Nov 6, 2005 - infrastructures is the Moby Dick project [7]. This project develops, implements and evaluates IPv6- based mobility-enabled network architecture ...
Providing Interoperability in Heterogeneous Environments towards 4G Liljana Gavrilovska, Vladimir Atanasovski, Valentin Rakovic, Ognen Ognenoski, Aleksandar Momiroski Faculty of Electrical Engineering and Information Technologies, Karpos 2 bb, 1000 Skopje, Macedonia E-mail: {liljana, vladimir}@feit.ukim.edu.mk
Abstract – Constant development of wireless and mobile networks and their capabilities enlarges the plethora of possible user services. It opens potentials for the operators to increase their service portfolio and for the users to experience context-rich and personalized services. In this manner, the interoperability between different wireless networks and the enabling of seamless Vertical Handovers (VHOs) become crucial cornerstones in the development towards a fully integrated 4G all-IP network architecture. This paper explores the development towards 4G exploring the benefits of the interoperability issues in heterogeneous networks and elaborating on the emerging IEEE 802.21 standard. Keywords - Interoperability, 4G, Vertical handover, IEEE 802.21 1. INTRODUCTION: TOWARDS 4G
2. BENEFITS OF INTEROPERABILITY
The need for pervasive and ubiquitous networking requires integration of various wireless solutions (e.g. 3G and beyond, WiMAX, WiFi), each with own inherent characteristics, into a single platform capable of supporting transparent and seamless user roaming. The process is additionally followed by the development of new user devices designed to deal with the various network platforms and protocols. The Fourth Generation of communications systems (shortly 4G) [1] is all about a global wireless communications system and defines a cost effective, simple, operable and personalized according to the users’ needs concept. It is an open, all-IP based, seamless connectivity system foreseen as an integrator among all existing, planned and future wireless and wired networks. 4G’s major goals are integration and convergence. The former should offer seamless interoperability of different types of wireless networks with the wireline backbone. The latter relates to the convergence of different traffic types (e.g. voice, multimedia and data) over a single IPbased core network, different technologies (e.g. computers, consumer electronics and communication technology), different media (e.g. broadcast, satellite, cellular), different services etc. This paper explores the aspects of interoperability towards 4G [2] and the emerging IEEE 802.21 technology [3], concepts targeted within an ongoing research project RIWCoS [4]. Section 2 discusses the benefits of the interoperability and the related work prior to the IEEE 802.21 framework. Section 3 elaborates the IEEE 802.21 standard, shows the major technical ideas of the RIWCoS paradigm and presents some preliminary simulation results obtained within the RIWCoS project. Finally, section 4 concludes the paper.
The rapid development of various wireless communications systems worldwide and, in the same time, the rapid changes in users’ profiles and market needs yield the necessity of interoperability. It will bring benefits from both the network providers’ perspective and the users’ perspective and contribute to the robustness of the provisioning of users’ requested services, while at the same time allow user seamless and transparent service management. At the network level, the reconfigurable interoperability will offer network providers with a possibility to choose, with minimal investments, between alternative wireless access networks. The selection could be made based on several criteria such as comparison between the availability of access resources and specific service requirements (e.g. channel state, outage probability, vertical handover probability, users’ QoS requirements, context awareness etc.), load sharing and distribution between different spatially coexisting wireless networks, efficient spectrum sharing, preferred gateway selection and network discovery, congestion control etc. Thus, any changes in the network resource availability due to network instantaneous saturation or equipment crashes can be bypassed by terminals and network components that are dynamically adapted to the new situation. This will lead to more vibrant market movement and increased users’ choices. At the user level, the interoperability of the heterogeneous 4G system will lead to more efficient end-to-end connectivity and service delivery in heterogeneous environments, easier worldwide roaming and dynamic adaptation to regional contexts, enhanced personalization and richer services. The users’ devices will reconfigure based on available resource usage capabilities (the
information will be provided by navigation and/or localization systems), spectral agility capabilities and the level of cognitism they posses, minimization of the service cost when multiple underlying technologies are available, anticipation of user contexts and preferences. There are several attempts found in the literature to practically deploy a heterogeneous interoperable environment. One of the first successful experimental testbed efforts is the LCE-CL testbed [5, 6] consisted of a loosely-coupled, Mobile IPv6 (MIPv6)-based GPRS/WLAN/LAN heterogeneous network. The results show that the MIPv6 protocol is designed only for mobility management within the same technology. When dealing with VHOs, MIPv6 yields the latency to exceed acceptable limits (realtime applications cannot be supported). Another integrated architecture that continues the evolution of the 3rd generation mobile and wireless infrastructures is the Moby Dick project [7]. This project develops, implements and evaluates IPv6based mobility-enabled network architecture with Authentication, Authorization, Accounting and Charging (AAAC) services and support for Quality of Service (QoS). A representative set of interactive and distributed multimedia applications is used to derive the system requirements for verification, validation, and demonstration of the integrated architecture in a testbed comprising different access technologies: WCDMA, IEEE 802.11 and Ethernet. The Service Oriented Handover (SOHand) platform [8] tries to create proper conditions to exploit the split of VHOs in downward (when the handover allows for a decrease of bandwidth) and upward (when the new bandwidth opportunity is larger). It adds to the handover process the awareness of the ecosystem in which the event is embedded. The basis of the system is a versatile information structure (an ontology), which could be shared by the providers and users. The ontology is the unifying technology, providing a common understanding of the terms and relationships which could be jointly maintained by the providers. 3. IEEE 802.11 FRAMEWORK This section elaborates on the emerging IEEE 802.21 technology. It describes the IEEE 802.21 standard, presents the major technical objectives of the RIWCoS project and shows some preliminary simulation results on the VHO latency performance. 3.1. The IEEE 802.21 standard The IEEE 802.21 standard facilitates the handover between different wireless networks in heterogeneous environments regardless of the type of medium. The standard names this handover as Media Independent Handover (MIH). The goal of
