Ravenloft and 8b/10b encoding: Difference between pages

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In [[telecommunication]]s, '''8B/10B''' is a [[line code]] that maps [[8-bit]] symbols to [[10-bit]] symbols to achieve [[Direct current|DC]] balance and bounded disparity, and yet provide enough state changes to allow reasonable clock recovery. This means that there are just as many "1"s as "0"s in a string of two symbols, and that there are not too many "1"s or "0"s in a row. This is an important attribute in a signal that needs to be sent at high rates because it helps reduce "[[intersymbol interference]]". The code was described in 1983 by Al Widmer and Peter Franaszek in the [[IBM]] Journal of Research and Development. IBM was issued a patent for the scheme the following year.

'''Ravenloft''', a [[fiction]]al [[campaign setting]] for the ''[[Dungeons & Dragons]]'' [[role-playing game]], is a pocket dimension ("demiplane") consisting of a collection of "domains" brought together by mysterious powers known only as Dark Powers. The domains are separated from each other by the impenetrable Mists. Each ___domain is ruled by its dark lord, who has committed a crime so foul as to attract the attention of the Dark Powers and be imprisoned, seemingly forever (though some can be killed and replaced), in their ___domain, which they are not able to escape by any means magical or mundane. The Mists play with them by denying their most coveted dream, be it love, glory in war, or the defeat of their enemies.

As the scheme name suggests, 8 [[bit]]s of data are transmitted as a 10-bit entity called a ''Symbol'', or ''Character''. The low 5 bits of data are encoded into a 6-bit group and the top 3 bits are encoded into a 4-bit group. These code groups are concatenated together to form the 10-bit Symbol that is transmitted on the wire. The ''Data Symbols'' are often referred to as Dxx.y where xx ranges from 0-31 and y from 0-7. Standards using the 8B/10B encoding also define ''Special Symbols'' (or ''Control Characters'') that can be sent in place of a ''Data Symbol''. They are often used to indicate end-of-frame, link idle, skip and similar link-level conditions. They are referred to as Kxx.y and have different encodings from any of the Dxx.y symbols. Because 8B/10B encoding uses 10-bit symbols to encode 8-bit words, each of the 256 possible 8-bit words can be encoded in two different ways, one the bit-wise inverse of the other. Using these alternative encodings, the scheme is able to affect long-term DC-balance in the serial data stream, allowing links to be capacitively coupled.

Ravenloft is primarily a [[Goth]]ic [[horror fiction|horror]] setting. [[Dungeon Master]]s (DMs) are encouraged to use scenes that build apprehension and fear, culminating in the eventual face-to-face meeting with the nameless evil. Characters have a much greater significance attached to their acts, especially if they are morally impure, as they risk coming under the influence of the Dark Powers and gradually transforming themselves into a figure of evil, in the form of failed power checks.

The encoding is normally done entirely in hardware based on lookup tables. Upper levels of the software stack should be unaware that this encoding is being used.

Ravenloft is noted for its use of [[analogues]] of fictional characters from [[Gothic]] and [[horror fiction|horror]] [[literature]] and, rarely, historical figures. Examples include Count [[Strahd von Zarovich]] and [[Vlad Drakov]], who are [[analogues]] of [[Bram Stoker]]'s character Count [[Dracula]] and his historical inspiration, [[Vlad Tepes]], respectively; Doctor [[Victor Mordenheim]] and his creation, [[Adam (Ravenloft)|Adam]], analogues of [[Mary Shelley]]'s characters Doctor [[Frankenstein]] and his [[Creature]], and [[Frantisek Markov]], an analogue of [[H.G. Wells]]' character [[Doctor Moreau]].

Among the areas in which 8B/10B encoding finds application are [[Fibre Channel]], [[Gigabit Ethernet]], [[InfiniBand]], [[XAUI]], and audio storage devices such as the [[Digital Audio Tape]] and [[Digital Compact Cassette]] (DCC). The related [[Eight-to-Fourteen Modulation]] is used in the [[Compact Disc]] standard. The encoding scheme used in [[10 Gigabit Ethernet]]'s 10GBASE-R [[Physical Media Dependent]] (PMD) interfaces, 64B/66B, while similarly created with consideration of DC balance, maximum run length, transition density, electromagnetic emissions, and the like, is considerably different in design.

Ravenloft began life as a standalone adventure module for first edition Advanced Dungeons and Dragons. It was popular enough to spawn a pick-a-path book, a sequel module, and in the early 90's was launched as a full-fledged campaign setting. The campaign setting was revised three times before [[TSR]]/[[Wizards of the Coast]] cancelled the line.

==External links==

Currently Ravenloft is licensed to third-party publisher, [[White Wolf Game Studio]], who publish material compatible with the [[d20 System]].

*[http://domino.research.ibm.com/tchjr/journalindex.nsf/0/b4e28be4a69a153585256bfa0067f59a?OpenDocument Original paper by Franaszek and Widmer].

*[http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=/netahtml/search-bool.html&r=1&f=G&l=50&co1=AND&d=ptxt&s1=4486739.WKU.&OS=PN/4486739&RS=PN/4486739 US Patent 4,486,739], the relevant document at the US Patent and Trademark Office's site.

[[Category:Computer and telecommunication standards]]

See also: [[List of Ravenloft domains]]

[[Category:Line codes]]

[[fr:Encodage 8b/10b]]