC can be defined as the merging of wireline and wireless networks and services. Three aspects of these networks are merging:

• Network

• Services

• Terminals

Network convergence could be further divided between the access network and the core network. Network convergence means the same network will be used for fixed and mobile services and by both types of operators. Currently, network service providers could, in principle, share transmission/transport infrastructures.

Optical Sonet/SDH/WDM and microwave transmission infrastructures could be common for fixed and mobile operators, thereby making convergence at the "physical" layer feasible today. Furthermore, this convergence could be extended for packet services with operators sharing ATM and IP network infrastructures.

The new notion of network convergence is that service providers should be able to share network infrastructure above and beyond the straight-forward transmission/transport "pipes" and extending to network control and intelligence. In fact, the architecture that will enable this network convergence is commonly referred to as a layered architecture (see Figure 1).

Figure 1: The layered architecture concept

The layered architecture concept introduces common connectivity and control layers for all access types and all services. Access networks (i.e., DSL, GSM Radio Access Network, WiMAX, etc.) may require a core network adaptation due to transport or protocol incompatibilities. These elements are called media gateways.

Access methods have been traditionally positioned with either fixed or mobile networks. Recently, however, newly introduced access methods such as WLAN, WiMAX and Unlicensed Mobile Access (UMA) can be associated with either fixed or mobile access.

On the services side, voice remains the most obvious and widely used service in both fixed and mobile networks. Voice service is, in effect, a convergent service because it can be offered across both networks. Other services, however, such as short messaging service (SMS) and instant messaging (IM), have been associated with specific networks, e.g. mobile or fixed.

The notion of service convergence is to introduce new services in a transparent way over both networks; as well as introduce combined services, such as new services that consist of two or more basic services.

Network architecture

A variety of access technologies, both wireline and wireless, have been adopted, or, they are under development in standards bodies or other forums. These technologies address issues such as bandwidth, applications, and quality of service.

In the wireline arena there are access technologies such as xDSL, DOCSIS and FTTH that deliver similar or even higher bit rates to users on telephony DSL lines, coaxial cables for TV distribution, and optical fibers, respectively.

Some of the access technologies that will play a vital role in a fixed-mobile convergence environment include:

Digital subscriber line (DSL) has been around for several years, and it continues to evolve. The most recently standardized (ITU G.992.5) asymmetric flavor is called ADSL2+. The new standard promises to deliver up to 24Mbps downstream, and up to 3 Mbps upstream. Because of its high potential bandwidth, DSL is one of the most important access methods for true converged multimedia applications in cases where good quality copper is available.

Wireless local area network (WLAN) access provides a low-cost, high-bandwidth method for data today, and other multimedia applications in the future. Operators in the North America, Europe and Asia are offering WLAN access in hot-spots for Internet access. Voice over IP (VoIP) is soon to come. Long-awaited roaming with 3G networks makes WLAN a key access technology for fixed-mobile convergence. A user with WLAN access either at home, or at an enterprise or pubic location, could be connected through appropriate multi-access (WLAN and cellular) terminals to the Internet, to the PSTN, or to mobile network(s).

Wireless Interoperability for Microwave Access (WiMAX) can be thought as an initiative to provide cost-effective interoperable products and solutions for broadband wireless access (BWA). More specifically, IEEE 802.16 has enhanced its specifications to accommodate interoperable products in the 2 - 11 GHz frequency band range. The first specification IEEE 802.16-2004 is now ready, and WiMAX certified products are expected in 2005. Completion of 802.16e, which will accommodate mobility, is expected in 2005.

Unlicensed Mobile Access (UMA) is a set of specifications created by a group of vendors and operators to create bearer-agnostic access to cellular networks. In the proposed initial version of the standard, a mobile device is equipped with a non-cellular radio and connects to an UMA Network Controller (UNC).

