{"id":573,"date":"2020-04-07T19:33:39","date_gmt":"2020-04-07T17:33:39","guid":{"rendered":"http:\/\/tech.sosthe.sk\/?p=573"},"modified":"2020-11-10T08:24:33","modified_gmt":"2020-11-10T07:24:33","slug":"5-ethernet-csma-cd-kolizna-domena-duplex","status":"publish","type":"post","link":"http:\/\/tech.sosthe.sk\/index.php\/2020\/04\/07\/5-ethernet-csma-cd-kolizna-domena-duplex\/","title":{"rendered":"5. Ethernet – CSMA\/CD, kol\u00edzna dom\u00e9na, duplex"},"content":{"rendered":"

Ethernet<\/h3>\n

Ethernet<\/strong>\u00a0je rozsiahla rodina\u00a0sie\u0165ov\u00fdch technol\u00f3gi\u00ed<\/strong><\/em>\u00a0.\u00a0Ethernet predt\u00fdm vyu\u017e\u00edval na prenos d\u00e1t zdie\u013ean\u00e9 komunika\u010dn\u00e9 m\u00e9dium, ktor\u00fdm m\u00f4\u017ee by\u0165 metalick\u00fd \u010di optick\u00fd k\u00e1bel.\u00a0Ethernet je \u0161pecifikovan\u00fd normou\u00a0IEEE 802.3<\/strong>\u00a0.<\/p>\n

Ethernet<\/em><\/strong> je majoritn\u00e1 technol\u00f3gia pri budovan\u00ed lok\u00e1lnych siet\u00ed (LAN), ale m\u00e1 ve\u013ek\u00e9 zast\u00fapenie aj u v\u00e4\u010d\u0161\u00edch siet\u00ed. Sie\u0165ov\u00e1 technol\u00f3gia spad\u00e1 v ISO OSI modelu do\u00a0druhej (linkovej) vrstvy<\/em><\/strong>\u00a0, ale tie\u017e do prvej (fyzickej) vrstvy<\/em><\/strong>. Definuje rad parametrov, \u010do sa t\u00fdka kabel\u00e1\u017ee (prenosov\u00e9ho m\u00e9dia) a sign\u00e1lov, to je 1. vrstva. Ale tie\u017e popisuje sp\u00f4sob pr\u00edstupu k sieti a v\u0161eobecn\u00e9 adresovacie form\u00e1ty, to je 2. vrstva.<\/p>\n

Pr\u00edkladom \u010fal\u0161\u00edch sie\u0165ov\u00fdch technol\u00f3gi\u00ed, ktor\u00e9 boli v\u00e4\u010d\u0161inovo nahraden\u00e9\u00a0Ethernetom<\/em>\u00a0, je\u00a0FDDI<\/em>\u00a0,\u00a0Token Ring<\/em>\u00a0\u010di\u00a0ARCNET<\/em>. Druhou technol\u00f3giou, ktor\u00e1 m\u00e1 v\u00fdznamnej\u0161\u00ed podiel v LAN a ktorej pou\u017eitie rastie, je WiFi<\/em><\/strong>\u00a0– bezdr\u00f4tov\u00e1 sie\u0165, \u0161tandardizovan\u00e1 v\u00a0\u00a0IEEE 802.11<\/strong>\u00a0.<\/p>\n

P\u00f4vodne sa ako prenosov\u00e9 m\u00e9dium vyu\u017e\u00edval\u00a0tu\u010dn\u00fd koaxi\u00e1lny k\u00e1bel<\/em><\/strong> (10Base-5 \u010di slab\u00fd koaxi\u00e1lny k\u00e1bel 10Base-2) v zapojen\u00ed zdie\u013eanej zbernice. Prenosov\u00e1 r\u00fdchlos\u0165 bola 10Mb\/s. Postupne bol nahraden\u00fd\u00a0kr\u00fatenou dvojlinkou<\/em><\/strong> (twisted pair) zapojenou do hviezdy (vyu\u017e\u00edval sa hub). Pri r\u00fdchlosti 10Mb\/s sa ozna\u010doval iba ethernet<\/em> (10Base-T). Posledn\u00e9 m\u00e9dium pre Ethernet je\u00a0optick\u00e9 vl\u00e1kno<\/em><\/strong> (10Base-F). Postupom \u010dasu r\u00e1stli r\u00fdchlosti na 100Mb\/s ozna\u010dovan\u00e9 ako\u00a0Fast Ethernet<\/em><\/strong> (potrebn\u00e9 100Base-TX), 1Gb\/s ozna\u010dovan\u00e9 ako Gigabit Ethernet<\/em><\/strong>\u00a0(potrebn\u00e9 1000Base-T) a dnes m\u00e1me \u0161tandard aj pre\u00a0desa\u0165gigabitov\u00e9 Ethernet<\/em><\/strong>\u00a0(10GBase-T).\u00a0Rovnako tak boli\u00a0huby <\/em>nahraden\u00e9\u00a0switchmi<\/em><\/strong>\u00a0, teda spojmi bod-bod, a technol\u00f3gia sa ozna\u010duje\u00a0prep\u00ednan\u00fd Ethernet<\/em><\/strong>\u00a0(switched Ethernet), kde sa u\u017e nevyu\u017e\u00edva zdie\u013ean\u00e9 m\u00e9dium.<\/p>\n

