Fixed Mobile Convergence: Network architecture, Services, Terminals, and Traffic Management

Fixed Mobile Convergence: Network architecture, Services, Terminals, and Traffic Management Deepak Kataria Agere Systems Allentown PA 18109, USA Dimitris Logothetis Ericsson Hellas Athens 19002, GREECE Abstract-Fixed Mobile Convergence is a topic that is receiving significant attention from the research community as well as telecom equipment vendors around the world. The paper surveys standardization activities and proposes an end-to-end architecture that will support this architecture. The role of traffic management IP-based Quality of Service is recognized as a vital component for the success of a multiservice, IP-based and converged network. Index Terms-Fixed Mobile Convergence, traffic management, services, terniinals. I. INTRODUCTION uring the past few years a new topic that has received.l/significant attention in the telecom industry and the research community is that of fixed mobile convergence. The concept of convergence emerges from basic telecom service provider needs to find new revenue streams, reduce their operating expenses and, simultaneously, invest in future-proof network architectures and technologies. Service providers are looking for a multitude of new services, including some available for both mobile and fixed access. Others will represent a combination of TV, Internet and telephony, all of them converged services. Simultaneously, numerous standards activities contribute to the concept of convergence. Specifically, the 3G Partnership Project (3GPP) has standardized the IP Multimedia Subsystem (IMS) [1,2], an architecture that will allow emerging IP multimedia applications to run over a GPRS/UMTS environment. At the same time, the 3GPP2 Forum is also standardizing a similar architecture, a subsystem of the 3GPP2 IP Multimedia Domain (MMD) [3,4]. Much 3GPP IMS work is reused and/or adopted in the 3GPP2 IMS standards process. Furthermore, the ETSI TISPAN (Telecoms & Internet Converged Services and Protocols for Advanced Networks) Group was formed next generation networks and Fixed Mobile Convergence from the "fixed" perspective. Using a series of releases, the TISPAN_NGN Working Group plans to introduce multimedia services with nomadicity and user-controlled roaming, optimize resource usage according to user subscription profile and service usage, as well as full nomadicity (inter-network domain nomadicity) introduction in 2007. TISPAN will also adopt 3GPP IMS as part of its architecture but will also accommodate legacy fixed services such as PSTN/ISDN services [5]. The underlying transport technology for convergent networks and applications is obviously Internet Protocol (IP) that promises to bring the globally successful Internet service creation and paradigm into the wireless as well as next generation fixed networks. Additionally, the signaling protocol will enable users to access networks and experience services is the Session Initiation Protocol (SIP), the application layer protocol that can establish, modify and terminate multimedia sessions over the Internet [6]. Finally, 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 up to 24 Mbps downstream and up to 3 Mbps upstream using the latest ADSL2+ standard [7]. 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. Meanwhile, the emerging WiMAXFM standards [8] deliver bandwidth and coverage under non-line-of-sight (NLOS) conditions and promise what other Broadband Wireless Access (BWA) technologies had failed to achieve in the past, such as coverage, bandwidth and cost-effective terminals and base stations. On the wireless side, as 3G networks are deployed and become mature, new 3GPP promoted access technologies such as High Speed Down Link Packet Access (HSPDA) [9] 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 (1 x EV- DV) access technology that will deliver increased bandwidth in the upstream direction [10]. Finally, a key factor for the integration of all different applications under a common IP-based transport network is traffic management. Mechanisms such IP Diffserv/Intserv, 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, critical for multiservice and converged network. In this paper we will present the network architecture that will enable fixed mobile convergence. We will also address key issues that remain to be resolved by the standard bodies or the research community. 978-3-8007-2909-8/05/$20.00 2005 IEEE 2289