Using IPSec, it creates a secure tunnel into the cellular network. Using this approach, the cellular network utilizes existing protocols for AAA as defined in 3GPP without the need to define any new protocols. A recent important development is the inclusion of the UMA concept in the 3GPP R6 specifications under the term Generic Access Network (GAN) in TS 43.318 within the GERAN set of standards.

Core network technology development

Until recently, wireless, wireline, data and cable TV networks have been separate from one another. Next-generation solutions represent a more efficient way to build networks using a common multiservice layered architecture. They will have a service layer, a control layer, a backbone layer and access layer.

Having one converged network for all access types is a significant benefit of the layered architecture concept. It can improve service quality and allow the efficient introduction of new multimedia services based on IMS. Service providers can increase network efficiency using optimized transport and coding solutions and will not need the extra-capacity required when the networks are operated separately.

Significant cost savings can arise from having one network with fewer nodes and lower operating costs. From an investment perspective, it is possible to optimize use of control and media processing resources, reducing the need to replace technologies and the cost of network updates.

A converged network using IMS allows the following resources to be shared, regardless of service or access type:

• Charging

• Presence

• Directory

• Group and list functions

• Provisioning

• Media handling

• Session control

• Operation and management

In addition to making converged user services faster and easier to introduce, common shared resources increase operational network efficiency. The network evolution path is unique for each operator and depends on many factors, including the business environment, cultural heritage, regulations, end-user behavior and PC and mobile penetration rates. The transformation is usually done step-by-step towards the target network with an all-IP solution based on IMS.

Next-gen networks

The term next generation network (NGN) has been used by the telecom industry to denote networks that will offer telecom-grade voice services using packet-switching transport technology such as ATM or IP. Furthermore, the call control function is separated from the switching function. The packet switching transport can be present in either the core network or both the core and access network, i.e., the user will receive VoATM or VoIP service.

For this reason, TISPAN was formed to define the NGN framework, and, in particular, to provide a multi-service, multi-protocol, multi-access, IP-based network. This network is designed to be secure, reliable and trusted. It is also designed to be enable service providers to offer real-time and non-real time communication services between peers or in client-server mode. These services include mobility/portablity/nomadic use of devices users' personalized communication services at any place and using any type of terminal.

The standard is being planned with three releases:

• Release 1 addresses nomadicity and user-controlled roaming based on use of an access network attachment subsystem and DSL/WLAN access methods.

• Release 2 optimizes resource usage according to user subscription profile and service use.

• Release 3 introduces full nomadicity and high-bandwidth access methods such as VDSL, FTTH and WiMAX.

End-to-end network architecture

The end-to-end network architecture shown in Figure 2 shows various access networks, both radio-based (GSM, CDMA, WLAN and WCDMA) and DSL-based. The connectivity layer contains nodes such as:

• SGSN and GGSN for the UMTS network

• PDSN for the CDMA network

• Media Gateways (MGW) for PSTN interconnection

• Session Border Gateways (SBGs) for NAT

• Firewall traversal of SIP flows for:

a) the DSL-based network (A-SBG)

b) mobile networks (M-SBG)

c) other network peering (N-SBG)

As far as the control layer is concerned, IMS control is shown with associated elements as well as with interworking to a softswitch solution. Finally, a policy control engine for the fixed DSL-based broadband is shown.

Figure 2: End-to-end network architecture

A fundamental issue for the end-to-end network architecture is traffic management and, in particular, how QoS is supported on a end-to-end basis and across different access networks. IP core network mechanisms such as Diffserv/Intserv, MPLS and policy-based networking need to interwork with QoS mechanisms specified in a 3GPP/3GPP2 radio access network (RAN), a WLAN or a WiMAX network.

Network processors play a vital role in accomplishing this interworking function in a flexible and future-proof way, as opposed to customized ASIC design, which is often expensive in a world of continuously evolving standards.