IEEE 802.21 is to better and ease the mobile nodes’ usage by providing uninterrupted handover in heterogeneous networks. For this purpose, the handover procedures can use the information gathered from both the mobile terminal and the network infrastructure. The heart of the 802.21 framework is the Media Independent Handover Function (MIHF), Fig. 1. The MIHF will have to be implemented in every IEEE 802.21 compatible device and will be responsible for communication with different terminals, networks and remote MIHFs providing abstract services to the higher layers using a unified interface (L2.5 functionalities). MIHF defines three different services: Media Independent Event Service (MIES), Media Independent Command Service (MICS) and Media Independent Information Service (MIIS). MIES provides events triggered by changes in the link characteristic and status. MICS provides the MIH user necessary commands to manage and control the link behavior to accomplish handover functions. MIIS provides information about the neighboring networks and their capabilities.
Fig. 1. IEEE 802.21 architecture The IEEE 802.21 standard is still in its formative stages. However, the interest that exist both in academia and industry shows that it may be the key enabler for seamless handovers and transparent roaming in heterogeneous networks. Related work in the field may be found in [9-14], where the IEEE 802.21 framework was used to deliver lower VHO disconnection times, QoS based VHO, cross-layer based VHO and provide assistance to mobility management, respectively. It is clear that the IEEE 802.21 technology will make a major contribution towards the reconfigurable interoperability aspect of future generation wireless communications systems. 3.2. The RIWCoS paradigm The RIWCoS (Reconfigurable Interoperability of Wireless Communications Systems) project [4] contributes the development towards 4G by creating a solution compatible with the IEEE 802.21 standard and able to exploit the synergy between various wireless access technologies. The overall RIWCoS architecture is shown in Fig. 2.
GW = Gateway IM = Interoperability Module RM = Resource Management System Module = Data Link = Resource Management Signaling
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different CBR/UDP traffic bit rates. The handover latency is defined as the time difference between the moment the MN detects the coverage of another wireless technology (LINK DETECTED trigger in the IEEE 802.21 framework) and the receive of an acknowledgement packet from the CN. This acknowledgement packet assures the MN that the traffic flow is being redirected to the second interface.
Fig. 2. The overall RIWCoS architecture [4] RIWCoS will implement and demonstrate an open, secure, fast-reconfigurable and “easy to use” IEEE 802.21 based content delivery platform that will be used for high quality multimedia services (transport and distribution), through any type of wireless access networks to mobile and residential end-users. The project specific goal is to define a flexible architecture for a service delivery platform that manages a reliable data content distribution through any wireless access networks to mobile and residential end-users, as well as develop service scenarios for data content distribution. In addition, the RIWCoS project will define, develop and implement a resource management system for a heterogeneous communication network. Finally, the project will execute real-time experiments to demonstrate the functionalities of the system. The RIWCoS project started in 2007 and will end in 2010. 3.3. Preliminary simulation analysis This subsection shows preliminary simulation analysis, done within the RIWCoS project, of the VHO performance utilizing IEEE 802.21. The simulations are performed with the ns-2 [15] simulator, along with NIST’s seamless mobility package [16] extensions. A parameter of interest is the experienced handover latency, which gives clear insight into the handover behavior in heterogeneous environments (in terms of whether the user traffic can tolerate the latency or not). Analyzed simulation scenario investigates handover effects between UMTS, IEEE 802.16 (WiMAX) and IEEE 802.11 (WiFi) networks. It consists of a Corresponding Node (CN) generating traffic towards a Mobile Node (MN), 2 intermediate routers, IEEE 802.11 Access Point (AP), IEEE 802.16 Base Station (BS) and a UMTS Node B placed in a simulated area of 2000m x 2000m. The whole simulation area has UMTS coverage, whereas the IEEE 802.16 and the IEEE 802.11 technologies cover a circular area with a radius of 500m and 40m inside, respectively. The MN moves freely throughout the simulation area performing various VHOs. The assumed channel model is ideal. Fig. 3 shows the dependence of the UMTS -> WiMAX handover latency on the MN’s speed for
Fig. 3. Handover latency vs. node speed The handover latency increases with the MN’s speed increase because of the definition of the latency as a background process that starts from the moment the MN “senses” the new technology till the first acknowledgment packet is received through the newly activated interface. However, it is important to stress that the MN’s connection with the CN will be continuous and will not require to be reset during the actual VHO. This is owed to the IEEE 802.21 technology, which seamlessly prepares the interfaces at the MN for the VHO. The curves for different bit rates overlap due to the simulation scenario setup, i.e. there are only high capacity (100 Mbps) links in the wired part of the topology setup. Fig. 4 and 5 depict the handover latencies vs. node speed for UMTS -> WiFi and WiMAX -> WiFi VHOs. Comparing to Fig. 3, it is evident that these two VHOs exhibit much smaller latencies. This result provides crucial benefits for operators having different Radio Access Technologies (RATs) deployed. Users moving from a typical higher coverage RAT (i.e. UMTS or WiMAX) to a lower coverage RAT (i.e. WiFi) can be seamlessly and transparently switched. This allows for user transparent load sharing between various RATs and/or user transparent switch to an alternative and preferable (e.g. cheaper) RAT.
