Modem Satellite Networks based upon the Digital Video Broadcasting (DVB)/MPEG-2 Standards operating on a fixed bandwidth per transponder offer two service classes. For handling of the VideolAudio data stream either a constant or variable bit rate is required. In general the entire transponder bandwidth is not used for Video/Audio services, thus data services e.g. giving the user access to intemetlwWW can be added. For the i n t e m e m access either a data carousel or an inter-LAN data transfer based upon a TCP transparent communication or a mixture of both can be implemented. This paper presents an in depth throughput analysis of a TCP transparent data communication in a DVB satellite network using the PSTN for the return channel functionality considering two different traffic models. The obtained theoretical results for the worst case traffic model are verified by means of measurements on real DVB satellite network.The results also verifies the already known recommendations for an efficient operation of a TCP network which also includes the parameter setting.
INTERNET SERVICES ON DIGITAL
VIDEO BROADCASTING
NETWORKSWhile the early focus on Digital Video Broadcasting Networks was mainly on digital TV distribution, advances in the network standardization process ETSI 971 supporting the IP transparent data transfer and the availability of intelligent Set Top Boxes (STB) with retum channel capability offer new interactive services. An advanced software architecture of a STB offering also TCP/IP communication is presented in [LONC 001. Currently a significant growth in applications where asynchronous data transfer is involved in conjunction w i t h VideoIAudio distribution is appearing. Examples of such applications are intemeVWWW access or distributing corporate data. Focusing on the internetfWWW access two service classes can be offered. Either the Push Service based upon a Data Carousel Mechanism or the On demand (Pull) Service using a transparent TCP/IP communication between the WWW server and the STB. Figure 1 shows a typical configuration of a DVB Network offering digital-TV broadcast services, the push data service employing a Data Carousel Server and the pull service employing a WWW server. The TCP-data are delivered over-air. The RequesVACKdata is transferred using the PSTN.
Currently available Set-Top-Boxes (STBs) are mainly used for digital TV reception. The User Interface (UI) and the U1 dialog of such a device usually focus on its technological aspects and to a large degree ignore the needs of the user. The impact is that the user quite often is unsatisfied when interacting with the device. Recent U1 design approaches [9] [10] are proving that the focus should be put on the tasks that the user can perform with a STB rather than its underlying technical capabilities.However, modem design approaches both for the STB U1 as well as its underlying system architecture can be incorporated into a complete system design with reasonable effort. This paper presents the architecture of the "d-box", a STB being used for broadcasting TV services as well as future interactive services like internet, home-shopping etc. in Germany. The layered software architecture employs a Java Virtual Machine offering a high degree of independency of its underlying hardware. Emphasis is put upon the user-friendliness of the device by providing a uniform U1 both for experts and novices, therefore allowing intuitive and easy access for different user groups.
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