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Ethernet
ETHERNET
Definiton: Ethernet is a physical and data link layer technology for LAN networking. When it first began to be widely deployed in the 1980s, Ethernet supported a maximum theoretical data rate of 10 megabits per second (Mbps). More recently, Fast Ethernet standards have extended traditional Ethernet technology to 100 Mbps peak, and Gigabit Ethernet technology extends performance up to 1000 Mbps. Higher level network protocols like IP use Ethernet as their transmission medium. Data travels over Ethernet in the form of frames, and collisions can occur when multiple devices on the line attempt to transmit simultaneously. The run length of Ethernet cables is limited (to roughly 100 meters), but various special-purpose devices exist that make Ethernet a cost-effective option for networking an entire large school or office building. Related Resources: INTRODUCTION ETHERNET Still the technology of choice for many types of networks Ethernet has been a relatively inexpensive, reasonably fast, and very popular LAN technology for several decades. Two individuals at Xerox PARC -- Bob Metcalfe and D.R. Boggs -- developed Ethernet beginning in 1972 and specifications based on this work appeared in IEEE 802.3 in 1980. Ethernet specifications define low-level data transmission protocols and the technology needed to support them. In the OSI model, Ethernet technology exists at the physical and data link layers (layers 1 and 2). A low-level network technology, Ethernet supports IP and most other higher-level protocols. Traditional Ethernet supports data transfers at the rate of 10 Megabits per second (Mbps). Over time, as the performance needs of LANs have increased, related technologies like Fast Ethernet and Gigabit Ethernet have been developed that extend traditional Ethernet to 100 Mbps and 1000 Mbps speeds, respectively. Traditional Ethernet Often referred to as "Thicknet," 10Base5 technology was the first incarnation of Ethernet. It was used in the 1980s until 10Base2 "Thinnet" with more flexible cabling appeared. (At five millimeters, Thinnet is one-half the thickness of Thicknet.) The most common form of traditional Ethernet, however, is 10Base-T due to the inherent advantages of unshielded twised pair (UTP) over coaxial cabling and its low cost compared to alternatives like fiber. The following table lists these well-known forms of Ethernet technology. Besides the type of cable involved, another important factor in Ethernet networking is the segment length. A single uninterrupted network cable can only span a certain physical distance before its electrical characteristics are critically affected by factors such as line noise or reduced signal strength. Name Segment Length (Max.) Cable 10Base5 500m / 1640ft. RG-8 or RG-11 coaxial 10Base2 185m / 606ft. RG 58 A/U or RG 58 C/U coaxial 10Base-T 100m / 328ft. Category 3 or better unshielded twisted pair Several other less well-known Ethernet standards exist, including 10Base-FL, 10Base-FB, and 10Base-FP for fiber optic networks and 10Broad36 for broadband (CATV) cabling. Fast Ethernet In the mid-1990s, Fast Ethernet achieved its design goal of increasing the performance of traditional Ethernet while avoiding the need to completely re-cable existing networks. Fast Ethernet comes in two major varieties: • 100Base-T (using unshielded twisted pair cable) • 100Base-FX (using fiber optic cable) By far the most popular of these is 100Base-T, a standard that includes 100Base-TX (Category 5 UTP), 100Base-T2 (Category 3 or better UTP), and 100Base-T4 (100Base-T2 cabling modified to include two additional wire pairs). Gigabit Ethernet Wheareas Fast Ethernet improved traditional Ethernet from 10 Megabit to 100 Megabit speed, Gigabit Ethernet offers the same order-of-magnitude improvement over Fast Ethernet by offering speeds of 1000 Megabits (1 Gigabit). Gigabit Ethernet was first made to travel over optical and copper cabling, but the 1000Base-T standard successfully supports it as well. 1000Base-T uses Category 5 cabling similar to 100 Mbps Ethernet, although achieving gigabit speed requires the use of additional wire pairs. Ethernet In Use An Ethernet network functions nearly identically no matter its speed or layout. Devices plugged into the network typically possess a network interface card (NIC) -- more generally, a network adapter -- that interfaces directly to the system bus. The NIC includes a cable connector such as the RJ-45 connector used with modern telephones. (Original versions of Ethernet used very different connectors, though). Data sent over the Ethernet exists in the forms of frames. An Ethernet frame contains two headers and a data section having a combined length of no more than 1518 bytes. The standard calls for frames to be broadcast to all devices, meaning that network adapters must explicitly recognize and discard all frames that were not intended to be received by them. Devices wanting to transmit on the Ethernet first perform a very fast check to determine whether the medium is available or whether a transmission is currently in progress; if the Ethernet is available, the device transmits. However, the Ethernet standard does not prevent multiple devices from transmitting simulatenously. These so-called collisions cause both transmission to fail and require both devices to re-transmit at a later time. A specialized algorithm is used with Ethernet to determine the proper waiting time between re-transmissions. As mentioned above, Ethernet cables are limited in their reach, and these distances (as short as 100 meters) are insufficient to cover medium-sized and large workgroups. A repeater in Ethernet networking is a device that allows multiple cables to be joined and greater distances to be spanned. One popular type of repeater device is an Ethernet hub. Conclusion Ethernet is one of the Internet's foundation technologies. Despite its advanced age, Ethernet continues to power many of the world's local area networks and grow for the future |
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| Konu | Konuyu Başlatan | Forum | Yanıt | Son Mesaj |
| Ethernet | PCkopat | Zanisti | 1 | 11-05-2007 04:25 PM |
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| Gigabit Ethernet | HEWALZAZA | Bilgisyar Donanım Desteği | 1 | 03-05-2007 11:04 AM |
| Gigabit Ethernet Teknolojisi | PCkopat | Bilgisyar Donanım Desteği | 1 | 01-02-2007 11:45 AM |
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