Solution for Implementing IEEE 802.21 Media Independent Information Service Valentin Andrei
Eduard C. Popovici, Octavian Fratu, Simona V. Halunga
Research & Development Department SOFTWIN Bucharest, Romania
[email protected]
Telecommunication Department ETTI Faculty, Politehnica University of Bucharest Bucharest, Romania
[email protected],
[email protected],
[email protected]
By properly configuring the MIIS, one user can optimize his handovers by choosing the best networks with the best connectivity and also taking account of the amount he is willing to pay for the services. As we can see, the MIIS is a global database storing all the information needed for providing the user the best handover experience. This database needs also to be accessible by browsing the Internet by regular users. The main problem that arises is how this entity could be implemented with the ability of providing a response in a short amount of time.
Abstract—This paper describes a solution for implementing the Media Independent Information Service, later referred to as MIIS, described in IEEE 802.21 standard. First we present the previous work towards defining a complete system capable of realizing a vertical handover according to the standard. Next we detail the MIIS general architecture, the information gathering procedures and considerations about the data format used in communicating. The last section presents a typical usage scenario and the advantages of implementing MIIS. Keywords - vertical handover; heterogenous network; IEEE 802.21; information service
I.
In section II we present our previous work related to the IEEE 802.21 standard components. Sections III, IV and V are dedicated to the new proposed architecture and details of our solution, while the Section VI presents a possible scenario for the whole system usage. The last section concludes the paper.
INTRODUCTION
Realizing an independent vertical handover in a heterogeneous network has been the goal of many telecommunications researchers and engineers in the last few years. The advantages achieved by completing this objective can be numerous. For example, being able to switch seamless between the access technologies, one could keep his communication session even if one or more links fall down. This feature is very important in case of natural calamities like earthquakes, fires, etc. The mobility of a wireless device would increase exponentially, by not depending of a single access technology.
II.
PREVIOUS WORK
During the past two years we focused our research towards defining and implementing a prototype for a system capable of performing an independent vertical handover, according to the IEEE 802.21 standard. Fig. 1 represents a high level representation of the components of our system.
The ability to switch the connection from one technology to another one keeps getting closer in the last years. The IEEE 802.21 standard, [5], describes a set of components that linked together will provide a mechanism capable of completing a vertical handover, on a mobile device. The main challenge in implementing the standard is to build software capable to unify all the communication technologies in a single protocol, with minimum changes in the existing infrastructure [6] [7]. So, basically the new software will act like a wrapper enclosing all the methods of accessing a network device. One of the standard’s components is the Media Independent Information Service (MIIS). Its role is to provide information about wireless access points (AP) located inside the terminal’s coverage area. This information could vary from connectivity parameters, like the MAC address, channel range, signal strength to billing policies, security principles, etc.
c 978-1-4244-6363-3/10/$26.00 2010 IEEE
Figure 1. General architecture of RIWCoS system
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The key component of the system is the Interoperability Manager (IM). It provides an unified interface to all the access technologies, situated in the control plane between L2 and L3. This component has its general architecture defined in [3] and explained in detail in [2]. The switching between connections is realized inside this block, by simply changing the active protocol stacks, for example from 802.11 to 3G. The Media Independent Handover (MIH) Protocol is the heart of the system, interconnecting all the entities of the system. The Information Server provides records about all the networks located inside the mobile terminal coverage area. Based on the data sent by this component, the device can take a decision on which link to move the connection. This Information Server represents the MIIS entity described in IEEE 802.21 standard. It is a complex sub-system that needs to store data from all the access points situated around the globe. So by sending its global coordinates as parameters, the mobile terminal must receive connectivity parameters and policies from all the hot spots situated in his coverage area. Based on this information a handover decision can be taken. The communication with the MIIS can be made via layer 2, but it would be more appropriate to communicate using a higher layer, since the mechanism for deciding which connection to choose is more complicated. Figure 2. MIIS topology
Efficiently implementing MIIS in a fully functional system involves the presence of several databases containing information about all the access points worldwide. Each database will contain records about all the hot spots located within the maximum coverage area of the server’s home network. This is why a central point is needed to store all the information, gathered from around the globe, and broadcast the changes in the network topologies, to all nodes.
