World is emerging in a large network. Most real computer users should know how to deal with small and medium networks. Most computer users know almost nothing about networks because they don't see a reason why they need to learn about something which is not used directly in the production process. Actually the company network is one of the most important parts of the business, medium companies can lose more than $40k in an hour of network downtime. Generally most company networks are small or medium networks, large networks being used by national data service providers.