Networking Technologies Overview

Networking Technologies Overview

Ethernet has been around since the late 1970s and remains

the leading network technology for local-area networks

(LANs). (A LAN is a network contained in a building or

on a single campus.) Ethernet is based on carrier sense

multiple access with collision detection (CSMA/CD). (See

the margin note on Token Ring for another basic style

of network communication.)

Simply put, an Ethernet workstation can send data

packets only when no other packets are traveling on the

network, that is, when the network is “quiet.” Otherwise,

it waits to transmit, just as a person might wait for another

to speak during conversation.

If multiple stations sense an opening and start sending

at the same time, a “collision” occurs. Then, each station

waits a random amount of time and tries to send its packet

again. After 16 consecutive failed attempts, the original

application that sent the packet has to start again. As more

people try to use the network, the number of collisions,

errors, and subsequent retransmits grows quickly, causing

a snowball effect.

Collisions are normal occurrences, but too many

can start to cause the network to slow down. When more

than 50 percent of the network’s total bandwidth is used,

collision rates begin to cause congestion. Files take longer

to print, applications take longer to open, and users are

forced to wait. At 60 percent or higher bandwidth usage,

the network can slow dramatically or even grind to a halt.