Pre ur\u010dit\u00e9 typy Ethernetu je v\u017edy definovan\u00fd patri\u010dn\u00fd k\u00e1bel.\u00a0Pre optiku m\u00f4\u017eeme ma\u0165 jednovidov\u00e9 \u010di mnohovidov\u00e9 vl\u00e1kna dan\u00fdch parametrov.\u00a0Pre metaliku sa pou\u017e\u00edva tienen\u00e1 (STP –\u00a0Shielded Twisted Pair<\/em>\u00a0) \u010di netienen\u00e1 (UTP –\u00a0Unshielded Twisted Pair<\/em> ) kr\u00faten\u00e1 dvojlinka. Naviac je raden\u00e1 do nieko\u013ek\u00fdch kateg\u00f3ri\u00ed pod\u013ea vlastnost\u00ed a mo\u017enosti pou\u017eitia pre ur\u010dit\u00fd ethernet, m\u00e1me napr\u00edklad UTP k\u00e1bel kateg\u00f3rie 3, 4, 5, 5e, 6, 6a \u010di 7.<\/p>\n

Pr\u00edstup k m\u00e9diu – CSMA\/CD<\/h4>\n

Ke\u010f je viac zariaden\u00ed, pripojen\u00fdch k zdie\u013eanej zbernici, tak v jednej chv\u00edli m\u00f4\u017ee komunikova\u0165 iba jedno zariadenie a ostatn\u00e9 m\u00f4\u017eu len po\u010d\u00fava\u0165. Probl\u00e9m nastane, ke\u010f viac zariaden\u00ed za\u010dne komunikova\u0165 naraz. V tej chv\u00edli d\u00f4jde ku kol\u00edzii<\/strong>\u00a0.\u00a0Pre vysielanie (pr\u00edstup k m\u00e9diu) sa pou\u017e\u00edva\u00a0Carrier Sense Multiple Access With Collision Detection<\/em><\/strong> (CSMA\/CD) ako sie\u0165ov\u00fd kontroln\u00fd protokol.<\/p>\n

\"\"<\/p>\n

Algoritmus CSMA \/ CD<\/h4>\n
    \n
  1. zariadenie, ktor\u00e9 chce vysiela\u0165, po\u010d\u00fava, \u010di je linka vo\u013en\u00e1<\/li>\n
  2. ak je vo\u013en\u00e1, za\u010dne vysiela\u0165 r\u00e1mec<\/li>\n
  3. odosielate\u013e po\u010d\u00fava, \u010di nedo\u0161lo ku kol\u00edzii<\/li>\n
  4. ak zist\u00ed, \u017ee do\u0161lo ku kol\u00edzii, po\u0161le jam sign\u00e1l<\/li>\n
  5. po ukon\u010den\u00ed jamu si stanice, ktor\u00e9 vysielali nastav\u00ed n\u00e1hodn\u00fd \u010das po ktor\u00fd \u010dakaj\u00fa<\/li>\n
  6. po uplynut\u00ed \u010dasu sa za\u010dne bodom 1<\/li>\n<\/ol>\n

    Kol\u00edzna dom\u00e9na<\/h3>\n

    Kol\u00edzna dom\u00e9na<\/strong>\u00a0(collision domain) je \u010das\u0165 siete, kde m\u00f4\u017ee d\u00f4js\u0165 ku kol\u00edzii vysielania nieko\u013ek\u00fdch stan\u00edc.\u00a0Teda skupina zariaden\u00ed, ktor\u00e9 s\u00fa pripojen\u00e9 na zdie\u013ean\u00e9 m\u00e9dium.\u00a0To je v praxi pr\u00edklad star\u00fdch sie\u0165ov\u00fdch rozvodov pomocou koaxi\u00e1lneho k\u00e1bla.\u00a0Alebo pou\u017e\u00edvanie\u00a0hubov<\/em><\/strong> (rozbo\u010dova\u010d), ktor\u00e9 prijat\u00fd packet preposielaj\u00fa na v\u0161etky rozhrania naraz mimo toho odkia\u013e pri\u0161iel.<\/p>\n

