Technology Basics
3-2
Ethernet
Theory
Ethernet, in its basic form, operates like a series of offices arranged along a central
hallway. Each workstation in an Ethernet network can be viewed as an office
along this giant hallway. When one of these hypothetical offices needs to send
information to another, the worker in the office leans out into the corridor to see if
anyone else is sending a message, takes a deep breath, and yells the message,
which all the other offices receive. Thus, like sound in a corridor, the Ethernet
transmission travels to all the stations on the network. Every person in every
room hears the message and determines if it is for them.
Figure 3-1. The Ethernet Hallway
Because all the Ethernet stations on the network share this central corridor,
increases in traffic makes the availability of this corridor less and less likely. This
translates to a decrease in the available bandwidth as more stations are added to
the network. While a network may be able to move 9 Mbps with 10 stations on it,
the same network with 300 stations on it may only be able to move 2 or 3 Mbps.
Operation
Packets
The message that was shouted out into the corridor represents what is called a
packet. A packet is a collection of network data that a station transmits or
receives. It is a series of electrical impulses that represents binary information
(strings of “1”s and “0”s). The Ethernet packet, in the most elementary terms,
contains the following:
•
A destination address - Where the packet is headed to
•
A source address - Where the packet originated from
•
A data field - The content of the message
1001011001110110011101000111011001110101
1706n09
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