Tuesday, 14 November 2017

Ethernet technologies


Ethernet technologies :---



Ethernet is a family of technologies that provides data-link and physical specifications for controlling access to a shared network medium. It has emerged as the dominant technology used in LAN networking.


Ethernet was originally developed by Xerox in the 1970s, and operated at 2.94Mbps. The technology was standardized as Ethernet Version 1 by a consortium of three companies - DEC, Intel, and Xerox, collectively referred to as DIX - and further refined as Ethernet II in 1982.


In the mid 1980s, the IEEE published a formal standard for Ethernet, defined as the IEEE 802.3 standard. The original 802.3 Ethernet operated at 10Mbps and successfully supplanted competing LAN technologies, such as Token Ring.


Ethernet has several benefits over other LAN technologies:

• Simple to install and manage

• Inexpensive

• Flexible and scalable

• Easy to interoperate between vendors



Ethernet Cabling Types:---



Ethernet can be deployed over three types of cabling:


Coaxial cabling – almost entirely deprecated in Ethernet networking

Twisted-pair cabling

Fiber optic cabling


Coaxial cable, often abbreviated as coax, consists of a single wire surrounded by insulation, a metallic shield, and a plastic sheath. The shield helps protect against electromagnetic interference (EMI), which can cause attenuation, a reduction of the strength and quality of a signal. EMI can be generated by a variety of sources, such as florescent light ballasts, microwaves, cell phones, and radio transmitters.


Coax is commonly used to deploy cable television to homes and businesses.


Two types of coax were used historically in Ethernet networks:

Thinnet

Thicknet


Thicknet has a wider diameter and more shielding, which supports greater distances. However, it is less flexible than the smaller thinnet, and thus more difficult to work with. A vampire tap is used to physically connect devices to thicknet, while a BNC connector is used for thinnet.



Twisted-pair cable consists of two or four pairs of copper wires in a plastic sheath. Wires in a pair twist around each other to reduce crosstalk, a form of EMI that occurs when the signal from one wire bleeds or interferes with a signal on another wire.

Twisted-pair is the most common Ethernet cable.


Twisted-pair cabling can be either shielded or unshielded. Shielded twisted pair is more resistant to external EMI; however, all forms of twisted-pair suffer from greater signal attenuation than coax cable.


There are several categories of twisted-pair cable, identified by the number of twists per inch of the copper pairs:


Category 3 or Cat3 - three twists per inch.

Cat5 - five twists per inch.

Cat5e - five twists per inch; pairs are also twisted around each other.

Cat6 – six twists per inch, with improved insulation.


An RJ45 connector is used to connect a device to a twisted-pair cable. The layout of the wires in the connector dictates the function of the cable.


While coax and twisted-pair cabling carry electronic signals, fiber optics uses light to transmit a signal. Ethernet supports two fiber specifications:



Ø Singlemode fiber – consists of a very small glass core, allowing only a single ray or mode of light to travel across it. This greatly reduces the attenuation and dispersion of the light signal, supporting high bandwidth over very long distances, often measured in kilometers.



Ø Multimode fiber – consists of a larger core, allowing multiple modes of light to traverse it. Multimode suffers from greater dispersion than single mode, resulting in shorter supported distances.


Singlemode fiber requires more precise electronics than multimode, and thus is significantly more expensive. Multimode fiber is often used for high-speed connectivity within a datacenter.