Overview of Ethernet

Overview

Ethernet technology originated from an experimental network on which multiple PCs were connected at 3 Mbit/s. In general, Ethernet refers to a standard connection for 10 Mbit/s Ethernet networks. The Digital Equipment Corporation (DEC), Intel, and Xerox joined efforts to develop and then issue Ethernet technology in 1982. The IEEE 802.3 standard is based on and compatible with the Ethernet standard.

In TCP/IP, the encapsulation format of IP packets of Ethernet and the IEEE 802.3 network is defined in RFC standard. Currently, the most commonly-used encapsulation format is Ethernet_II which is also called Ethernet DIX.

To distinguish Ethernet frames of these two types, in this document Ethernet frames of Ethernet are called Ethernet_II frames; Ethernet frames of IEEE802.3 network are called IEEE 802.3 frames.

Purpose

Ethernet and token ring networks are typical local area network (LANs).

Ethernet has become the most important LAN networking technology because it is flexible, simple, and easy to implement.

• Shared Ethernet

  Initially, Ethernet networks were shared networks with 10M Ethernet technology. Ethernet networks were constructed with coaxial cables, and computers and terminals were connected through intricate connectors. This structure is complex and only suitable for communications in half-duplex mode because only one line exists.

  In 1990, 10BASE-T Ethernet based on twisted pair cables emerged. In this technology, terminals are connected to a hub through twisted pair cables and communicate through a shared bus in the hub. The structure is physically a star topology. CSMA/CD is still used because inside the hub, all terminals are connected to a shared bus.

  All the hosts are connected to a coaxial cable in a similar manner. When a large number of hosts exist, the following problems arise:

  • Reliability of the media is low.

  • Media access conflicts are severe.

  • Packets are not properly broadcast.

  • Security is not ensured.

• 100M Ethernet

  100M Ethernet works at a higher rate (10 times the rate of 10M Ethernet) and differs from 10M Ethernet in the following ways:

  • Network type: 10M Ethernet supports only a shared Ethernet, while 100M Ethernet is a 10M/100M auto-sensing Ethernet and can work in half-duplex or full-duplex mode.

  • Negotiation mechanism: 10M Ethernet uses Normal Link Pulses (NLPs) to detect the link connection status, while 100M Ethernet uses auto-negotiation between two link ends.

• Gigabit Ethernet (GE) and 10GE

  With the advancement of computer technology, applications such as large-scale distributed databases and high-speed transmission of video images emerged. Those applications require high bandwidth, and traditional 100M Fast Ethernet (FE) cannot meet the requirements. GE was introduced to provide higher bandwidth.

  GE inherits the data link layer of traditional Ethernet. This protects earlier investments in traditional Ethernet. The GE and traditional Ethernet have different physical layers, however, to transmit data at 1000 Mbit/s, the GE uses optical fiber channels.

  As computer science develops, the 10GE technology becomes mature and is widely used on Datacom backbone networks. This technology is also used to connect high-end database servers.