Ethernet is a widely used Local Area Network (LAN) technology that controls how information is transmitted on the network through cables. The concept can be demonstrated using a civil discussion forum, whereby group members do not interrupt the member who is talking. The original Ethernet envisaged communication over a single cable shared by all cables in the network, so that once a device was connected to the cable, it could communicate with the cable. The network can “welcome” other devices which get attached to the cable without any modification necessary for those devices that are already on the network. Ethernet as a LAN technology involved networks in close proximity, though recent technologies make it possible to have networks spanning over several kilometers. Ethernet has some basic rules that its operations are premised on. There are also several terminologies that are mostly used by the cognoscenti. The concept of medium refers to a path on which electronic signals travel. This used to be a coaxial copper cable but these days it is mostly fiber optic cable. Segment refers to a single shared medium as an Ethernet segment. Node refers to each of the devices that attach to the segment. The short messages that are exchanged by nodes as a means of communication are called frames.

Ethernet Frames

The Ethernet protocol defines a set of rules to be followed when constructing frames, which can be equated with sentences in case of human beings. For instance, certain pieces of information must be present in a frame. A frame must have a source address as well as a destination address to identify the sender and the recipient of the information. The addresses identify nodes, almost the same way a physical address identifies a particular place. Any two devices on the Ethernet network should not have the same address. We have already seen the importance of the destination address. It happens that the signals on the Ethernet reach every node, and so every device on the network receives the frames sent. However, since the frames have a destination address, the device examines and finds out whether the piece of information was intended for it, and if it was not, the well-behaved device eventually discards the frame without even looking at the contents.

Carrier Sense

Another concept present in the Ethernet protocol is called “carrier sense”. Just like a polite person will not interrupt another in a conversation, a device will not transmit frames if another device on the network is transmitting frames on the medium. If the medium is idle the device then determines that time is appropriate to send the signal.

Ethernet Limitations

One limitation of Ethernet is that it depends too much on cables which limit the length that one can have between different devices and the overall network length. Although electrical signals propagate through the cable very fast, they tend to weaken as they travel. In addition, there are practical limits to the number of devices you can link on Ethernet. Just like too many people in a discussion room, each single person may have to wait too long a time before being allowed to speak. Likewise, devices will have to wait too long to transmit frames.

For more information on Ethernet read What is Ethernet?