The Ethernet topology was developed at the University of Hawaii to connect computers on the various Islands. It was radio based design. Ethernet is one of the most popular Computer Network or LAN technologies in use today covering more than 85% of the computer networks. Ethernet system consists of three basic elements:
1. The physical medium use to carry Ethernet signals between computers on the network
2. A set of rules (protocols) embedded in each Ethernet interface that will decide how multiple computers on the network will have access to the data on the medium.
3. An Ethernet frame that consists of a standardized set of bits used to carry data over the system.
The operation of Ethernet can be described in simple terms as follows:
Each computer on the Ethernet Network, also known as a node, operates independently of all other nodes. All nodes attached to an Ethernet are connected to a shared medium over which the Ethernet signals travel serially, one data bit at a time.
To send data a station first listens to the channel and when the channel is idle the station transmits its information in the form of an Ethernet frame, or packet. The Ethernet rules (protocol) are defined in such a way that every node gets a fair amount of frame transmission opportunity.
As each Ethernet frame is sent out on the shared medium, the Ethernet interfaces inside the node look at the destination address. The interfaces compare the destination address of the frame with their own address. The Ethernet interface with the same address as the destination address in the frame will read the entire frame and all other network interfaces will ignore the information.
Medium Access Control of Ethernet
The set of rules which ensures that every node in an Ethernet gets a fair amount of frame transmission opportunity, are called the "Medium Access Control" mechanism. The Medium Access Control mechanism is based on a system called Carrier Sense Multiple Access with Collision Detection (CSMD/CD).
Ethernet Frame.
The heart of Ethernet system is the Ethernet Frame, which is used to deliver information between the computers. The frame consists of a set of bits organized into several fields. These fields include address fields, a data field and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact.
Advantages of Ethernet.
Ethernet's major advantages are:
1. It is an inexpensive way to achieve high speed LAN transmissions (10 to 100 MB/s)
2. It is a proven technology that supports various writing configurations.
3. It works well with a large number of LAN and micro-to-mainframe applications.
4. It is easy to install.
Disadvantages of Ethernet Cabling
The Ethernet cabling ahs the following disadvantages:
1. Ethernet is not a high-level performer in high-load environments. This protocol (CSMA/CD: Carrier Sense Multiple Access/Collision Detection) can slow down dramatically if hundreds of workstations are competing for the same cabling trunk
2. Its linear bus cabling system can sometimes make it difficult to isolate problems.
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