What is Ethernet?

In the early 1980s, Digital Equipment Corporation, Intel, and Xerox developed the Ethernet Local Area Networking format. This technology was soon accepted by the IEEE Committee, creating the 802.3 standard. This standard dictates the use of CSMA/CD (Carrier Sense Multiple Access with Collision Detection) as its accessing scheme. Networks use a variety of NICs (Network Interface Cards), hubs, transceivers, converters, repeaters & switches, as well as different types of transmission media for carrying signals.

• Accessing Scheme: CSMA/CD - Carrier sense multiple access with Collision Detection.
• Speed: 10 Mbps/100 Mbps/1000 Mbps (1 GBps).
• Network Architecture: Coax Bus, UTP Star, Fiber Star

1. Ethernet operational theory is quite easy to understand and a simple analogy is helpful to visualise the basics. Imagine a long hallway lined with offices. The hallway represents the physical network, the offices represent the attached stations. When an occupant wishes to speak to another occupant they would lean into the hallway, listen to make sure no one else is engaging in a conversation, then speak out addressing the desired recipient. All other occupants hear the conversation but ignore it knowing it is not directed to them.
   In essence, the above analogy describes the medium access method standardised under IEEE802.3 known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD). Carrier Sense is analogous to the ability to listen to all conversations (network traffic). Multiple Access is the ability for multiple users to access the medium while data is transmitted.
2. Returning to our analogy, what if two or more occupants decide to speak at the same time? Naturally the overlapping voices would become garbled and indistinguishable. With Ethernet this is known as a collision. In the CSMA/CD method, CD stands for Collision Detection. If a collision is detected by a transmitting station(s) the rule states: stop transmitting immediately, transmit a jamming signal to inform all other stations to stop, then wait a random period (binary exponential backoff) and re-transmit.
   Unfortunately, as the quantity of stations increases so does the amount of collisions. This causes the average access time to increase proportionally. This is referred to in the industry as network congestion.
3. Fortunately, there are several ways to alleviate network congestion. One way is that the entire network can be upgraded to Fast Ethernet (100 Mbps) which represents a 10 fold increase in transmission speed. This, however requires upgrading of all components and can be rather expensive. Another approach is to add an Ethernet Switch.
   In the above analogy, the long hallway represents the network. Adding a two port switch is analogous to dividing the hallway into two shorter hallways separated by a door. This creates two segments (collision domains) where messages that are directed for occupants within the same area are not allowed to pass through the door. Only when a message is directed to another segment does the door open allowing the message to pass.
   An Ethernet switch reduces collisions by creating multiple collision domains. This, in most cases, is the most economical approach. A switch can be added to any network without the need to upgrade existing equipment.