DCE

The success of the original Ethernet project lead to a joint development of a 10 Mbps standard in 1980. This time three companies were involved: Digital Equipment Corporation, Intel and Xerox. The Ethernet Version 1 specification that arose from this development formed the basis for the first IEEE 802.3 standard that was approved in 1983, and finally published as an official standard in 1985. Since these first standards were written and approved, a number of revisions have been undertaken to update the Ethernet standard and keep it in line with the latest technologies that are becoming available.

Ethernet standard releases

The Ethernet standard has undergone many releases and updates as a result of the continual development of the technology. In this way, Ethernet has been able to meet the ongoing needs of the industry.

Ethernet terminology

There is a convention for describing the different forms of Ethernet. For example 10Base-T and 100Base-T are widely seen in the technical articles and literature. The designator consists of a three parts:
The first number (typically one of 10, 100, or 1000) indicates the transmission speed in megabits per second.

The second term indicates transmission type: BASE = baseband; BROAD = broadband.

The last number indicates segment length. A 5 means a 500-meter (500-m) segment length from original Thicknet. In the more recent versions of the IEEE 802.3 standard, letters replace numbers. For example, in 10BASE-T, the T means unshielded twisted-pair cables. Further numbers indicate the number of twisted pairs available. For example in 100BASE-T4, the T4 indicates four twisted pairs.


Elements

The Ethernet LAN can be considered to consist of two main elements: the interconnecting media, and the network nodes.

The network nodes themselves fall into two categories. The first is the Data Terminal Equipment (DTE). These devices are either the source or destination of the data being sent. Devices such as PCs, file servers, print servers and the like fall into this category. The second category of devices are known as Data Communications Equipment (DCE). Devices that fall into this category receive and forward the data frames across the network, and they may often be referred to as 'Intermediate Network Devices' or Intermediate Nodes. They include items such as repeaters, routers, switches or even modems and other communications interface units.

The media through which the signals propagate are just as important. Initially coaxial cable with a single inner connector were used. Now either an Unshielded Twisted Pair (UTP) or a Shielded Twisted Pair (STP) are normally used. There are also optical fibre options, and these are often used for the much higher data rate systems.

Network topologies

There are several network topologies that can be used for Ethernet communications. The actual form used will depend upon the requirements.

Point to point - This is the simplest configuration as only two network units are used. It may be a DTE to DTE, DTE to DCE, or even a DCE to DCE. In this simple structure the cable is known as the network link. Links of this nature are used to transport data from one place to another and where it is convenient to use Ethernet as the transport mechanism.

Coaxial bus - This type of Ethernet network is rarely used these days. The systems used a coaxial cable where the network units were located along the length of the cable. The segment lengths were limited to a maximum of 500 metres, and it was possible to place up to 1024 DTEs along its length. This form of network is not used these days, although a very few legacy systems might just still be in use.

Star network - This type of Ethernet network has been the dominant topology since the early 1990s. It consists of a central network unit, which may be what is termed a multiport repeater or hub, or a network switch. All the connections to other nodes radiate out from this and are point to point links.