If the mobile terminal switches from one network to another, then the information about new reachable AP, will be given by the Information Server (IS) of the visited network. The following Message Sequence Chart (MSC), shown in Fig. 3, displays a usage scenario involving the components of this system. When a new AP connected to the visited network is configured a report to the “Central Location” is generated. After the update interval expires, the node broadcasts the changes to all connected information servers, and this is how the home network IS updates its data.
An important feature for the MIIS system, is to give users the possibility of discovering the access points and their parameters by browsing the Internet. For this reason we suggest implementing a web application that connects to the central point’s database, and displays all the active access points according to geographical position. This feature would be helpful for the user, in order to define the succession of handovers for an established route. For example if one decides to take the train from one city to another, he can browse for the active access points that he encounters in his way, and he can configure his terminal to switch only to the most convenient networks. Of course, in order to realize that, the mobile device software must allow this configuration. III.
GENERAL ARCHITECTURE
Fig. 2 describes the structure of the MIIS distributed database. Every Information Server, hosted by some operator, needs to contain records about his own access points but also about access points located in the maximal area defined by his network. This is because the goal is not to limit the user to a single network, but to give him the possibility to choose its most convenient networks. A proper law policy needs to be applied in order to prevent large operators to obtain monopoly.
Figure 3. MIIS components interaction
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The mobile terminal briefly discovers active AP’s in its area and compares the data with those extracted from the information server. If some preferred networks are defined by the device software, the handover will occur towards those networks. If not, the decision will be taken based on connectivity parameters like signal strength, the coverage area radius, bandwidth, etc. At some point, a new access point may be configured within a network. At that moment, he will report to the information server hosted by that network, his coordinates and the provided connectivity parameters. The update will reach the “Central Location”, which must broadcast the changes in topology to every network whose maximum coverage area intersects with the initial network’s coverage area. IV.
CENTRAL NODE
As seen from the presented architecture, the “Central Location”, referred as “central node” from now on, is the “Brain” of the entire system. Its role is to coordinate all the Information Servers, and to make sure their information is updated. To ensure that, a permanent link must be kept between the information servers and the central node. This link can be established at higher layers, for example through a secure web-service. A web application is also needed in order to provide worldwide users, access to the known access points, and to allow them to configure their terminal for a certain route. The database stored at this central point must be properly designed, in order to efficiently broadcast the changes that occur at a certain point, to all the networks containing that point. An overview of the central node architecture is described in Fig. 4.
Figure 4. Central node components
These containers are the following:
The “Update Web-Service” is used by local information servers to notify the global database when the changes in topology will occur. At that point, the central node sends a message to all the information servers located near the changed network. When the servers receive the message, they launch a request to the “Broadcast Changes” Web-Service, and they extract the new recorded access point.
IE_CONTAINER_LIST_OF_NETWORKS
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IE_CONTAINER_NETWORK
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IE_CONTAINER_POA
Each component of the container will be composed of several information elements. For the network container, these elements will be for example the network type, the operator identifier, the service provider and information elements defining the characteristics of the network like the cost, the QoS, the data rate and the channel range.
The administration portal will be used to maintain the world-wide database, to make sure the users have the correct application versions, to erase old recordings, etc. It can be implemented as a web application so the administrators can operate the database remotely, using proper security mechanism, or at the central node’s headquarter. The visitors will be able to get the access points at any geographical coordinate by using the provided web application. The site will also contain software to be installed on the mobile device, in order to properly configure the successions of vertical handovers. V.
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For the Point of Access (PoA) container, information elements will link the entity to the owner network and will specify the most important parameters, like the channel range, the MAC address and the geographical position and the coverage area in global coordinates. The IS hosted by each network will have the task of packing the data according to the established format. It is recommended to design the database as closely to the standard as possible, in order to provide a short response time for each query.
DATA FORMAT
In [1], two methods for retrieving the information elements are presented. A simulation environment was built in order to test the Type-Length-Value (TLV) encoding, and the RDF/XML (Extensible Markup Language) transmission method. As demonstrated, the TLV method is the fastest and will provide the best results when a handover decision needs to
An important task in order to accomplish the MIIS, according to the IEEE 802.21 standard, is to establish the format of the data structures to be transmitted to the mobile device, at the scanning period. The standard defines a set of containers to be considered when transmitting the information to the terminal.