Fig. 4. Handover latency vs. node speed for UMTS > WiFi case
Fig. 5. Handover latency vs. node speed WiMAX -> WiFi case This section explored the characteristics of the emerging IEEE 802.21 framework and presented the related RIWCoS project. Even though the simulation results are merely preliminary, they clearly show the potentials of the IEEE 802.21 technology for providing interoperability towards 4G and prove the justification of the RIWCoS paradigm. 5. CONCLUSION Future wireless communications systems are envisioned to offer higher data rates, higher mobility support and seamless communication [17]. They will have to utilize a common platform that will unify a variety of evolving access technologies, seamless interworking and interoperability solutions and adaptive multimode user terminals [18]. This paper elaborated the interoperability issue towards 4G development. It explored the lately emerging IEEE 802.21 standard for seamless VHOs, discussed an ongoing research project, RIWCoS, and provided a preliminary simulation analysis of the major contributions of the IEEE 802.21 framework. The results showed that the IEEE 802.21 allows for low VHO latencies yielding more consistent, seamless and transparent VHO. ACKNOWLEDGEMENT This research is sponsored by the NATO SfP982469 "Reconfigurable Interoperability of Wireless Communications Systems (RIWCoS)" project. The authors would like to thank everyone involved. REFERENCES [1] R. Tafazolli (ed.), Technologies for the Wireless Future: Wireless World Research Forum, John Wiley and Sons, 2006. [2] L. Gavrilovska, V. Atanasovski, “Interoperability in Future Wireless Communications Systems: A Roadmap to 4G,” Microwave Review, 13(1), June 2007, pp.19 - 28. [3] IEEE 802.21: Media Independent Handover, URL: http://www.ieee802.org/21
[4] NATO SfP-982469 RIWCoS (Reconfigurable Interoperability of Wireless Communications Systems) project, 2007-2010. URL: http://riwcos.comm.pub.ro/ [5] P. Vidales, “Seamless mobility in 4G systems,” Technical report 656, University of Cambridge, November 2005. [6] P. Vidales et al, “A practical approach for 4G systems: deployment of overlay networks,” TRIDENTCOM 2005, February 2005. [7] IST-2000-25394 Moby Dick (Mobility and Differentiated Services in a Future IP Network) project. URL: http://www.ist-mobydick.org/ [8] Project: “SOHand: an ontology-based platform for building services to exploit contextual handovers information”. 2007-2010. URL: http://www.sohand.icmc.usp.br/ [9] A. Dutta et al., “Seamless Handover across Heterogeneous Networks – An IEEE 802.21 Centric Approach,” WPMC 2005, Aalborg, Denmark, September 2005. [10] Project: “QoS based vertical handoff between WLAN and WiMAX compatible with the IEEE 802.21 framework”. Queen Mary, University of London. URL: http://www.elec.qmul.ac.uk/networks/opnet.ht ml [11] N. Golmie and S. Woon, “Performance Measurement for Link Going Down Trigger,” IEEE 802.21 session #11, Vancouver, Canada, date submitted: November 6, 2005. [12] T. Melia et al., ”Impact of heterogeneous network controlled handovers on multi-mode mobile device design,” IEEE WCNC 2007, Hong Kong, March 2007. [13] Y. Ohba, “Seamless and Secure Handover for Heterogeneous Mobility using PANA, IEEE 802.21 and Pre-authentication,” B3G Cluster Workshop on Mobility Technologies in the Internet, Brussels, Belgium, October 2006. [14] Q. B. Mussabir et al., “Optimized FMIPv6 using IEEE 802.21 MIH Services in Vehicular Networks,” IEEE Transactions on Vehicular Technology, November 2007. [15] The Network Simulator – ns-2. URL: http://www.isi.edu/nsnam/ns/ [16] NIST Seamless and Secure Mobility project. URL: w3.antd.nist.gov/seamlessandsecure.shtml [17] L. Gavrilovska, R. Prasad, Ad hoc networking towards seamless communications, Springer, 2006. [18] B. Walke, IEEE 802 Systems: Protocols, Multihop mesh/relaying, Performance and Spectrum Coexistence, John Wiley and Sons, January 2007.