II. FIXED MOBILE CONVERGENCE DEHNITION AND ISSUES Fixed Mobile Convergence can be defined as the merging of wireline and wireless networks and services. More specifically, (see Figure 1), we can identify three different aspects of merging, namely, Netvork, Services and Terminals. Network convergence could be further divided between Access Network and Core Network Convergence. Network Convergence means that the same network will be used for fixed and mobile services and operators. Network service providers currently could, in principle, share transmission/transport infrastructures. Optical SONET / SDH / WDM and microwave transmission infrastructure 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 infrastructure. The new notion of network convergence is that service providers would be able to share network infrastructure above and beyond the straight-forward transmission / transport "pipes" extending to the network control and intelligence. In fact, the architecture that will enable this network convergence is commonly referred as layered architecture (see Figure 2). 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. We will address these methods later in the paper. On the services side, voice remains the most obvious and widely used service in fixed and mobile networks, Voice 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, have been associated with a specific network, fixed or mobile. The notion of service convergence is to introduce new services in a transparent way over both networks; as well as introduce combined services, i.e., a new service that consists of two or more basic services. We will discuss this concept later in the paper. III. FIXED MOBILE CONVERGENCE NETWORK ARCHITECTURE In this section we describe the architecture of a fixed mobile convergent network. To reach the target network, we first survey the enabling technologies for such a network both in the access part and core network part and cover issues on Next Generation Networks (NGN) as addressed in standards for wireiine networks in ETSI and ITU. A. Enabling Technologies 1) Access technologies development A variety of access technologies, both wireline and wireless, have been either adopted or are under development in standard bodies or other forums. These technologies are addressing issues such as bandwidth, applications, and quality of service. In the wireline area there are access technologies like xdsl, DOCSIS, FTTH that deliver similar or even larger bit rates to users on telephony digital subscriber lines, coaxial cables for TV distribution, and optical fibers, respectively. Figure 3 compares wireless technologies in terms of bandwidth and coverage. We now discuss some of these access technologies that we believe will be play a vital role in a fixed-mobile convergence environment in some more detail. a) DSL Digital Subscriber Line (DSL) technologies have been around for a while but continue to evolve. The most recently standardized (ITU G.992.5) asymmetric flavor is called ADSL2+ that promises to deliver up to 24 Mbps in the downstream direction and up to 3 Mbps in the upstream direction. Symmetric versions such as SHDSL and VDSL are also available but less widespread. Because of its large potential bandwidth, DSL is one of the most important access methods for true converged multimedia applications in cases where good quality copper is available. b) WLAN Wireless Local Area Network (WLAN) access method provides a low-cost high-bandwidth method for data and in the future other multimedia applications. The most popular and widely adopted standard, IEEE 802.11b has or currently is being enhanced to accommodate things like larger bandwidth (802.11g/802.11n), Quality of Service (802.11e), security (802.11 i) and roaming capability with 3G networks (802.11 u). Operators in the North America, Europe and Asia are offering WLAN access in hot-spots for internet access and soon to come Voice over IP. The long-awaited roaming with 3G networks makes WLAN a key access technology for fixedmobile convergence. A user with WLAN access either at home, or at an enterprise location or in another public location could be connected through appropriate multi-access (WLAN and cellular) terminals to the Internet, to the PSTN or to the mobile network(s). c) WiMAX 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, the IEEE 802.16 is enhancing its specifications to accommodate interoperable products in the 2-11 GHz frequency bands. The first specification 802.16 REVd (now renamed to IEEE 802.16-2004) is now ready and products are expected in 2005. The 978-3-8007-2909-8/05/$20.00 2005 IEEE 2290

version that will accommodate mobility 802.16e is also expected in 2005. d) UMA Unlicensed Mobile Access (UMA) is a set of specifications created by a group of vendors and operators to create a beareragnostic 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. The GAN architecture includes: A dual radio mobile station with a GSM/EDGE radio and a short-range unlicensed radio with software to control handoff between networks The GAN Controller (GANC) with a security gateway and interface specifications to GSM MSC, GPRS/3G SGSN and AAA proxy/server called A, Gb, Wm, respectively. 2) Core Network Technologies Development Until recently networks for wireless, wireline, data and cable TV services have existed in isolation. Next-generation solutions represent a more efficient way to build networks using a common multi-service layered architecture. The networks will have a layered structure with a service layer, a control layer, a backbone layer and access networks. Having one converged network for all access types is a significant benefit of layered architecture. This can improve service quality and allows 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 over-capacity required when the networks are separated. 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, hence reducing the need to replace technologies and the cost of network updates. Thus being a cornerstone in a converged solution. Figure 4 shows a network architecture based on IMS as defined in 3GPP. Various nodes are shown, with the central node being the Call State Control Function (CSCF), which is the SIP Server. CSCFs can be divided into three parts, namely Serving CSCF (S-CSCF), proxy CSCF (P-CSCF) and interrogating CSCF (I-CSCF). The S-CSCF is responsible for registration, session control and interactions with application servers. The Media Gateway Control Function (MGCF) and IM Media Gateway (IM-MGW) are responsible for signaling and media interworking, respectively, between the PS domain and circuit switched networks. The Multimedia Resource Function Processor (MRFP) controls the bearer including processing the media streams and is controlled by the Multimedia Resource Function Controller (MRFC). Finally, the Breakout Gateway Control Function (BGCF) interfaces to external PSTN networks. More details about the IMS architecture can be found in [2]. 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, as described later, the common shared resources also increase operational efficiency in the network. 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. 3) Next Generation Networks (NGN) The term Next Generation Networks (NGN) has been used by the telecom industry to denote networks that will offer telecom-grade voice services using a packet-switching transport technology as ATM or IP. Furthermore, the call control function is separated from the switching function. The packet switching transport could 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, the Telecommunication and Internet Converged Services and Protocols for Advanced Networking (TISPAN) was formed to define the Next Generation Network (NGN) to provide a multi-service, multi-protocol, multiaccess, IP-based network-secure, reliable and trusted, an enabler for service providers to offer real-time and non-real time communication services between peers or in a clientserver mode, mobility/nomadicity of both users and devices, and a user's personalized communication services anywhere and any terminal. The standard is planned in three releases with Release 1 addressing nomadicity and user controlled roaming based on use of an access network attachment subsystem and DSL/WLAN access methods; Release 2 optimizing resource usage according to user subscription profile and service use; while Release introduces full nomadicity and high-bandwidth access methods such as VDSL, FTTH and WiMAX. The TISPAN-based NGN architecture is shown in Figure 5. 978-3-8007-2909-8/05/$20.00 2005 IEEE 2291

