Hilmar Linder

Internet over direct broadcast satellites

High-powered direct broadcast television satellites can be used to broadcast high volumes of data directly to home terminals. Using the telephone network or a similar low-speed network, an asymmetrical system can be implemented which offers interactive Internet services. Two such interactive data broadcast systems are described which have been implemented as demonstration platforms for interactive multimedia services; one is based on digital subcarrier techniques for analog television channels, the other on the MPEG-2 and DVB standards. The architecture of the hardware and software is presented, particularly the solutions available for carrying Internet datagrams over MPEG-2 transport systems. A multicast transport protocol with selectable reliability is described which is the basis of a generic distribution application. It exploits the potential benefits of direct broadcast satellites for delivering data to large groups of local caches.

MPEG-2 as a transmission system for Internet traffic

MPEG-2 is an international standard defining compression algorithms for video and audio. Additionally, the standard defines a packet and cell oriented transmission system for the resulting digital streams. This system has been used as a local network to carry Internet traffic over a direct broadcast satellite. Applications have been developed for either unicast or multicast services from a base station server to a group of receiving clients. Inexpensive integrated receiver/decoder cards are used which contain a complete RF receiver, demodulator and decoder and interface directly to the PC bus. The paper describes the encapsulation and the implementation of a prototype system based on the European DVB standards which has been operational since early 1997. It then discusses some of the design decisions and suggests a generic encapsulation mechanism for future data and multimedia applications using MPEG-2 as a transport system.

A forward error correction based multicast transport protocol for multimedia applications in satellite environments

Multimedia services in satellite environments, for example electronic newspaper distribution, do not require the clients to have a full duplex link during the whole time of the broadcast. In order to control the transmission errors on the satellite channel, a generic concept for transport layer based forward error correction (FEC) is proposed and has been implemented in the restricted reliable multicast protocol (RRMP). For efficient support of multimedia services such as real-time voice, video and data distribution, RRMP offers frame oriented data transmission, rate control, multicast connection management facilities and mechanisms for different degrees of reliable data transmission by employing FEC based error control. The FEC concept developed for RRMP is based on Reed-Solomon burst erasure (RSE) codes combined with interleaving of corresponding parts of the transport service data units (TSDUs). The proposed concept allows the reconstruction of one completely lost transport protocol data unit (TPDU) within a TSDU. Performance experiments in a simulated satellite environment are discussed to demonstrate the error correction capabilities of the proposed FEC concept and to show the effect of the redundant control information on the throughput and packet loss in satellite environments.

Satellite Internet services using DVB/MPEG-2 and multicast Web caching

Communication satellites can be used to broadcast large volumes of data directly to extensive user groups. With the latest generation of high-powered direct broadcast satellites and the changing traffic and usage patterns in the Internet, new ways of using satellites for delivering data directly to the end user have become viable alternatives to terrestrial point-to-point networks. In this article the software architecture of a distributed system, which has been successfully implemented and which supports online and offline interactive multimedia services, is presented. It is based on a method of carrying Internet datagrams over DVB/MPEG-2 transport systems, intended for digital television. It relies on a configuration using a broadband forward channel and a separate, usually narrowband, return channel. The forward link is usually provided by a geostationary satellite, whereas the return channel uses a different network technology, such as dialup connection, a direct Ku-band return link, a LEO satellite network, or an LMDS local distribution system. A generic multicast system is presented which exploits the inherent capabilities of satellites to reach a large number of customers. The reliable multicast strategy chosen is shown to handle multiple applications, each with different reliability and timing requirements.

A lightweight encapsulation protocol for IP over MPEG-2 networks: design, implementation and analysis

Digital TV Broadcast standards (e.g., ATSC, DVB) offer a good solution to last mile Internet delivery. Satellites, terrestrial broadcast, and cable systems are well suited to the delivery of high bandwidth data to the end user. Low transport overhead and ready availability of MPEG-2 TS equipment make it very appealing as a bearer for connecting IP networks. The Multi-Protocol Encapsulation (MPE) is a standard for the transport of IP over DVB. However, MPE has a number of shortcomings and inefficiencies when supporting next generation Internetworking systems. This paper describes a new method for the encapsulation of IPv4/IPv6 datagrams, known as the Ultra Lightweight Encapsulation (ULE) that overcomes limitations of MPE. The paper provides the rationale for developing ULE and provides measurements and analysis to show that the new scheme can offer additional functionality while achieving increased transmission efficiency.

Scalable multicast data distribution for different transport service classes

Not all of the problems of large scale multicast can be addressed by automated repeat request (ARQ) based multicast protocols. Simulation studies have shown that independent packet loss among receivers is a worst case situation, where ARQ based protocols scale poorly and react with throughput degradation. Software based forward error correction (FEC) techniques are therefore a good solution and can be used to enhance the throughput efficiency by controlling the packet loss rate. A new method for implementing FEC at the transport layer is presented and performance measurements are shown. The difference between the restricted reliable multicast protocol (RRMP) and existing ARQ/FEC based multicast protocols is the flexibility and adaptability the RRMP provides by offering different transport service classes for different application needs. An application is able to choose the transport service, which best meets the requirements for efficiency, latency, delay, scalability etc. The design and implementation decisions for the FEC and ARQ based error recovery are outlined. Performance measurements demonstrate the suitability of FEC for real-time data transmissions.

Distribution of Remote Sensing Data via Satellite using DVB/MPEG-2 and Reliable Multicast

In this paper, a software system for distribution of remote sensing data to various European institutions is presented. The system uses DVB/MPEG-2 based transport links for carrying IP datagrams. It uses a broadcast satellite forward channel and a terrestrial return channel. The forward link is provided by a geostationary, digital TV satellite whereas the return channel uses leased telephone lines.