Services convergence

Convergence of services and applications implies that the same service can be accessed from different types of terminals, for example sending messages from a mobile user to a PC, or browsing the Internet from a handheld mobile phone, or different types of networks, including cable TV, mobile or fixed.

As mentioned earlier, IMS, the standardized solution for SIP-based applications for multiple access network types, is a key component for delivering converged services with telecom-grade quality of service. IMS makes it possible to increase network efficiency and catalyzes the faster and simpler introduction of new services. The common service execution environment of IMS supports user applications available over multiple access types (access-aware service platforms). There will be one common user- and services-management function, a common charging system, and a common identification/ authorization system.

Presence enables a paradigm shift in person-to-person communication, and is a key component for many IMS-based services. Presence-aware communication allows users to see recipients' information before connecting with them (e.g. availability, geographical position). Presence enables the user to see possible communication alternatives based on device and network capabilities. Presence information will be available from any device (mobile, PC etc.).

The majority of communication sessions using converged services, such as voice calls, video calls, chat sessions, file transfers, on-line games and white board sessions, are typically initiated via the active phonebook. The active phone book is one application that uses the presence information from IMS.

Device convergence

Device evolution can be seen as a mirror of the core and access network evolution. It is in the device that new applications are made available and where identification and security mechanisms are implemented. Therefore, it is also where access capabilities need to exist. Another possible functionality for mobile device convergence, in the short/medium term, is adding support for UMA.

Storage requirements and capabilities will dramatically increase in both devices and networks. Some key network characteristics also must be available to devices connected to the fixed network. The evolution of connected home networks along with various applications, such as interactive TV, games, music downloads, shopping and home security will require some of the characteristics delivered by IMS (e.g. quality of service, user management, charging and security).


The above describes the current situation in the standards area for fixed and mobile networks, and a variety of access alternatives for both types of networks. It also discusses recent developments that will enable fixed - mobile convergence in the future, namely the UMA initiative. This initiative is currently positioned as GAN in 3GPP and the IMS architecture as defined in the 3GPP R5 and R6 and 3GPP2 MMD specifications. There are similar activities for NGN in ETSI TISPAN standardization activities and the ITU's NGN Focus Group. The target network architecture is then shown with numerous access methods and services built on top of IP control intelligence.

Finally, IP-based traffic management is a vital component for the success of a multiservice and converged network. And there is a need for QoS mapping/interworking between different access networks and IP core network.

About the authors

Deepak Kataria is systems integration engineering manager for Agere Systems. He can be reached at

Dimitris Logothetis is systems solution manager for Ericsson Greece. He can be reached at


1 3GPP. Technical Specifications Group Services and System Aspects. Service Requirements for the IP Multimedia Core Network Subsystem, Release 5. TS 22.228.

2 3GPP. Technical Specifications Group Services and System Aspects. IP Multimedia Subsystem Stage 2, Release 5. TS 23.228.

3 3GPP2. IP Multimedia Domain System Requirements. 3GPP2 S.P0058.

4 3GPP2. IP Network for CDMA2000 Spread Spectrum Systems. 3GPP2 all-IP Core Network Enhancements for Multimedia Domain (MMD) Overview, 3GPP2 X.P0013.0.

5 J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley and E. Schooler. SIP: Session Initiation Protocol. IETF RFC 3261, June 2002.

6 ITU-T Recommendation G.992.5. Asymmetric Digital Subscriber Line (ADSL) transceivers - Extended bandwidth ADSL2 (ADSL2+).

7 A. Ghosh, D. Wolter, J. Andrews and R. Chen. Broadband Wireless Access with WiMAX/802.16: Current Performance Benchmarks and Future Potential. IEEE Communications Magazine, February 2005.

8 3GPP UTRA High Speed Downlink Packet Access (HSDPA). Overall Description. Stage 2. TS 25.308.

9 3GPP2. Physical layer Standard for CDMA2000 Spread Spectrum Systems Release D. C.S0002-C V1.

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