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DO~Ffiloading and ADDRESSING VIA TELETEXT Gary W. Stanton

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DO~Ffiloading and ADDRESSING VIA TELETEXT Gary W. Stanton DO~ffiLOADING AND ADDRESSING VIA TELETEXT Gary w. Stanton Southern Satellite Systems ABSTRACT A teletext signal has been continuously typewriters, or not a large enough transmitted on the vertical interval supply of "t's" at their printer? These of Satcom I, transponder 6 since the questions aside, let's deal with what's NCTA show in 1980. The original purpose really happening. was the video dissemination of cable news services. Recently, the system There are some cable systems in the has been modified to incorporate data u.s. delivering "videotext," which for transmission which emulates a standard the purposes of this paper will be telephone line, but with far higher considered two-way and interactive. data reliability. In addition, the There are some broadcast stations test modified teletext system for data marketing their "teletext" services, transmission incorporates an which in this article will mean strictly addressability function with over five one-way. UPI, Reuters, Dow Jones, and million addresses possible. A priority Quotrader are all delivering their scheme for national, regional, local services, which are "teletext", to and individual addressing is described. cable systems, today and in the case A description of the system, including of Quotrader, to private users. UP! data from reliability tests is presented. and Reuters began satellite testing This will also define several key of the service in July 1980, and service technical requirements for successful to cable TV headends in October 1980. teletext data reception. But one-way teletext services aren't really what all the excitement is about. It's the interactive services that are General Information getting all the attention, and precipitating the hue and cry of the The cable and communications trades future of communications. The have been full of news about the up Warner-Qube system in Columbus, and and coming information invasion of the other such ventures like The Source home. With the British, the French in Virginia, are the kinds of things and the Canadians, among others, the that the cable and communications battle lines have been drawn about whose industry have been talking about so system is the best for delivering various much. videotext or teletext services into America's wired cable homes. Unfortunately, few of the things being Unfortunately, there's so much talk talked about are ready to happen on and so little really happening that a national basis today. That's why, it may be time to sit back and take if teletext isn't going to remain a a look at where this revolution really thing of the future, the industry needs is, what's really happening and what's to use what's available today to its just in the testing, a few years down full capacity. That means using the the road. existing means of teletext, one-way delivery, and make it two-way, in effect, One problem in all the talk is the fact by using telephone lines as the means that the generic jargon of the of "upstreaming." alphanumeric information industry is confusing. Are videotext and teletext Videotext is basically two-way the same thing? What about viewdata? communications, using a telephone line And why do some people leave the "t" to "call up" specific information, which off of videotex(t)? Do they have lazy is then delivered to the person who 161 requested it, using the same phone line. hours per day. It's "narrow stream," two-way delivery, which is interactive. The key to this application of existing, in-use today technology, is in what's called an "RS-232 decoder." RS-232 Teletext, on the other hand, is a one-way is an EIA defined standard computer "stream" of information (channels or serial data interface used for pages), delivered as a "wide stream." interconnection of many different Phone lines, the standard means of most devices. A printer or home computer operating text delivery today, do not can be attached to a RS-232 decoder, permit wide streams of information, as well as a cable system's character whereas broadcast or cable delivered generator as it's being used by UP!, teletext does. Two-way videotext is Reuters, Dow Jones, and View Weather selective and slow. One-way teletext today. The delivery of teletext is non-selective and fast. It takes information into businesses and homes a lot of transmission space to provide of "specialty" users is one of the two streams of information for the general markets soon to be tapped by the common public. Because of the various carrier Southern Satellite Systems, limitations inherent in both videotext through its teletext system called and teletext, there is need for both CableText. wide stream teletext, as well as interactive videotext. Let's look at the "downloading" application of teletext. An example The major drawbacks to interactive is being accomplished today by Quotrader, videotext services are the long distance a commodities service which utilizes phone charges, the cost of the receive a specially equipped computer along equipment, and the fee for the with the RS-232 decoder. The decoder information service itself. The interfaces with the microcomputer, downloading scenario outlined previously feeding the information into the computer enables users to accomplish most of for use in analyzing the commodities the same things they could accomplish information. The software provided using a two-way system, for less cost. as part of Quotrader's monthly fee also Downloading with satellite delivered enables users to receive buying and teletext information, as done by selling recommendations. Buy/sell orders CableText, and upstreaming via phone are placed by a phone call to a user's lines means teletext for specialty users broker, or by attaching the computer is not a thing of the future. It's being to a modem which permits the user's done today and can be done by any kind computer to talk directly to the broker's of information supplier who wishes to computer. do so. rhat scenario, starting with 1) In this application, subscribers will downloading information into a home be continuously "on-line," with their computer, or in some cases a printer, printer or computer storage device 2) storage of the information on the receiving the information transmitted computer storage device or on a printed for them. page, 3) viewing of the information at the convenience of the user, and While a satellite delivered teletext finally 4) the use of the information system can be delivering hundreds of for a phone transaction (upstreaming), different specialized types of is one application that is ready for information, individual subscribers the marketplace today. will receive only the information they want and need, because the teletext Existing System Formats decoders will be "addressable." A Teletext decoder will feed the data There are a number of teletext and into a user's printer or computer with videotext systems either proposed or storage. Though the information may in existence in either test or be delivered at 3 a.m., the user can operational modes. Some are very still "call it up" when he or she is similiar, differing only in minor ready to use it, either by instructing detail, however, just different enough the computer to display it, or by simply as to be incompatible. Others are reading the printed copy. If a significantly different in one or more subscriber needs to use the information respects. for a transaction, a simple telephone call will make a technically one-way system two-way in effect. DownloadLng the information via teletext makes the For background purposes, a brief system interactive only when needed, description of the various systems with information being delivered 24 is in order. 162 1. The first teletext systems does not specify transmission format, and by far the most widely used is the only presentation level, i.e. viewable United Kingdom (U.K.) system and its level format. This means the CRT and variations. The teletext version is printer presentation codes have been called Ceefax in Great Britain and the defined by the PLP format, but not the videotext version is called Prestal. transmission scheme. This system is also used in Australia and several other European countries. Since AT & T conceived the PLP format, Several variations of it are in use Teledon and CBS have arnrnended their in the United States, such as Field display system protocol to be compatible. Communications' "Keyfax" system and At this point there are basically two Southern Satellites' "CableText" system. major competitive incompatible systems KSL in Salt Lake City and WGN in Chicago in existence, the U.K. system, which also experimented with variations of includes both teletext and videotext the U.K. system. Reportedly, 1.5 million definitions, and the PLP presentation LSI chip sets have been sold for the system with the CBS videotext U.K. system. transmission definitions. The U.K. system features a mapped video Advantages/Disadvantages screen system where each screen alphanumeric character or mosaic graphic Much has been written on the comparative character's screen position is defined advantages of each system. However, by its position in the transmit stream. the engineering community must stand After the necessary page address or back and realize that the end user, header information is transmitted, whether a horne owner, business, or cable subsequent consecutive transmissions system really does not care what contain screen row numbers and the technical system is in use. All the information to be displayed on that end user is really interested in is: row. For example, the lOth character l) Obtaining the desired data transmitted with a row 4 address will or information be displayed in the lOth screen position 2) Reliability in row 4.
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