B. End-to-end network architecture The end-to-end network architecture of Figure 6 shows a variety of 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 and firewall traversal of SIP flows for a) the DSL-based network (A-SBG), b) mobile networks (M-SBG) and 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. A fundamental issue for the end-to-end network architecture is traffic management and in particular how Quality of Service (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 network, or a WiMAX network. Network Processors play a vital role in order to accomplish this interworking function in a flexible and future-proof way, since customized ASIC design is probably very expensive in a world of continuously evolving standards. IV. CONVERGENT SERVICES AND TERMINALS A. Service 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, and different types of networks - cable TV, mobile or fixed line. As mentioned earlier, IMS, the standardized solution for Session Initiation Protocol (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 introduction of new services faster and easier. The common service execution environment of IMS supports user applications available over multiple accesses (access aware service platforms). There will be one common user and services management function, a common charging system, and a common identification and authorization system. Presence information is a key component for many IMSbased services. Presence-aware communication allows a user to see recipient information before connecting (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 and PC). Presence enables a paradigm shift in person-to-person communication. The majority of communication sessions using converged services, such as voice calls, video calls, chat sessions, file transfer, 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. B. Device Convergence Device evolution can be seen as a mirror of the core and access network evolution. It is in the device that the new applications will be available and the 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 Unlicensed Mobile Access (UMA), as described earlier. Storage requirements and capabilities will dramatically increase in both devices and networks. Some key network characteristics must also be available to devices connected to the fixed network. The evolution of connected home networks with various applications, such as interactive TV, games, music downloads, shopping and home security, to name a few, will require some of the characteristics that are delivered by IMS (e.g. quality of service, user management, charging and security) also in the fixed network and to stationary devices. Figure 7 shows some examples of devices connected to the home via a broadband connection that could benefit from network information, just like the mobile devices. V. CONCLUSIONS In this paper we surveyed the current situation in the standards area for fixed and mobile networks, discussed a variety of access alternatives for both networks and focus on the recent key developments that will enable fixed - mobile convergence in the future, namely the Unlicensed Mobile Access (UMA) initiative, currently repositioned as Generic Access Network (GAN) in 3GPP and the IP Multimedia Subsystem (IMS) architecture as defined in 3GPP R5 and R6 and 3GPP2 MMD specifications. We also discussed similar activities for Next Generation Networks (NGN) in ETSI TISPAN standardization activities and ITU NGN Focus Group. The target network architecture is then shown with numerous access methods and services built on top of IP Control intelligence. The role of IP-based traffic management as a vital component for the success of a multiservice and converged network is also mentioned. In particular the need for QoS mapping/interworking between different access networks and an IP core network is stressed. 978-3-8007-2909-8/05/$20.00 2005 IEEE 2292

REFERENCES [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] ETSI TR 00001 VO.3.0 TISPAN_NGN Release 1: Release Definition. [6] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley and E. Schooler. SIP: Session Initiation Protocol. LETF RFC 3261, June 2002. [7] ITU-T Recommendation G.992.5. Asymmetric Digital Subscriber Line (ADSL) transceivers - Extended bandwidth ADSL2 (ADSL2+). [8] A. Ghosh, D. Wolter, J. Andrews and R. Chen. Broadband Wireless Access with WiMAXI802. 16: Current Performance Benchmarks and Future Potential. IEEE Communications Magazine, February 2005. [9] 3GPP UTRA High Speed Downlink Packet Access (HSDPA). Overall Description. Stage 2. TS 25.308. [10] 3GPP2. Physical layer Standard for CDMA2000 Spread Spectrum Systems Release D. C.S0002-C VI CableLabs is a registered trademark of Cable Television Laboratories, Inc. WiMax is a trademark of Bandwidth.com, Inc. Wi-Fi is a registered trademark of Wireless Ethernet Compatibility Alliance, Inc. Bluetooth is a trademark of Bluetooth SIG, Inc., USA IEEE is a registered trademark of the Institute for Electrical and Electronics Engineers, Inc. 978-3-8007-2909-8/05/$20.00 2005 IEEE 2293

Figure 1: Fixed Mobile Convergence aspects 978-3-8007-2909-8/05/$20.00 2005 IEEE 2294

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