Abstract
Idea of interworking, universal mobile telecommunication system and wireless local area network, to serve users with better quality of service, has bang with increase in demand for internet services, through third generation mobile networks. In this aspect, loose coupling, tight coupling and hybrid coupling architectures were proposed for interworking of the two networks. This paper analyses the performance of those interworking architectures through simulation, using OPNET14.5.
I. INTRODUCTION
Third-Generation Partnership Project (3GPP) has standardised Universal Mobile Telecommunications System (UMTS) which is a Third generation (3G) cellular system, as high-speed mobile telecommunications system that supports real-time and non-real-time multimedia services [1]. 3G cellular system will provide wide coverage and nearly universal roaming, but will not realistically live up to the bit rate expectations placed on them [2]. Successful deployment of wireless local area networks (WLANs) worldwide, which offer bit rates surpassing those of 3G systems, has yield a demand to integrate them with UMTS to develop heterogeneous mobile data networks, capable of supporting ubiquitous data services with very high data rates in hotspots [3]. Interoperability and interworking are key next generation network (NGN) concepts and it is required that all NGNs and components of an NGN be interoperable and that NGNs should be able to interoperate and interwork with other networks [4]. Many standardisation bodies, such as the 3GPP consortium, IETF, IEEE and ETSI are actively working on this issue and defining the basics for WLAN’UMTS integration. The study can still be considered at its infancy and a great deal of research and design activity is still required. Due to the complexity of the envisaged integration, it could be fulfilled by ‘interconnecting’, in a first stage and ‘completely integrating’, in a further evolutionary step, the WLAN technology and the 3G UMTS cellular systems [5]. Mobiles need to have dual interfaces in order to access both networks. In hotspots, mobile node (MN) uses WLAN access and outside of hotspots it uses UMTS [6]. The rest of the paper is organised as follows, section II elaborates interworking architectures, section III discusses contribution of this paper in simulation scenario, section IV discusses simulation results and section V concludes this paper.
II. INTERWORKING ARCHITECTURES
Several interworking architectures have been proposed in [7] to combine WLANs and cellular data networks into integrated wireless data environments. Two main architectures have been proposed [1-3], [5-8] for interworking between 802.11 WLAN and 3G cellular systems: (1) Tight coupling and (2) Loose coupling. When the loose coupling scheme is used, the WLAN is deployed as an access network complementary to the 3G cellular network. In this approach, the WLAN bypasses the core cellular networks and data traffic is routed more efficiently to and from the Internet without having to go over the cellular networks which could be a potential bottleneck as shown in Fig. 1a. However, this approach mandates the provisioning of special Authentication, Authorization and Accounting (AAA) servers on the cellular operator for interworking with WLANs’ AAA services. On the other hand, when the tight coupling scheme is used, the WLAN is connected to the cellular core network or radio network core (RNC) in the same manner as any other 3G Radio Access Network (RAN) or UMTS NodeB as shown in Fig. 1b, so that the mechanisms for mobility, quality of service (QoS) and security of the 3G core network such as UMTS can be reused. As a result, a more seamless handoff between cellular and WLAN networks can be expected in the tightly coupled case as compared to the same for the loosely coupled case [8]. Under the Tight coupled system, it is expected that WLAN users can also use UMTS services with guaranteed QoS and seamless mobility. However, the interworking is problematic. The capacity of UMTS core network nodes cannot accommodate the bulky data traffic from WLAN, since the core network nodes are designed to handle the small-sized data of circuit voice calls or short packets [9]. A hybrid coupling scheme proposed in [10], differentiates traffic paths according to the type of the traffic. For real-time traffic, the tightly coupled network architecture is chosen and for non-real time and bulky traffic, the loosely coupled network architecture is chosen. The network architecture for hybrid coupling scheme is shown in Fig. 1c. Hybrid coupling [11-13] scheme could accommodate traffic from WLAN efficiently with guaranteed QoS. In addition, it guarantees mobility and provides seamless service, just as does the tightly coupled scheme, while users are moving or need to change their access technologies.
Fig. 1 Interworking WLAN and UMTS networks coupled in various architectures.
III. SIMULATION SCENARIO
Mobile IP, Emulator and Gateway approach of interworking were analysed for their vertical hand off latency in [14], which are loose, tight and hybrid coupling architecture of interworking respectively, it is shown that tight and hybrid coupling has similar and better performance than loose coupling architecture in terms of vertical hand off latency. Other QoS metrics of those architectures were not analysed. This paper analyses and evaluates them through simulation using OPNET 14.5 and their performances in terms of load handled by a network in interworking, media access delay [],
Table I. Simulation parameters
S. No. Parameter Value
1. No. of users in WLAN & UMTS 100
2. FTP File size 50000 bytes
3. FTP inter request time 360 sec.
4. Simulation duration 900 sec.
5. Voice Spurt & Silence length in both incoming and outgoing 35% & 65%
Fig. 2 Scenario of loosely coupled architecture
Fig. 3 Scenario of tightly coupled architecture
Fig. 4 Scenario of hybrid coupled architecture
IV. SIMULATION RESULTS
Fig. 5 Wireless LAN load
Fig. 6 Wireless LAN Media Access delay
Fig. 7 Voice application packet delay variation
Fig. 8 Voice application traffic sent
Fig. 9 Delay
Fig. 10 UMTS throughput
V. CONCLUSION
High hand over latency of loose coupling has paved way for tight coupling. Packet loss for heavy data in tight coupling decreases throughput that paves way for hybrid coupling. Though hybrid coupling is proposed as an alternate to tight coupling, it provides only moderate throughput. It is observed from simulation results that media access delay in hybrid coupling is high, compared to other schemes. Research has to be carried towards minimization of media access delay in hybrid coupling architecture.
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15.
R. Shankar received Bachelor of Engineering in 2001 and Master of Technology in 2006 in Electronics and Communication Engineering (ECE) from Bharathidasan University, Trichy and Pondicherry Engineering College, Pondicherry, India respectively. He is pursuing his Ph.D. in the Department of ECE, Pondicherry University. He is currently working as Assistant Professor in the Department of ECE at Sri Manakula Vinayagar Engineering College Pondicherry, India. His research interests include wireless communication, computer networks and convergence network.
P. Dananjayan received Bachelor of Science from University of Madras in 1979, Bachelor of Technology in 1982 and Master of Engineering in 1984 from Madras Institute of Technology, Chennai and Ph.D. degree from Anna University, Chennai in 1998. He is working as a Professor and Chairman in the department of ECE and CBCS respectively in Pondicherry Engineering College, India. He also has been as visiting Professor to Asian Institute of Technology, Thailand. He has more than 100 publications in National and International Journals. He has presented more than 150 papers in National and International conferences. He has guided 11 Ph.D candidates and is currently guiding 6 Ph.D students. His areas of interest include spread spectrum techniques and wireless communication, wireless adhoc and sensor networks.