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ETHERNET TECHNOLOGY

Part 1: Frames, Collisions, and 10 Mbps LANs

by James Antonakos

Start ý Ethernet Frame Format ý The Interframe Gap ý Collision Or No Collision ý Detecting Errors ý Random Waiting Period ý 10-Mbps Ethernet ý 10BaseFý Errors In Ethernet LANS ý More To Come ý Sources and PDF

This month, I begin a three-part series examining the details and operation of the popular LAN technology called Ethernet. Since its development by Xerox, Intel, and Digital Equipment Corporation in 1980, Ethernet has evolved from its initial 10-Mbps data rate, to Fast Ethernet (100 Mbps), and now Gigabit Ethernet (1000 Mbps). In this first part, I concentrate on the basic operation of 10-Mbps Ethernet. Next month, Iýll continue with Fast Ethernet and Gigabit Ethernet technology, and then complete the series with a look at the operation of hubs, switches, and routers.

IEEE STANDARD 802.3

All of the properties, procedures, and definitions associated with Ethernet are contained in the "IEEE Standard 802.3," which is a valuable addition to any library. [1] This document contains over 1200 pages and includes such information as:

• flowcharts for transmitting and receiving a bit
• signal speed, noise, and other parameters for various media
• data encoding methods (Manchester, 4B5B, etc.) used by each technology
• the method for computing the frame check sequence
• detailed discussion of collision detection
• auto-negotiation using fast link pulses
• repeater operation

Table 1 shows some of the different Ethernet technologies covered in the "IEEE Standard 802.3." The term "base," as in 10Base5, stands for baseband, a communication system that does not modulate a carrier with the information, whereas broadband network technologies (such as those used with cable modems) put the information onto one or more RF carriers.

The 10, 100, or 1000 represents the speed of the technology in megabits per second. The "5" in 10Base5 stands for 500 m, the length of a single thick-wire coaxial cable segment. The "2" in 10base2 represents a segment length of 185 m (thin-wire coax cabling). The suffixes T and FL stand for unshielded twisted pair (UTP cabling) and fiber link, respectively. UTP cables may be up to 100 m in length. Fiber links may be as long as 2000 m.

Iýll examine each technology, beginning with the 10-Mbps systems. Because each new technology must accomplish the same goal, reliable transmission of an Ethernet frame, Iýll start there.

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