802.3 CSMA/CD Hardware Requirements
An example of Standard Ethernet' or 10BASE-5 is given in the figure below:
10BASE-5 Hardware Components
The format of a transmitted 802.3 frame is shown in Figure 1.
Figure 1. Format of a Typical CSMA/CD Frame
Preamble Field - This allows the receiving electronics of the MAC unit to achieve synchronisation with the frame.
Start of Frame a Delimiter (SFD) - This contains the pattern 10101011 and indicates the start of valid frame.
Destination and Source Address - Each address may be either 16 or 48 bits. This size must naturally be consistent for all nodes in a particular LAN installation.
Length Indicator - This is a two byte field which indicates the number of bytes in the data field.
Frame Check Field - This contains a 32 bit cyclic redundancy check that is used for error detection.