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Terminal Bridge Extension Over Distributed Architecture MSc. Sami Saalasti Agenda • • • • • • • Overview of Current Situation Service Distribution CORBA Wireless CORBA Terminal Bridge Extension Use-Cases Conclusions Overview of Current Situation • Wireless networks have become common varying from small Bluetooth networks to large-scale GSM networks • Combining different networks provides a situation where we can use “best features from every technology” • However, no general model for using these different wireless technologies together Service Distribution • Distributed Service Architecture describes a network environment which offers shared services to network users • Services can be distributed by using different approaches over CORBA or the Wireless CORBA • Both CORBA architectures can support several wireless networking technologies such as Bluetooth, WLAN and GPRS • The idea is to provide access to a shared service from different kinds of mobile networks CORBA 1/2 • Common Object Request Broker Architecture (CORBA), OMG's open architecture and infrastructure that computer applications use to work together over networks to perform remote invocations • Using the standard protocol Internet Inter-ORB Protocol (IIOP), vendor independent interoperability can be reached CORBA 2/2 • Network layer is completely hidden from applications, argument marshalling, connection handling, flow control handled by the Object Request Broker (ORB) • Underlying network must be reliable because no connection failures are expected Wireless CORBA 1/3 • New evolution of CORBA, the Wireless CORBA has been developed to specially operate on wireless networks • Wireless CORBA offers a software middleware solution for communication on several platforms with capability of performing flexible change of network access point (handoff) Wireless CORBA 2/3 • New components: Terminal Bridge (TB), Access Bridge (AB) and Home Location Agent (HLA) • Wireless CORBA utilizes centralized service model which provides one centralized service which can be accessed through several Access Bridges Home Location Agent Access Bridge Backbone network B Terminal Bridge Service wired link wireless link Access Bridge Wireless CORBA 3/3 • There may be multiple wireless networks available and the Wireless CORBA lacks methods to detect possible new networks if the current connection drops. • No implementation for monitoring the connection status • No implementation for handoff automation when connection weakens Terminal Bridge Extension 1/2 • Extension automates the handoff process and guards the connection state by monitoring signalling level • If the current connection seems to be too weak, the Terminal Bridge extension selects another available access point and commands Terminal Bridge to perform a handoff Terminal Bridge Extension 2/3 Terminal Bridge Extension 3/4 • Extension was used over the underlying Wireless CORBA architecture which was operating over TCP/IP (WLAN and GPRS) and L2CAP (Bluetooth) • The task of the extension was to guide the Terminal Bridge to select always the most suitable network Terminal Bridge Extension 4/4 Use-Cases 1/3 Use-Cases 2/3 Use-Cases 3/3 Conclusions 1/2 • Wireless CORBA and Terminal Bridge Extension provides very flexible architecture to use distributed services in changing wireless environment • Using very different wireless technologies together provides new possibilities for creating and using services Conclusions 2/2 • Currently, Bluetooth is problematic technology: inquiry and connection times can kill usability very effectively if user moves a lot from one network area to other • If plain Bluetooth network is used, it should be designed very precisely because one gap in the network coverage area breaks the link. • Better solution would be to use WLAN in the background and then decide what kind of Bluetooth network can be built • GPRS creates completely different possibilities to use services on a wider area because network coverage is no more as restricting factor