Ethernet Network Technology
Engineers Bob Metcalfe and D.R. Boggs developed Ethernet beginning in 1972. Industry standards based on their work were established in 1980 under the IEEE (Institute of Electrical and Electronics Engineers) 802.3 set of specifications. Ethernet specifications define low-level data transmission protocols and the technical details manufacturers need to know to build Ethernet products such as cards and cables. Ethernet technology has evolved and matured in the years since. Nowadays, the consumer can rely on off-the-shelf Ethernet products to work as designed and to work with each other.
Traditional Ethernet supports data transfers at a rate of 10 megabits per second (Mbps). As the performance needs of networks increased over time, the industry created additional Ethernet specifications for Fast Ethernet and Gigabit Ethernet. Fast Ethernet extends traditional Ethernet performance up to 100 Mbps, and Gigabit Ethernet, up to 1000 Mbps. Although they aren't yet available to the average consumer, 10 Gigabit Ethernet (10,000 Mbps) now powers the networks of some businesses, data centers, and Internet2 entities. Generally, however, expense is the factor limiting its widespread adoption. Ethernet cables likewise are manufactured to any of several standard specifications. The most popular Ethernet cable in use, Category 5 (CAT5 cable) supports both traditional and Fast Ethernet. Category 5e (CAT5e) and CAT6 cables support Gigabit Ethernet.
To connect an Ethernet cable to a computer (or other network devices), you plug a cable directly into the device's Ethernet port. Some devices without Ethernet support can support Ethernet connections via dongles such as USB-to-Ethernetadapters. Ethernet cables use connectors that look much like the RJ-45 connector used with traditional telephones.
Often referred to as Thicknet, 10Base5 was the first incarnation of Ethernet technology. The industry used Thicknet in the 1980s until 10Base2 Thinnet appeared. Compared to Thicknet, Thinnet offered the advantage of thinner (5 millimeters vs. 10 millimeters) and more flexible cabling, making it easier to wire office buildings for Ethernet. The most common form of traditional Ethernet, however, was 10Base-T. It offers better electrical properties than Thicknet or Thinnet, because 10Base-T cables use unshielded twisted pair (UTP) wiring rather than coaxial. 10Base-T also proved more cost-effective than alternatives such as fiber optic cabling. Numerous other lesser-known Ethernet standards exist, including 10Base-FL, 10Base-FB, and 10Base-FP for fiber optic networks and 10Broad36 for broadband (cable television) cabling. Fast and Gigabit Ethernet have made all of the above traditional forms, including 10Base-T, obsolete.
In the mid-1990s, Fast Ethernet technology matured and met its design goals of:
Fast Ethernet comes in two major varieties:
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).
While Fast Ethernet improved traditional Ethernet from 10-Megabit to 100-Megabit speed, Gigabit Ethernet boasts 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 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.
Traditional Ethernet employs a bus topology, meaning that all devices or hosts on the network use the same shared communication line. Each device possesses an Ethernet address, also known as MAC address. Sending devices use Ethernet addresses to specify the intended recipients of messages.
Data sent over Ethernet exists in the form of frames. An Ethernet frame contains a header, a data section, and a footer with a combined length of no more than 1,518 bytes. The Ethernet header contains the addresses of both the intended recipient and the sender. Data sent over the Ethernet is automatically broadcast to all devices on the network. By comparing the Ethernet address against the address in the frame header, each Ethernet device tests each frame to determine if it was intended for it and reads or discards the frame as appropriate. Network adapters incorporate this function into their hardware.
Devices wanting to transmit on an Ethernet network first perform a preliminary check to determine whether the medium is available or a transmission is in progress. If the Ethernet is available, the sending device transmits onto the wire. It's possible, however, that two devices will perform this test at approximately the same time and both transmit simultaneously. By design, as a performance tradeoff, the Ethernet standard does not prevent multiple simultaneous transmissions. These so-called collisions, when they occur, cause both transmissions to fail and require both sending devices to retransmit. Ethernet uses an algorithm based on random delay times to determine the proper waiting period between retransmissions. The network adapter also implements this algorithm.
In traditional Ethernet, this protocol for broadcasting, listening, and detecting collisions is known as CSMA/CD (carrier sense multiple access/collision detection). Some newer forms of Ethernet do not use CSMA/CD. Instead, they use the full-duplex Ethernet protocol, which supports point-to-point simultaneous sending and receiving with no listening required.
As mentioned earlier, Ethernet cables are limited in their reach, and those distances (as short as 100 meters) are insufficient to cover medium and large network installations. A repeater in Ethernet networking allows multiple cables to be joined and greater distances to be spanned. A bridge device can join an Ethernet to another network of a different type, such as a wireless network. One popular type of repeater device is an Ethernet hub. Other devices sometimes confused with hubs are switches and routers. Ethernet network adapters also exist in multiple forms. Computers and game consoles feature built-in Ethernet adapters. USB-to-Ethernet adapters and wireless Ethernet adapters also can be configured to work with many devices.
Ethernet is one of the Internet's key technologies. Despite its advanced age, Ethernet continues to power many of the world's local area networks and continually improves to meet future needs for high-performance networking.