NAPLPS
From Wikipedia, the free encyclopedia
NAPLPS (North American Presentation Level Protocol Syntax) is a graphics language for use originally with videotex and teletext services. The basics of NAPLPS were later used as the basis for several other microcomputer based graphics systems.
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[edit] Description of operation
In Videotex applications the text and graphic data were encoded in 7- or 8-bit character format that could be transmitted via conventional data pathways such as X-25 or via ASCII modem. Typically, in Canada, a Bell 202 was used providing 1200 baud out and 75 baud return data rates.
In Teletext mode (using the NABTS protocol), Character codes were sent to users' televisions by encoding them as dot patterns in the vertical blanking interval of the video signal. A set top box attached to the TV decoded these signals back into text and graphic pages, which the user could select among. The data rate was quite slow (about 600 bit/s), resulting in largely static pages.
[edit] History
In the early 1980s a number of firms were providing videotex services, although the most popular by far were Minitel in France, Prestel in the UK and the now defunct Prodigy Service.
At about this time the Canadian government decided to create its own "second generation" service that would support both text and graphics, called Telidon.
In Teletext mode, it used considerably more of the vertical blanking interval, increasing the signalling rate to about 2400 bit/s. An additional "backchannel" was used to send data back to the hosting computers, typically over phone lines.
While the Prestel and Minitel systems were based on raster graphics with a relatively inexpensive receiver, Telidon was based on a simple graphics language that delivered a vector based graphic. This required a much more complex circuit to decode not only characters, but the graphics as well. Display results were vastly superior to the competitive technologies, but the cost of the decoding hardware was substantially higher. Typical Telidon decoders of the period employed Z80 or 6809 processors with RGB and or baseband output.
Graphics were encoded as a series of instructions (graphics primitives) each represented by a single ASCII character. Graphic coordinates were encoded in multiple 6 bit strings of XY coordinate data, flagged to place them in the printable ASCII range so that they could be transmitted with conventional text transmission techniques. These were referred to as Picture Description Instructions (PDIs). ASCII SI/SO characters were used to differentiate the text from graphic portions of a transmitted "page".
AT&T was so impressed by Telidon that they decided to join the project. They added a number of useful extensions, notably the ability to define your own graphics commands (macro) and character sets (DRCS). They also tabled algorithms for proportionally spaced text, which greatly improved the quality of the displayed pages.
A joint CSA/ANSI working group (X3L2.1) revised the specifications, which were submitted to the ANSI board for standardization and became ANSI T500, NAPLPS. Unfortunately some of the simplicity, elegance, and power of NAPLPS was lost because of a focus on implementation issues for the perceived large home information market - a market that exists today as "the Internet".
Business models for Telidon services were poorly developed. Unlike the UK, where teletext was supported by one of only two large companies whose whole revenue model was based on a read-only medium (television), in North America Telidon was being offered by companies who worked on a subscriber basis.
[edit] One-way systems
Telidon-based teletext was tested in a few North American trials in the early 1980s — CBC IRIS, TVOntario, MTS-sponsored Project IDA, to name a few.
NAPLPS was also part of the NABTS teletext standard, for the encoding & display of teletext pages.
In the late 1980s and early 1990s, SportsChannel ran a service called Sports Plus Network, which ran sports news and scores while SportsChannel was not otherwise on the air. The screens, which frequently featured team logos or likenesses of players in addition to text, were drawn entirely with NAPLPS graphics and resembled the loading of Prodigy pages over a modem, though slightly faster.
[edit] Two-way systems
Various two-way systems using NAPLPS appeared in North America in the early 1980s. The biggest North American examples were Knight Ridder's Viewtron (based in Miami) and the Los Angeles Times' Gateway service (based south of Los Angeles in Orange County). Both used the Sceptre NAPLPS terminal from AT&T. The Sceptre contained a slow modem that connected over the consumer's telephone line to host computers. The Sceptre was expensive whether purchased or rented. Despite huge investments by their parent companies, neither Viewtron nor Gateway lasted into the second half of the decade.
Other early-1980s NAPLPS technology was deployed in Canada, both as a way for rural Canadians to get news and weather information and as the platform for touchscreen information kiosks. In Vancouver these were featured at Expo 86. The kiosks became ubiquitous in Toronto under the name Teleguide, and were deployed in many shopping centres and at major tourist attractions. The latter city was the North American nexus of NAPLPS and the home of Norpak, the most successful of NAPLPS-oriented developers. Norpak created and sold hardware and software for NAPLPS development and display. TVOntario also developed NAPLPS content creation software.
London, Ontario - based Cableshare used NAPLPS as the basis of touch-screen information kiosks for shopping malls, the flagship of which was deployed at Toronto's Eaton Centre. The system relied on an 8085-based microcomputer which drove several NAPLPS terminals fitted with touch screens, all communicating via Datapac to a back end database. The system offered news, weather and sports information along with shopping mall guides and coupons. Cableshare also developed and sold a leading NAPLPS page creation utility called the "Picture Painter."
In the late 1980s, Tribune Media Services (TMS) and the Associated Press operated a cable television channel called AP News Plus that provided NAPLPS-based news screens to cable television subscribers in many U.S. cities. The news pages were created and edited by TMS staffers working on an Atex editing system in Orlando, Florida, and sent by satellite to NAPLPS decoder devices located at the local cable television companies. Among the firms providing technology to TMS and the Associated Press for the AP News Plus channel was Minneapolis-based Electronic Publishers Inc. (1985-1988).
In 1981, two amateur radio operators (VE3FTT and VE3GQW) received special permission from the Canadian Department of Communications to carry out on-air experiments using NAPLPS syntax which was technically not legal at the time because it was a "coded transmission". Following their report on the success of the tests, the DOC then permitted general use of NAPLPS on amateur radioteletype. This was reported in the ARRL Radio Handbook for several years following.
[edit] Decline
NAPLPS lived on into the early 1990s as the graphical basis for the Prodigy online service. Some bulletin boards were able to serve NAPLPS content to callers on their 1200 and 2400 bit/s modems. But the technology's chief advantage in an era of slow telecommunication -- its ability to encode complex graphics in terse object commands -- became moot as data communication speeds increased and raster graphics compression became popular.
[edit] Legacy
In the 1980s NAPLPS' basic geometry and command structure became the basis for the library-based GKS microcomputer standard, which was implemented in Digital Research's GSX graphics system and used in their GEM GUI. GKS was later extended into a 3D version, and additions to this resulted in PHIGS (Programmer's Hierarchical Interactive Graphics System), a competitor to OpenGL.
[edit] See also
Remote imaging protocol (a.k.a. RIPscrip)