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policies defined previously, and if these networks are not present, the device will switch to the best network according to the implicit rules.
be made in a short time. The XML method can be used for entities with a higher processing power, for example when implementing the communication between the central node and the information servers on every network.
If the user does not have time to visit the web application of the central node, the handover decisions will be taken by considering some default settings or pre-configured ones based on optimization criteria, like cost, bandwidth, coverage area, etc.
However the usage of RDF/XML, is not a bottleneck for a mobile device since the requests to the web-service are not made very often, and the exchanged data amount is less than a few kilobytes, which is less than 10 seconds of speech. If hosted on a powerful server, the web-service can respond to more than 100 requests per second. Besides that, the data transfer is not to be made with the purpose of a handover decision and must be realized before that. VI.
CONCLUSION In this article, we proposed a general method of implementing the Media Independent Information Service, as a crucial part of a system fully capable of performing vertical handover, according to IEEE 802.21 standard. We presented the general architecture of the component, its functionality, some considerations on data formatting and a typical usage scenario. We demonstrated that by implementing efficiently the MIIS, the user can successfully optimize the mobile device, to switch to the preferred networks, according to his will.
USAGE SCENARIO
A typical usage scenario is suggested by the Fig. 5. The colored figures represent some networks coverage area, intersected, as disposed in territory.
ACKNOWLEDGMENT This work is sponsored by NATO's Public Diplomacy Division in the framework of “Science for Peace” through the SfP-982469 "Reconfigurable Interoperability of Wireless Communications Systems (RIWCoS)" project and by Romanian Authority of Scientific Research in the framework of PNCDI 2 “Partnership” through the 12-126/2008 “Hybrid wireless access system with unique addressing (SAWHAU)” project. REFERENCES [1] Figure 5. Typical usage scenario involving MIIS
The steps the user of the mobile device should follow, in order to optimize the successions of handovers are the following: •
[2]
Visit the central node web application, and extract the access points within his route.
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Download or update an application for the terminal, allowing him to define a list of preferred networks.
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Choose a list of preferred networks according to the characteristics presented on the web-site.
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Configure his mobile device using the downloaded application.
[3]
[4]
[5]
When the device moves from Start to Finish, he will choose the networks from the preferred list, for example N1 and N3. The terminal will communicate with the IS from the current visited network and will extract the nearby hot spots. If some of those belong to a network within the preferred list, the handover decision will be taken towards the preferred hot spots. He will switch to N1 and N3, no matter the handover
[6] [7]
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C. Antohe, “Practical approach of implementing Media Independent Information Service of IEEE 802.21 standard”, 1st International Conference on Wireless Communications, Vehicular Technology, Information Theory and Aerospace and Electronic systems technology, VITAE, 17-19 May 2009, Aalborg, Denmark E. C. Popovici, V. Andrei, O. Fratu, “Real-Time monitoring design of wireless network devices for vertcal handover on multimod terminals”, Proc. Of 2nd International Conference on Applied Sciences in Biomedical and Communications Technologies ISABEL Conference, 24 november, 2009 V. Andrei, E. C. Popovici, O. Fratu, S. Halunga „The architecture of a software module, supporting vertical handover in heterogenous networks”, Proc. of International Conference on Science ETAI Conference, 26-29 September 2009, Ohrid Macedonia O. Fratu, E. C. Popovici, S. V. Halunga, E. Stănescu, “Consideration on Interoperability of Different Wireless Access Networks using the IEEE 802.21 Approach”, accepted for International Conference TELSIKS ’09, Niš, Serbia, Oct 7 - 9, 2009 “IEEE Draft Standard for Local and Metropolitan Area Networks: Media Independent Handover Services”, IEEE P802.21/D9.0, February 2009 L. Jyh Chen, T. Sun, M. Gerla, “USHA: A practical seamless vertical handoff solution”, July 2005, Mobiquituos, San Diego, USA V. Kesavan, Intel, “WiFi/WiMAX Heterogenous Seamless Handover Demo”, February 2008, Mobile World Congress, Barcelona, http://blogs.intel.com/research/2008/02/wifi_wimax_handover.php
