PCH 12 Ethernet Standards(以太網標準) <<
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PCH 12 Ethernet Technology(以太網技術)
learning objectives/學習目標
Recognize the typical network standards.
識別典型的網絡標準。
Before Ethernet was the dominant technology, there were multiple types of networking technologies competing for market share. At one point, Ethernet was just one of many competing standards, including token ring, fiber distributed data interface (FDDI), and more. By the late 1990s, a single standard was clearly the dominant choice in both office and residential networks: IEEE 802.3 Ethernet. Ethernet uses various media types, from coaxial cable to twisted-pair copper and fiber-optic cables (discussed in an earlier module). The 802.3 Ethernet standard and the concept of using frames for communication over various media, including Wireless 802.11, is predominant today, and it is vital to understand the fundamentals of Ethernet including the various speed and distance limitations each standard places on our networks.
在以太網成為主導技術之前，存在多種類型的網絡技術爭奪市場份額。一方面，以太網只是眾多競爭標準之一，包括令牌環，光纖分佈式數據接口（FDDI）等。到1990年代後期，單一標準顯然已成為辦公室和住宅網絡中的主要選擇：IEEE 802.3以太網。以太網使用各種介質類型，從同軸電纜到雙絞銅纜和光纖電纜（在較早的模塊中討論）。 802.3以太網標準和使用幀在包括無線802.11在內的各種媒體上進行通信的概念如今非常盛行，了解以太網的基本知識（包括每個標準對我們網絡的各種速度和距離限制）至關重要。
The original 802.3 Ethernet standard sent data over coaxial cables at a half-duplex transmission rate which means devices can only transmit (TX) or Receive (RX) alternately at separate intervals because the data used the same path for both. This is analagous to communicating using a walkie-talkie rather than a telephone.
最初的802.3以太網標準以半雙工傳輸速率通過同軸電纜發送數據，這意味著設備只能以單獨的間隔交替（TX）或接收（RX），因為這兩個數據使用相同的路徑。這類似於使用對講機而不是電話進行通話。
This coaxial cable design became known as Thicknet and later Thinnet due to the size of the cables and was mostly used in bus and ring network topologies.
由於電纜的尺寸，這種同軸電纜設計被稱為Thinnet，後來被稱為Thinnet，並且主要用於總線和環形網絡拓撲中。
Thicknet, the original IEEE 802.3 standard designated as 10Base5, provided a maximum bandwidth of 10Mbps and was limited in distance to 500 meters. Thinnet, or IEEE 10Base2, used a smaller type of coaxial and also provided a maximum bandwidth of 10 Mbps, but was limited to 185 meters. Eventually the industry transitioned from coaxial cabling to unshielded twisted-pair cabling.
最初被指定為10Base5的IEEE 802.3標準Thicknet提供的最大帶寬為10Mbps，並且距離限制為500米。 Thinnet或IEEE 10Base2使用較小類型的同軸電纜，並且提供的最大帶寬為10 Mbps，但限制為185米。最終，該產業從同軸電纜過渡到非屏蔽雙絞線電纜。
Twisted pair cabling, dubbed 10BaseT, provided the same 10 Mbps half-duplex maximum bandwidth with a category 3 cable, but the distance was limited to 100 meters due to the lack of the extra shield that coaxial provided. In spite of the increased attenuation (loss of signal strength over distance), network designers moved to twisted pair cabling because of ease of installation and overall lower cost. Coaxial cable fell out of favor and the 802.3 Ethernet standard continues to evolve with faster data rates over twisted pair cabling categories.
雙絞線電纜（稱為10BaseT）與第3類電纜可提供相同的10 Mbps半雙工最大帶寬，但由於缺少同軸電纜提供的額外屏蔽，因此距離限制為100米。儘管衰減增加了（信號強度隨距離損失），但由於易於安裝和總體成本較低，網絡設計人員仍選擇雙絞線佈線。同軸電纜不受歡迎，並且802.3以太網標準繼續發展，而雙絞線電纜類別的數據速率更快。
The design question that Ethernet had to answer was how a device should access the network. The nature of half-duplex transmission (TX or RX) over a single wire pair meant that collisions were imminent. Should the access be deterministic and orderly, or contention-based and chaotic? The older ring-based networks, such as token ring, were developed upon the premise that order was necessary: each machine would wait for its turn to transmit its data until it received the electronic token that was passed around the ring. This is similar to the “talking stick” or “speaker’s staff” used by Native Americans and other aboriginal tribes where the staff (token) gave the person access to speak and the remaining group members listened. Ethernet, on the other hand, is premised upon a contention-based model. This is more chaotic and allows any device on the network to transmit anytime it wishes. The problem with this type of philosophy is figuring out how to prevent two devices from transmitting at the same time and causing a collision of the data. With Ethernet, the answer came in the form of a media access control method called carrier sense multiple access/collision detect (CSMA/CD).
以太網必須回答的設計問題是設備如何訪問網絡。單線對上半雙工傳輸（TX或RX）的性質意味著即將發生衝突。訪問應該是確定性和有序的，還是基於競爭且混亂的？較早的基於環的網絡（例如令牌環）是在必須有順序的前提下開發的;每台機器都將等待其輪流發送其數據，直到接收到圍繞環傳遞的電子令牌為止。這類似於美洲原住民和其他原住民部落使用的“說話棒”或“發言人的工作人員”，其中工作人員（令牌）使該人員可以發言，其餘的小組成員則可以收聽。另一方面，以太網以基於競爭的模型為前提。這更加混亂，並允許網絡上的任何設備在其希望的任何時間進行傳輸。這種類型原理存在的問題是，要弄清楚如何防止兩個設備同時傳輸並導致數據衝突。對於以太網，答案是以一種稱為載波偵聽多路訪問/衝突檢測（CSMA / CD）的媒體訪問控制方法。
PCH 12 Ethernet Standards(以太網標準) <<
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