Introduction to Ethernet
A local area network developed by Xerox in 1976, originally for linking minicomputers at the Palo Alto Research Centre. A widely implemented network from which the IEEE 802.3 standard for contention networks was developed, Ethernet uses a bus topology and relies on the form of access known as CSMA/CD to regulate traffic on the main communication line. Network nodes are connected by coaxial cable (in either of two varieties, known as thin and thick) or by twisted-pair wiring. Thin Ethernet cabling is 5 millimetres (about 0.4 inch) in diameter and can connect network stations over a distance of 300 meters (about 1000 feet); thick Ethernet cabling is 1 centimetre (about 0.4 inch) in diameter and can connect stations up to 1000 meters (about 3300 feet) apart. Information on an Ethernet network is sent in variable-length frames containing delivery and control information plus up to 1500 bytes of data. The original Ethernet standard provides for baseband transmission at 10 megabits (10 million bits) per second.
Advantages of Ethernet
Ethernet networks offer the following advantages:
- Good for networks in which traffic is heavy only occasionally or in which traffic consists of a few long transmissions.
- Easy to install.
- Technology is well known and thoroughly tested.
- Moderate costs.
- Flexible cabling, especially when using twisted-pair cable.
Disadvantages of Ethernet
Ethernet networks have the following disadvantages:
- Heavy traffic can slow down a network that uses a contention access system such as CSMA/CD.
- Since all nodes are connected to the main cable in most Ethernet networks, a break in this cable can bring down the entire network.
- Troubleshooting is more difficult with a bus topology.
- Room for incompatibilities because of frame structure (such as 802.3 versus Blue Book Ethernet).
Types of Ethernet Networks
Type Description 10Base2 Thin Ethernet using thin (3/16-inch), 50-ohm coaxial cable. This is arguably the most popular Ethernet configuration. 10Base5 Thick Ethernet using thick (3/8-inch), 50-ohm coaxial cable. Although it's the cabling for Blue Book Ethernet, this is not a very popular configuration because thick coaxial cable is difficult to handle and install. 10BaseT Twisted-pair Ethernet using UTP cable. This configuration was adopted as the 802.3I standard in 1990, and it is becoming popular because UTP is inexpensive and easy to install and work with. 1Base5 The StarLAN network developed by AT&T. StarLAN uses UTP cable and a star topology, and was defined long before the 10BaseT standard was proposed. 10Broad36 The only network in the 802.3 standard. This network uses 75-ohm coaxial cable (CATV cable). 10BaseF The only network in the 802.3 standard that explicitly calls for fiber-optic cable. This type is actually divided into three variations: 10BaseFB, 10BaseFP and 10BaseFL. 10BaseFB This network uses optical fiber for the backbone, or trunk, cable. Trunk segments can be up to 2 kilometers (1.25 miles) in length. 10BaseFP This specifies a network that uses optical fiber and a star topology. The coupler used to distribute the signal is passive (does not regenerate the signal before distributing). As a result, such a network needs no electronics except for those in the computer. Maximum length for a piece of such cable is 500 meters (1650 feet). 10BaseFL This specifies a network that uses optical fiber to connect a node to a hub, or concentrator. Cable segments can be up to 2 kilometers in length. 10BaseVG A 100 Mbps Ethernet network developed by Hewlett-Packard and AT&T Microelectronics. 100BaseT A 100 Mbps Ethernet network developed by Grand Junction Networks. This is a proposed standard of the IEEE 802.3 study group. Variants include 100BaseT4, 100BaseTX, and 100BaseFX.
Copyright © 1998.