Articles Tagged ‘Ethernet’

100Base-(T) TX/T4/FX - Ethernet

100Base-(T) TX/T4/FX - EthernetThe 100Base-TX (sometimes referred to 100Base-T) cable was until 2010 perhaps the most popular cable around since it has actually replaced the older 10Base-T and 10Base-2 (Coaxial). The 100Base-TX cable provides fast speeds up to 100Mbits and is more reliable since it uses CAT5e cable (see the CAT 1/2/3/4/5 page).There is also 100Base-T4 and 100Base-FX available, which we discuss at the end of this article.

So what does 100Base-TX/T4/FX mean?

We are going to break the "100Base-T" into three parts so we can make it easier to understand:


The number 100 represents the frequency in MHz (Mega HertZ) for which this cable is made. In this case it is 100 MHz. The greater the MHz, the greater speeds the cable can handle. If you try to use this type of cable for greater frequencies (and, therefore, speeds) it will either not work or become extremely unreliable. The 100 MHz speed translates to 100Mbit per second, which in theory means 12 Mbps. In practice though, you wouldn't get more than 4 Mbps.

Early Communication Technology - Morse Code and Ethernet

We tend to think of digital communication as a new idea but in 1844 a man called Samuel Morse sent a message 37 miles from Washington D.C. to Baltimore, using his new invention ‘The Telegraph’. This may seem a far cry from today's computer networks but the principles remain the same.

Morse code is type of binary system which uses dots and dashes in different sequences to represent letters and numbers. Modern data networks use 1s and 0s to achieve the same result. The big difference is that while the telegraph operators of the mid 19th Century could perhaps transmit 4 or 5 dots and dashes per second, computers now communicate at speeds of up to 1 Giga bit, or to put it another way, 1,000,000,000 separate 1s and 0s every second.


Figure 1. Morse Code device used to transmit '0' and '1'

Although the telegraph and the teletypewriter were the forerunners of data communications, it has only been in the last 35 years that things have really started to speed up. This was borne out of the necessity for computers to communicate at ever ncreasing speeds and has driven the development of faster and faster networking equipment, higher and higher specification cables and connecting hardware.

Development of New Network Technology

Ethernet Frame Formats

Analysis of Ethernet Frame Formats

An understanding of the basics of the Ethernet Frame Format is crucial to any discussion of Ethernet technology.

In this section, we will discuss:

  1. The four different frame formats used in the Ethernet world; the purpose of each of the fields in an Ethernet frame; the reasons that there are so many different versions of the Ethernet Frame Format - Ethernet, Ethernet, Ethernet, or Ethernet?! When somebody tells me that they are running Ethernet on their network, I inevitably have to ask: "Which Ethernet?". Currently, there are many versions of the Ethernet Frame Format in the commercial marketplace, all subtly different and not necessarily compatible with each other.
  2. The explanation for the many types of Ethernet Frame Formats currently on the marketplace lies in Ethernet's history. In 1972, work on the original version of Ethernet, Ethernet Version 1, began at the Xerox Palo Alto Research Center. Version 1 Ethernet was released in 1980 by a consortium of companies comprising DEC, Intel, and Xerox. In the same year, the IEEE meetings on Ethernet began. In 1982, the DIX (DEC/Intel/Xerox) consortium released Version II Ethernet and since then it has almost completely replaced Version I in the marketplace. In 1983 Novell NetWare '86 was released, with a proprietary frame format based on a preliminary release of the 802.3 spec. Two years later, when the final version of the 802.3 spec was released, it had been modified to include the 802.2 LLC Header, making NetWare's proprietary format incompatible. Finally, the 802.3 SNAP format was created to address backwards compatibility issues between Version 2 and 802.3 Ethernet.

As you can see, the large number of players in the Ethernet world has created a number of different choices. The bottom line is this: either a particular driver supports a particular frame format, or it doesn't. Typically, Novell stations can support any of the frame formats, while TCP/IP stations will support only one although there are no hard and fast rules in Networking.


