End-to-end QoS support for IP and multimedia traffic in heterogeneous mobile networks
Introduction
The number and variety of services of the second-generation wireless cellular (2G) systems have increased significantly in the past few years and this will continue to grow even further in the emerging third-generation (3G) and beyond (B3G) systems. Cellular services started with the basic voice communications and then several new data-oriented applications such as short-message service (SMS), electronic mail, WAP (wireless application protocol) for the web micro-browsing, and multimedia message service (MMS) have been gradually included. Design of advanced access technologies and core network architectures in 3G systems such as the Universal Mobile Telecommunication System (UMTS) and cdma2000 have resulted in higher data rates and more efficient spectrum utilization. This in consequence has made it possible that more bandwidth-demanding applications such as video conferencing and broadband Internet access will become available on a commercial basis to mobile users [1].
Introduction of new services into cellular networks has a two-fold characteristic. On one hand, in order to implement those services over the bandwidth-limited wireless channel, new access technologies and core network management techniques are required. Enhanced Data rates for Global Evolution (EDGE) for example has provided a better modulation to the 2G systems so that high data rates in order of 144, 384 Kbps, and up to 2 Mbps became feasible [1]. On the other hand, having new services in cellular networks logically means more interactions and interconnections among different telecommunications networks. In the first stages of the 2G implementations the main interconnection was with the public switching telephony network (PSTN). As shown in Fig. 1, in a 2G system mobile station (MSs) are connected to the PSTN mainly through two mobile entities: the base station subsystem (BSS) and the mobile switching center (MSC). Therefore, the simplified architecture of a 2G mobile system would mainly focus on support of air interface between the MS and the fixed telephony network.
Inclusion of more data-centric services in new mobile networks and the requirement of better support of those services need for more and better network interconnection options in compare with the 2G cellular systems. As a result, the enhanced 2G networks and their successor 3G systems look at architectures similar to the one shown in Fig. 2. In this configuration, the mobile system is connected not only to the circuit-switched telephony network for the purpose of voice communications but also to the data networks and especially to the global Internet for supporting web services.
Increase in more network interconnections and multimedia services has resulted in new challenges for cellular networks. In traditional cellular networks the main task was to make voice communications between a mobile station and a second party; another mobile station or a fixed telephone. In such a case, the problem was how to locate the geographic location of the mobile station when it makes or receives a call and then what will happen if the mobile station moves from the service area of one base station to another one while a call is in place. This latter issue is called handoff management and together with the former issue, namely the location management the mobility management problem is defined for cellular systems. Consequently, the quality of service (QoS) in original cellular networks was simplified by having a good mobility management control. Call dropping probability and signal-to-noise ratio (SNR) are therefore the main QoS metrics in such a network. When the number of mobile users is too high, then we need also to consider traffic management techniques in order to satisfy some other QoS metrics such as new call blocking probability and handoff call blocking probability when a user initiates a new call or when he moves from one cell to another cell during handoff, respectively.
With multimedia services and more network interconnections, support of QoS in cellular networks would not be straightforward anymore. Firstly, the multimedia services have diverse QoS requirements and supporting all those requirements to all services would be neither feasible nor essential at all times [2]. Some sorts of QoS management are thus necessary to achieve an acceptable level of service quality in future cellular networks. Secondly, because of the interconnection of heterogeneous networks in the system each with its own limitations, characteristics, and QoS handling techniques, achieving an end-to-end QoS is a real challenge. Without an end-to-end support of QoS in the system the issue will be unresolved.
In this paper, some challenging issues for the QoS support in wireless cellular systems will be addressed. We begin with a review of wireless Internet technology, and then in Section 3, QoS establishment in telecommunications networks will be revisited. This section describes requirements of an end-to-end QoS in heterogeneous networks and how this important issue needs to be considered in future mobile multimedia communication systems. After that, different approaches for cellular systems and the Internet QoS will be examined. The end-to-end QoS support in heterogeneous mobile networks with IP and multimedia traffic requires efficient collaborations among several networks involved in the end-to-end communications path. This issue has become a major topic in QoS guarantee in recent research (see e.g. [3]). In order to provide a practical example to clarify the issue, we will then present some specific numerical results on performance of the transmission control protocol (TCP), as the dominant transport layer protocol in wireless and cellular IP networks. This discussion looks at a new dimension to the TCP performance over cellular network compared with previous papers in the field.
