TCP/IP-based multimedia applications and services over satellite links: experience from an ASI/CNIT project

This article describes the activity performed in the three-year project “Integration of Multimedia Services on Heterogeneous Satellite Networks,” funded by the Italian Space Agency (ASI) and carried out by the Italian National Consortium for Telecommunications (CNIT). The description of the activity allows highlighting the problems, findings, and solutions in utilizing TCP/IP-based services and applications, such as audio-video transmission and Web browsing, via satellite channels. The article presents an experimental approach to provide QoS guarantees and to improve the performance of TCP over a satellite network based on the TCP/IP suite. The aim is to obtain a proper environment for data, voice, and video transmission oriented to a distance learning service that uses both audio-video applications and Web-based tools. The experimental scenario is made up of three remote LANs. Two of them are connected through a geostationary orbit satellite link in the Ka-band (20-30 GHz). The other LAN, located in a site where no satellite station is available, is connected through an ISDN link at 512 kb/s. Both subjective metrics such as mean opinion score and objective metrics such as throughput and overall transmission time have been used to evaluate the performance of the system and to get proper configurations able to guarantee a high QoS perceived by the users. The integrated services approach along with the resource reservation protocol were chosen to reserve the network resources at the IP level. A modified version of TCP has been proposed and utilized to reduce the download time during Web browsing and f.t.p. sessions. The measures reported have been obtained by real operative sessions