    \"\"<\/p>\n

    Predt\u00fdm sa pre rozdelenie siete na viacer\u00fdch kol\u00edznych dom\u00e9n (a ich zmen\u0161enie) vykonalo to, \u017ee sa sie\u0165 rozdelila na viac segmentov a tie sa prepojili pomocou routera.\u00a0Potom sa ale objavili\u00a0switche<\/em><\/strong> (prep\u00edna\u010d), ktor\u00e9 z princ\u00edpu svojej funkcie, vytv\u00e1raj\u00fa samostatn\u00e9 kol\u00edzne dom\u00e9ny na ka\u017edom rozhran\u00ed. Switch toti\u017e posiela prijat\u00fd packet iba na jedno rozhranie (v nau\u010denom stave) a vykon\u00e1va prep\u00ednanie paketov.<\/p>\n

    \"\"<\/p>\n

    Ak je do switcha pripojen\u00e9 koncov\u00e9 zariadenie alebo in\u00fd switch a linka je plne duplexn\u00e1, tak na tejto linke nem\u00f4\u017ee d\u00f4js\u0165 ku kol\u00edzii. Prakticky to toti\u017e znamen\u00e1, \u017ee m\u00e1me dve komunikuj\u00face zariadenia na linke, a ka\u017ed\u00e9 zariadenie posiela d\u00e1ta po vlastnom p\u00e1re vodi\u010dov.<\/p>\n

    Duplex<\/h3>\n

    Half duplex<\/strong>\u00a0– polovi\u010dn\u00fd duplex znamen\u00e1, \u017ee akt\u00edvna m\u00f4\u017ee by\u0165 komunik\u00e1cia iba v jednom smere.<\/p>\n

    Full duplex<\/strong> – pln\u00fd duplex je vo chv\u00edli, kedy m\u00f4\u017eeme z\u00e1rove\u0148 vysiela\u0165 aj prij\u00edma\u0165. V ethernete sa vyu\u017e\u00edvaj\u00fa dva p\u00e1ry vodi\u010dov (v\u00e4\u010d\u0161inou, ale \u0161tyri), kedy polovica je pou\u017eit\u00e1 iba pre vysielanie a polovica pre pr\u00edjem. Odpadaj\u00fa tu probl\u00e9my a oneskorenia sp\u00f4soben\u00e9 algoritmom CSMA\/CD a teoretick\u00e1 r\u00fdchlos\u0165 je dvojn\u00e1sobn\u00e1 (u fast ethernetu je 100Mb\/s pou\u017eit\u00e9 pre vysielanie a 100Mb\/s pre pr\u00edjem).<\/p>\n

    Pozn .:<\/strong><\/em> Huby nepodporuj\u00fa plne duplexn\u00fa komunik\u00e1ciu, preto\u017ee tu m\u00f4\u017ee d\u00f4js\u0165 ku kol\u00edzii. Ak dve stanice vysielaj\u00fa naraz, hub to prijme a odo\u0161le na ostatn\u00e9 porty, tak\u017ee vlastne odosiela v kol\u00edzii.<\/p>\n","protected":false},"excerpt":{"rendered":"

    Ethernet Ethernet\u00a0je rozsiahla rodina\u00a0sie\u0165ov\u00fdch technol\u00f3gi\u00ed\u00a0.\u00a0Ethernet predt\u00fdm vyu\u017e\u00edval na prenos d\u00e1t zdie\u013ean\u00e9 komunika\u010dn\u00e9 m\u00e9dium, ktor\u00fdm m\u00f4\u017ee by\u0165 metalick\u00fd \u010di optick\u00fd k\u00e1bel.\u00a0Ethernet je \u0161pecifikovan\u00fd normou\u00a0IEEE 802.3\u00a0. Ethernet…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12],"tags":[],"_links":{"self":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/573"}],"collection":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/comments?post=573"}],"version-history":[{"count":5,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/573\/revisions"}],"predecessor-version":[{"id":814,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/posts\/573\/revisions\/814"}],"wp:attachment":[{"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/media?parent=573"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/categories?post=573"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/tech.sosthe.sk\/index.php\/wp-json\/wp\/v2\/tags?post=573"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}