ETHERNET
HISTORY
The term Ethernet refers to the family of local-area
network (LAN) products covered by the IEEE 802.3 standard that defines
what is commonly known as the CSMA/CD protocol. Three data rates are currently
defined for operation over optical fiber and twisted-pair cables:
10 Mbps-10Base-T Ethernet
100 Mbps-Fast Ethernet
1000 Mbps-Gigabit Ethernet.
The original Ethernet was developed as an experimental
coaxial cable network in the 1970s by Xerox Corporation to operate with
a data rate of 3 Mbps using a carrier sense multiple access collision detect
(CSMA/CD) protocol for LANs. Success with that project attracted
early attention and led to the 1980 joint development of the 10-Mbps Ethernet Version 1.0 specification bythe three-company consortium: Digital Equipment
Corporation, Intel Corporation, and Xerox Corporation.
NETWORK ELEMENTS
Ethernet LANs consist of network nodes and interconnecting
media. The network nodes fall into two major classes:
Data terminal equipment (DTE)- Devices that are either
the source or the destination of data frames. DTEs are typically
devices such as PCs, workstations, file servers, or print servers
that, as a group, are all often referred to as end stations
Data communication equipment (DCE) -Intermediate network
devices that receive and forward frames across the network
DCEs may be either standalone devices such as repeaters network switches,
and routers, or communications interface units such as
interface cards and modems.
NETWORK TOPOLOGY
Point to Point Network
The simplest structure is the point-to-point interconnection.
Only two network units are involved, and the connection may be DTE-to-DTE, DTE-to-DCE, or DCE-to-DCE. The cable in point-to-point interconnections is
known as a network link. The maximum allowable length of the link depends
on the type of cable and the transmission method that is used.
Coaxial Bus Topology
The original Ethernet networks were implemented with
a coaxial bus structure.Segment lengths were limited to 500 meters,
and up to 100 stations could be connected to a single segment.
Individual segments could be interconnected with repeaters, as long as
multiple paths did not exist between any two stations on the network
and the number of DTEs did not exceed 1024. The total path distance
between the most-distant pair of stations was also not allowed to
exceed a maximum prescribed value.
Star connected Topology
Since the early 1990s, the network configuration of choice
has been the star-connected topology. The central network unit is either
a multiport repeater (also known as a hub) or a network switch. All connections
in a star network are point-to-point links implemented with either
twisted-pair or optical fiber cable.