Section snippets
The wireless Internet
The wireless mobile Internet, which was a dream just a few years ago, is now progressing so fast that it would revolutionize the whole framework of the telecommunication industry. The wireless mobile Internet is not just an extension of Internet into the mobile environment giving users access to the Internet services while they are on the move. It is about integrating the Internet and telecommunications technologies into a single system that covers all communications needs of human beings. With
Defining QoS in mobile multimedia networks
QoS is a terminology that has been around for quite some time and maybe it is one of the most common words that have been used by the people working in the field of telecommunications in the past few years. This usage popularity however, could not provide a clear definition of this important term and in some situations it has even led misunderstandings. The quality of service can be defined as a set of specific requirements for a particular service provided by a network to the subscribed users.
Techniques in supporting QoS
Another inconsistency can be discovered in the way the QoS support is approached in different network designs, including IP networks and 2G/3G networks. In the following, we will address those approaches. After that, we will discuss how this inconsistency makes the support of QoS to be challenging in future wireless multimedia networks.
TCP and QoS in heterogeneous networks
In this section, we focus our discussion on performance of the commonly used transport protocol, TCP, in wireless cellular multimedia IP networks. The performance of TCP over wireless channel has been addressed in many papers in the past few years and several techniques to improve the poor performance of TCP in mobile networks have already been proposed. In this paper, however, we want to illustrate that how a simple characteristic of the cellular network could cause major problems in providing
Conclusions
In this paper, some fundamental issues in supporting quality of service in future mobile multimedia and IP systems have been discussed. The QoS has been named in this paper as a term that should be looked on the basis of end-to-end. In future mobile networks where the transmission of multimedia and IP traffic is a mandate, then the end-to-end QoS has to be supported by all intermediate systems. Therefore, appropriate harmonization or mapping techniques are needed to be in place among the
Acknowledgements
The authors would like to thank Fei Xin for numerical results on TCP performance provided in the paper.
Abbas Jamalipour ([email protected]) is with the School of Electrical and Information Engineering at the University of Sydney, Australia, where he is responsible for teaching and research in wireless data communication networks, wireless IP networks, network security and cellular communications. He holds a PhD in Electrical Engineering from Nagoya University, Japan. He is the author of The Wireless Mobile Internet—Architectures, Protocols and Services, John Wiley & Sons 2003. In addition,
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Abbas Jamalipour ([email protected]) is with the School of Electrical and Information Engineering at the University of Sydney, Australia, where he is responsible for teaching and research in wireless data communication networks, wireless IP networks, network security and cellular communications. He holds a PhD in Electrical Engineering from Nagoya University, Japan. He is the author of The Wireless Mobile Internet—Architectures, Protocols and Services, John Wiley & Sons 2003. In addition, he has authored another book on satellite communication networks with Artech House in 1998, and coauthored three other technical books on wireless telecommunications. He has authored over 130 papers in major journals and international conferences. He has organized several special issues on the topic of 3G and beyond wireless cellular systems as well as broadband wireless networks in IEEE magazines and journals. He is a technical editor to the IEEE Wireless Communications Magazine, IEEE Communications Magazine, and the Wiley International Journal of Communication Systems. Professor Jamalipour is the Technical Program Vice-Chair of IEEE WCNC2005, Co-Chair of Symposium on Next Generation Networks for Universal Services, IEEE ICC2005, Technical Program Vice-Chair IEEE HPSR 2005, Technical Program Chair for the Wireless Communications Symposium, IEEE GLOBECOM2005, and Technical Program Co-Chair of Symposium on Next Generation Networks, IEEE ICC2006. He is a Fellow Member of IEAust; a Senior Member of IEEE; Chair of IEEE Communications Society Satellite and Space Communications Technical Committee; Vice Chair of Asia Pacific Board, Technical Affairs Committee; and Vice Chair of Communications Switching and Routing Technical Committee.
Pascal Lorenz ([email protected]) received a PhD degree from the University of Nancy, France. Between 1990 and 1995 he was a research engineer at WorldFIP Europe and at Alcatel-Alsthom. He is a Professor at the University of Haute-Alsace and responsible of the Network and Telecommunication Research Group. His research interests include QoS, wireless networks and high-speed networks. He was the Program and Organizing Chair of the IEEE ICATM'98, ICATM'99, ECUMN'00, ICN'01, ECUMN'02 and ICT'03, ICN'04 conferences and co-program chair of ICC'04. Since 2000, he is a Technical Editor of the IEEE Communications Magazine Editorial Board. He is the secretary of the IEEE ComSoc Communications Systems Integration and Modeling Technical Committee. He is senior member of the IEEE, member of many international program committees and he has served as a guest editor for a number of journals including Telecommunications Systems, IEEE Communications Magazine and LNCS. He has organized and chaired several technical sessions and gave tutorials at major international conferences. He is the author of three books and 135 international publications in journals and conferences.