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IEEE 802.11

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Hidden : 05/05/2006
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IEEE 802.11

IEEE 802.11 neboli Wi-Fi. Wi-Fi je zkratka pro termin Wireless Fidelity, kterym se oznacuje jeden z technologickych standardu bezdratove komunikace (prakticky jsou jako Wi-Fi kompatibilni oznacena bezdratova zarizeni ruznych vyrobcu, ktere spolu navzajem bez problemu spolupracuji). Technologie Wi-Fi vyuziva bezlicencni frekvencni pasmo 2,4GHz. Technicky jde o standard IEEE (Institute of Electrical and Electronics Engineers) 802.11b pro vysokorychlostni bezdratove prenosy, datove kompatibilni s metalickou (dratovou) siti ethernet. Wi-Fi umoznuje uzivatelum snadne pripojeni k siti v maximalni prenosove rychlosti 125Mbit/s (Afterburner technology) na vzdalenost nekolika stovek metru ci kilometru. (Vzdalenost, na kterou se lze pripojit vzdy zalezi na typu pouzite anteny a konkretnich mistnich podminkach).
Aktualizovano: Nejnovejsi Wi-Fi zarizeni umeji komunikovat rychlosti az 270Mbit/s. Toto je umozneno novou technologii MIMO (Multiple In/Multiple Out), ktera umoznuje vysilat i prijimat nekolik datovych toku najednou v ramci jednoho kanalu.

Zajimavost:

Vzdalenost 200 kilometru preklenuli prostrednictvim Wi-Fi vysokoskolaci z Cincinnati. Komunikace probihala plnou rychlosti standardu 802.11b – 11Mbit/s, bez zesileni signalu. Pro vytvoreni tohoto noveho svetoveho rekordu pouzili vlastnorucne upravenou satelitni antenu o prumeru 3,66 metru.

Historie IEEE 802.11

V roce 1991 si firmy vyrabejici tato bezdratova zarizeni uvedomily, ze pokud chteji dosahnout co nejvetsiho rozsireni bezdratovych LAN siti a jejich vseobecneho prijeti, musi byt standardizovany. Zacaly proto smerovat sve konani vzhledem k tomuto dulezitemu kroku.
Nekdy v roce 1992 zacali vyrobci bezdratovych zarizeni vyvijet produkty pracujici v bezlicencnim pasmu 2.4GHz. S timto krokem prislo rozsireni bezdratovych siti do dalsich dvou, velmi lukrativnich trhu. Prvnim bylo zdravotnictvi, ktere zacalo pouzivat mobilni prenosna zrizeni pro pristup k lekarskym zaznamum pacientu. Pocitace si take nasly cestu do skol a trid, skoly a vyukova zarizeni zacala instalovat bezdratove site aby se vyhnula pokladani kabelu klasickych lokalnich siti.
V roce 1997 vydala standardizacni organizace IEEE (Institute of Electrical and Electronic Engineers) standard 802.11 upravujici pravidla a technicke parametry pro lokalni bezdratove site. Standard obsahuje definici pro prenos v infracervenem pasmu a dve metody prenosu v pasmu 2.4GHz. Maximalni rychlost prenosu dle tohoto standardu cini 2 Mbit/s.
V roce 1998 byl schvalen standard 802.11c, ktery pouze resi praci komunikacnich mostu (bridges) v ramci podvrstvy MAC. Je pouzivan vyrobci mostu a pristupovych bodu.
V roce 1999 byl schvalen novy standard 802.11b, poskytujici prenosovou kapacitu az 11Mbit/s na fyzicke vrstve v pasmu 2.4GHz, pouziva technologii CCK (Complementary Code Keying).
V roce 1999 byl dale schvalen standard 802.11a, poskytujici prenosovou kapacitu az 54Mbit/s na fyzicke vrstve, pracuje vsak v licencovanem pasmu 5GHz. Prace na tomto standardu zapocaly jeste pred zapocetim praci na 802.11b (jak pismenko napovida), ale implementace si diky vyssi slozitosti vyzadala vice casu. Pouziva OFDM modulaci (Orthogonal Frequency Division Multiplexing).
V roce 2001 byla schvalena norma 802.11d, ktera upravuje 802.11b pro jine kmitocty, nez je pasmo 2.4GHz. (Hlavne pro pasmo 5GHz)
V roce 2003 byla schvalena norma 802.11g, ktera nabizi prenosovou rychlost az 54Mbit/s v bezlicencnim pasmu 2.4GHz. Je zpetne kompatibilni s normou 802.11b (pomoci CCK a RTS/CTS). Pouziti technologii CCK a OFDM je povinne.

