Interoperability and Testing in Broadband Satellite Networks
Abbasi, Munir1; Stergioulas, Lampros1; El-Haddadeh, Ramzi1; Kretschmer, Mathias2; Pitsilis, Vassilis3; Tsiolis, I.4; Zagkos, D.4; Hatziefremidis, A.4
1School of Information Systems, Computing and Mathematics, Brunel University; 2Fraunhofer Gesellschaft zur Foerderung der angewandten Forschung e.V., DE; 3National Center for Scientific Research “Demokritos”, GR; 4Hellenic Aviation Industry S.A., GR
By combining satellite and terrestrial (wireless) technologies, full coverage and high capacity can be achieved for true broadband services. The interoperability of such diverse networks imposes a number of challenges regarding service provision and management. The end-to-end quality of service management implies that features such as service scalability between different networks have to be available. On the other hand, wireless QoS requirements provide a promising diversity for a wide range of seamless applications. However, differences in QoS properties between both wired and wireless applications have a considerable effect on the quality level as well as platform and application dimensions of network interoperability. This paper examines the so-called interoperability requirements in integrated uses of satellite communication technology together with terrestrial network (wireless) technology for seamless delivery of the services (using ISABEL and CLIX e-learning applications) in rural and remote areas. This is demonstrated with an example of an educational service.
Introduction:
The aim of this paper is to establish the so-called interoperability requirements in integrated uses of satellite communication technology together with terrestrial network (wireless) technology for seamless delivery of the services. This is demonstrated with an example of a satellite-enabled educational service in rural and remote areas (using ISABEL and CLIX e-learning applications) under the BASE2 EU project. The implemented hybrid broadband network is tested with the aim to identify the interoperability issues and the main challenges in the development and operation of heterogeneous satellite-terrestrial networks. The focus is to ensure that the combined wireless technologies meet the network requirements of demanding real-life applications.
Interoperability in Hybrid Networks: Testing Different Link Configurations and Architectures
The testbed of this study is the network developed in the BASE2 EU project, which designed and deployed a hybrid, satellite- and wireless-based network infrastructure, and learning services to support distance learning for geographically isolated communities. BASE2 focuses on the empowerment (enabling learning) for members of the agrarian or maritime isolated communities. The BASE2 project involves the deployment of the service and network infrastructure and a number of trials. 10 agrarian community sites in Greece and 2 in Cyprus are now active with full network and service deployment. A number of different network testing scenarios have been carried out. These tests aim to study connectivity-related issues for the various architectural scenarios of BASE€ link configurations. This includes Satellite only, Satellite and WiMax and finally Satellite, WiMax and WiFi as shown in Fig. 1 below.
Figure 1 - Test Bed Infrastructure
The four test machines located close to the HUB station, the VSAT terminal and the intermediate WiMax/WiFi nodes are connected to the Inter/Intra-net via a separate interface so that no extra management traffic influences the satellite/WiMax/WiFi link measurements.
Results:
Extensive tests have been obtained in order to assess the performance of the BASE 2 network infrastructure, in meeting the requirements of the offered applications. Interoperability requirements of such networks as well as methodological issues and best practice (lessons learned) in testing of hybrid networks are discussed. P> Conclusions:
Terrestrial services, like WiMax IEEE802.16 can transport and deliver IP data symmetrically in both directions. Round trip time is around 40 - 60 ms between sector controller and subscriber station. The maximum throughput is around 23 Mbps in both directions, i.e. channel size does not matter with regards to broadband channel requirements.
Satellite services, as DVB-RCS, do have a substantial round trip time of approximately 640 to 680 ms due to speed of light when communicating over the geostationary satellite Hellas-Sat 2 on 39 degrees East. Since RCS is a highly asymmetric service (large Mbps-sized bandwidth on downlink and some tens or hundreds of kbps throughput on the individual uplink) broadband requirements can be met when delivering through downlink towards the target area. Additionally, by introducing a clever traffic prioritization and carrier management on the return channel, the jitter of the round trip time has been minimized and throughput numbers have been optimized at the same time.
Finally, a synoptic review of testing strategies and methods, suitable for interoperability testing of hybrid networks is presented, based on the findings of the network testing performed on the BASE 2 network.
Acknowledgments
The authors gratefully acknowledge that this presented work is supported by the Aeronautics and Space programme of the European Commission, as part of the BASE2 project (Contract no.: 516159)