Brian Frantz , Sterling Software

Research Center have been working with the United States satellite communication industry over the past 16 years to develop advanced communication and networking technologies to improve commercial satellite communications. With the recent explosion of the Internet and the enormous business opportunities available to communication system providers , great interest has developed in using commercial protocols over satellite networks. NASA Glenn has been addressing five major areas of concern regarding broadband satellite communications using commercial protocols: quality of service (QoS), interoperability, routing, traffic management , and protocol bandwidth efficiency. The first section of this article will briefly highlight various protocols used in the demonstrations and experiments and describe some of the important protocol characteristics relative to satellite communications. The second section will discuss completed and ongoing research that addresses three of the five major areas of concern: QoS, interoperability, and protocol efficiency. The experiments presented utilize asynchronous transfer mode (ATM), Transmission Control Protocol/Internet Protocol (TCP/IP), and Moving Picture Expert Group version 2 (MPEG-2) as the primary data delivery protocols. The following section briefly describes some important characteristics of these protocols. ATM is a protocol originally conceived by the telecommuni-cation industry to handle multimedia traffic over wide area networks (WANs). The protocol is a connection-oriented cell-switched protocol developed for fiber optic systems having near-error-free performance characteristics. The protocol encompasses features of both the data link and routing layers , layers 2 and 3 of the open systems interconnection (OSI) model. The main features of ATM are guaranteed QoS, ease of switching, and multimedia compliance. The ATM cell structure of 53 bytes was designed for high-bandwidth implementations with low switching and routing overhead. The ATM cell consists of a 5-byte header and 48-byte payload. The 5-byte header of each cell contains all the information necessary for the end-to-end delivery of the cell. If the header of the cell is corrupted beyond the cor-rective abilities of the included 1-byte cyclic redundancy check (CRC), the cell is discarded. The small header and limited routing rules allow the switching to be performed in high-speed hardware. The small size of the ATM cell — 53 bytes — allows small internal buffers to be used in the switches, keeping cell delay and jitter to a minimum. ATM requires that the order of ATM cells be maintained and the link be nearly error-free. These requirements directly affect the design of satellite and wireless networks that wish to utilize ATM. …