Ethernet Frame Formats

The following sections will outline the specific fields in the different types of Ethernet frames. Throughout the section, we will refer to fields by referencing their "offset" or number of bytes from the start of the frame beginning with zero. Therefore, when we say that the destination address field is from offset zero through five we are referring to the first six bytes of the frame.


The Preamble

Regardless of the frame type being used, the means of digital signal encoding on an Ethernet network is the same. While a discussion of Manchester Encoding is beyond the scope of this page, it is sufficient to say that on an idle Ethernet network, there is no signal. Because each station has its own oscillating clock, the communicating stations have to have some way to "synch up" their clocks and thereby agree on how long one bit time is. The preamble facilitates this. The preamble consists of 8 bytes of alternating ones and zeros, ending in 11.

A station on an Ethernet network detects the change in voltage that occurs when another station begins to transmit and uses the preamble to "lock on" to the sending station's clock signal. Because it takes some time for a station to "lock on", it doesn't know how many bits of the preamble have gone by. For this reason, we say that the preamble is "lost" in the "synching up" process. No part of the preamble ever enters the adapter's memory buffer. Once locked on, the receiving station waits for the 11 that signals that the Ethernet frame follows.

Most modern Ethernet adapters are guaranteed to achieve a signal lock within 14 bit-times.

The Different "Flavors" of Ethernet

While the preamble is common to every type of Ethernet, what follows it is certainly not. The major types of Ethernet Frame Format are:

FRAME TYPE Novell calls it: Cisco calls it:
Novell Proprietary ("802.3 Raw")   ETHERNET_802.3 NOVELL

 As you examine the table above please note that an IEEE 802.3 frame is referred to as an 802.2 frame by Novell. The frame that Novell refers to as "802.3 Raw" or "Ethernet_802.3" is their own proprietary frame format.

Ethernet Protocol, CSMA/CD, Collisions

"Ethernet" is the term that is casually applied to a number of very different data link implementations.  You will hear people refer to "Ethernet" and they might be referring to the original DEC, Intel and Xerox implementation of Version 1 or Version 2 Ethernet.  This, in a sense, is the "true" definition of "Ethernet".  When the IEEE built the 802.3 standards in 1984 the term "Ethernet" was broadly applied to them as well.  Today we talk about "Gigabit Ethernet" and, although this technology bears many similarities to its predecessors, the engineering technology has changed dramatically.

Whatever you call it, this is a Data Link technology - responsible for delivering a frame of bits from one network interface to another - perhaps through a repeater, switch or bridge.

Network Cabling

Network CablingNetwork cabling is one of the most important aspects in any network infrastructure and has become increasingly critical with the introduction of newer technologies such as blade servers, virtualization, network storage devices, wireless access points and more.

Network services such as file sharing, Internet access, network printing, email, ERP systems and more, are all delivered to the end users via the network infrastructure, which usually includes switches, fiber optic links and of course UTP cabling.

This series will focus on the different type of Ethernet copper cabling specifications, speeds and caveats of each technology.

We’ll continue with the expansion of our covered topics to cover fiber optic technology and talk about the different fiber optic cables available in the market and then jump back into the past by covering various direct cable connections used to transfer data between computers. This last section will cover extensively serial, parallel, usb ports and their different specifications/versions, plus we’ll get to talk about the variety of cables used to connect between these old-technology ports.

While many might believe the last section of this series might contain information not considered useful (serial, parallel & usb ports), you’ll be amazing on how much of this information will actually come in handy at some point in the future.

All material covered includes detailed diagrams and has been checked to ensure it is as accurate as possible.


Our popular Networking section is well-known for the variety of high-quality articles covering topics such as Network Protocols, OSI Model, IPv4 & IPv6 addressing, Subnetting, Routing, Routing protocols, CIDR-Supernettting, Ethernet technologies, VLAN Networks, Virtual Trunk Protocol (VTP), Network Address Translation (NAT), Firewalls, WAN Technologies and much more.

All articles make use of our award-winning diagrams and contain illustrations aimed to help make the learning process as easy as possible no matter how complex the topic might be.

We hope you enjoy this section and manage to master all information included.

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