Milestone Technologies Inc. PO Box 37145 Raleigh, NC 27627 Phone: (919) 856-0700 Fax: (919) 856-8600 info@milestonetechnologies.com SATX(TM) DATA BROADCASTING FILE TRANSFER PROGRAM Introduction This article describes a sophisticated communications software product, called SATXTM. SATXTM is designed to operate on IBM and compatible PCs and is designed to transfer binary files over one- way or broadcast only data networks error free. SATXTM was originally developed for use in Direct Broadcast Satellites (DBS) systems, but can potentially be used over any one way (simplex) data link. FM radio subcarriers and TV using VBI (Vertical Blanking Interval) are also excellent potential applications for SATXTM.. Even DTV and HDTV stations can use SATXTM to broadcast data files. The development of SATXTM is significant because it is an "off the shelf" software solution for transferring binary files reliably in data broadcasting applications. SATXTM can be combined with many "off the shelf" hardware components today to create an excellent data broadcasting network. Not only does SATXTM make it easier for companies to begin utilizing DBS services, but it is now much easier for FM radio and TV stations to implement data broadcasting applications. Background In recent years, DBS services (often referred to as one-way or broadcast only services) have increased in popularity. This technology is an excellent method to get data to literally an unlimited number of remote sites economically and reliably. Of course the limitation is that these systems are not two way and do not allow the remote sites to send back data over the satellite link. Nonetheless, certain applications such as trading networks, financial news networks, wire services, large "chain" businesses, and other industries are well suited for this technology. Most companies have had to develop their own software to utilize DBS services. Software to transfer text streams, or other running streams of data is relatively straightforward. Transferring files error free, especially large files such as multi-media files or graphics files, is much more complex, and has been a significant stumbling block for some applications developers and information providers. Before SATX, there was not a commercially available, standalone, software program for IBM and compatible PCs designed to transfer binary files error free over a simplex link. Under development since 1990, SATXTM (short for SATellite Xfer) has become the ideal software tool for data distribution. Using SATXTM, direct broadcast satellites can be utilized to send multi- media, graphics, compressed files, database files, and virtually any other file type. It is even possible to transfer entire software applications over one way satellite links. The technology works equally well for two-way VSAT systems when placed in a broadcast mode. SATXTM was designed from the ground up for the purpose of transferring files over a one way data link. It is not a modified version of a two way (duplex) protocol. SATXTM is highly customizable to a particular application because of the flexibility of its proprietary ThunderfileTM protocol. This new protocol can even be varied by the network operator to accommodate harsh broadcasting conditions, such as that created by severe weather. Other Potential Applications SATXTM has the potential to be used in a variety of applications and industries. SATXTM can potentially be incorporated into radio and TV applications which broadcast data over subcarriers. It is also possible to utilize SATXTM in DTV and HDTV applications that are emerging today. The Problem That Only SATXTM Can Solve Data has been transferred for years over satellite links and broadcast networks, so why is there a need for a product like SATXTM? To answer this requires a brief review of the techniques commonly used to send data over simplex links today, and the type of data commonly transferred. Basic Methods For Simplex Data Transfer The methods for transferring data over simplex links fall into two basic categories, FEC (Forward Error Correction), and automatic repetition of the desired data. FEC codes are great for improving the overall reliability of a data link and have been used in satellites for years. The latter technique is effective because is it is often easier and less expensive to simply repeat the desired data, and hope that the second or subsequent tries are successful if the first one suffers an error. Repeating the data is often necessary because FEC cannot correct data subjected long error bursts or missing data packets. Simplex data techniques today usually employ one or both of these concepts. These techniques are adequate for transferring small blocks of data or for data streams. Digital audio and even digital video applications can tolerate a certain error rate without creating noticeable problems for the end user. Some applications transfer a stream of packetized data and the receiving PC simply throws away packets with errors. Since binary files, such as database files and software programs, must be transferred error free, a more sophisticated approach is needed. Many systems do not have the capability to transfer binary files directly, thus creating the need for SATXTM. Why FEC Alone Is Not Enough - The File Transfer Problem To transfer a file, the data transfer method must do more than improve the overall reliability of a data link. Binary files must be transferred error free to be useful to the receiving PC, or disaster is likely. It would be nice if we could always employ a data link that was guaranteed not to suffer any errors for the duration of a file transfer. Unfortunately, this is not a realistic assumption for most one way systems. This is especially true for large files, because the larger the file, the longer the data transfer would have to operate without experiencing any errors in the data link. While it might be possible to transfer a 50 kbyte file at 9600 bits/sec without difficulty, it is not realistic to expect to transfer a 12 MB file without having to deal with some errors in the data stream! FEC codes can correct for minor errors in the data stream. Unfortunately, many errors are not minor. Even in satellites, where typical raw links are quoted as experiencing only one error in ten million bits, a single error burst can corrupt a long series of characters. In a file transfer system that relies solely on FEC, if the FEC algorithm cannot correct for the errors that occur during a file transfer, some systems will throw away the entire file at the receiving site. To transfer a large file successfully over a simplex link requires the data transfer method to be able to recover from these error bursts and multiple errors per file transferred, and still be able to receive an error free file. This is exactly what SATXTM is designed to accomplish! More Than A File Transfer Program SATXTM does more than just transfer files. SATXTM provides a complete record of all transactions and monitors performance. Monitoring logs on SATXTM Transmit and SATXTM Receive keep a detailed record of all files sent and received. SATXTM Receive also maintains a log of all real time errors encountered. The error log can record more than 30 different error codes which help to determine the type of error and the frequency of errors. It is often possible to distinguish between errors which occur during transmission and those caused by hardware problems. Data Integrity and Reliability Second To None SATXTM has two layers of error detection. The first is the well known and respected use of CRC32s, which is reliable enough for modern day LANs! The second method takes advantage of retransmitted data. SATXTM can use duplicate data which is retransmitted to verify data integrity at the bit level, if desired. SATXTM provides even more thorough error detection and data verification methods than what is available on typical two way protocols! It's all designed to provide confidence to the user of SATXTM Receive that if the data is there, it's reliable! Customization Available If SATXTM has potential in your business applications, but you need additional features or capability, let us know. Customized versions can be made available. Call or write to let us know your needs and we can provide you with a free estimate. SATXTM and ThunderfileTM are trademarks of Milestone Technologies Inc. SATXTM , Copyright 1992 -1999 Milestone Technologies Inc., All Rights Reserved. Milestone Technologies Inc. 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