Principal causes of mistakes at data transfer can be a lot:

• Damages of cable system
• Defects of the active equipment
• Congestion of resources
• Mistakes of the software

Frequently one defects mask others. That is why effective diagnostics needs complex diagnostics. It includes some stages:

• Revealing of physical defects
• Measurement of congestion of a communications channel
• Measurement of number of collisions, definition of their reasons
• Measurements of quantity of mistakes of data transfer at a level of a communications channel. As it influences for the period of reaction of the software
• Revealing defects in architecture
• Revealing defects the software