Velmi pekny clanek o Wi-Fi: (visit link)

CACHE:

Specialni vybaveni:
1) Zarizeni podporujici standard IEEE 802.11b nebo IEEE 802.11g

Na souradnicich N 50° 02.772 E 014° 26.004 najdete cislo ve tvaru ABCDEF. Nyni budete potrebovat zarizeni podporujici standard IEEE 802.11b Zapnete jej a dejte vyhledat vsechny dosptupne site. Najdete Wi-Fi sit, ktera ma v nazvu cislo ve trvaru KLMNO. Nyni vse dosadte a mate finalni souradnice:

N 50° BD.(K+N)E(F-M)
E 014° O(A+C).K(L-N)(M+N)

Cache je na fregventovanem miste, je zde spousta mudlu, budte opatrni. Nejlepsi je odlov nekdy rano, nebo taky pozde vecer.

POZOR! Pro uznani nalezu je nutne, aby jste v logu na gc.com uvedli, jake zarizeni jste pouzili pro odloveni teto cache. (znacka, model, typ) napr.: PCMCIA ASUS WL-100G Deluxe

IEEE 802.11

IEEE 802.11, the Wi-Fi standard, denotes a set of Wireless LAN/WLAN standards developed by working group 11 of the IEEE LAN/MAN Standards Committee (IEEE 802). The term 802.11x is also used to denote this set of standards and is not to be mistaken for any one of its elements. There is no single 802.11x standard. The term IEEE 802.11 is also used to refer to the original 802.11, which is now sometimes called "802.11legacy." For the application of these standards see Wi-Fi.
The 802.11 family currently includes six over-the-air modulation techniques that all use the same protocol. The most popular (and prolific) techniques are those defined by the b, a, and g amendments to the original standard; security was originally included and was later enhanced via the 802.11i amendment. Other standards in the family (c–f, h–j, n) are service enhancements and extensions or corrections to previous specifications. 802.11b was the first widely accepted wireless networking standard, followed (somewhat counterintuitively) by 802.11a and 802.11g.
802.11b and 802.11g standards use the 2.4 gigahertz (GHz) band, operating (in the USA) under Part 15 of the FCC Rules and Regulations. Because of this choice of frequency band, 802.11b and 802.11g equipment can incur interference from microwave ovens, cordless telephones, Bluetooth devices, and other appliances using this same band. The 802.11a standard uses the 5 GHz band, and is therefore not affected by products operating on the 2.4 GHz band.
Which part of the radio frequency spectrum may be used varies between countries, with the strictest limitations in the USA. While it is true that in the USA 802.11a and g devices may be legally operated without a license, it is not true that 802.11a and g operate in an unlicensed portion of the radio frequency spectrum. Unlicensed (legal) operation of 802.11 a & g is covered under Part 15 of the FCC Rules and Regulations. Frequencies used by channels one (1) through six (6) (802.11b) fall within the range of the 2.4 gigahertz Amateur Radio band. Licensed amateur radio operators may operate 802.11b devices under Part 97 of the FCC Rules and Regulations that apply.

CACHE:

Special equipment:
1) Device with IEEE 802.11b or IEEE 802.11g standards

At the coordinates N 50° 02.772 E 014° 26.004 you find number ABCDEF. Now you need device with IEEE 802.11b standard. Switch on device and find available wireless networks. One network has a number KLMNO in name. Now add all the numbers to a final coordinates:

N 50° BD.(K+N)E(F-M)
E 014° O(A+C).K(L-N)(M+N)

NOTICE! For approval „Find it“ you must write in log, what IEEE 802.11 device you use. (producer, type) For example: PCMCIA ASUS WL-100G Deluxe

Additional Hints (Decrypt)

[cz] zntargvpxn - cbq ynivpxbh
[en] zntargvp - haqre gur orapu

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)



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