Specifications

4-1
Chapter 4
Ethernet Data Frames
Most computer networks require that information transmitted between two stations be divided into
blocks called frames. For these frames to be sent successfully to other devices on the network, certain
protocol and routing information must be added to the data. In addition, the way this information is
arranged inside the frame must conform to a specific format. The way an Ethernet device places the
data bits into frames before it is placed on the LAN is called Manchester Encoding.
The following chapter discusses Manchester Encoding and describes the four different Ethernet frame
types.
Manchester Encoding
The information that is to be transmitted on the cable is in the form of a
constantly changing voltage signal. This signal is electronically
transformed into a D. C. signal with a value of either 0 volts or -1.2 volts.
The value of the D. C. signal is found by periodically sampling the voltage
value of the original signal and assigning it one of the two values,
depending on the value found at the time it was checked. The result is to
change a non-constant analog signal into a digital signal with a value
toggling between either 0 or -1.2 volts.