Question

why internet is called network of network

Answer 1

Internet is called network of networks because it connects computers all over the world forming a network.
And all computers are also connected to each other , hence computers form a network and when they all join with internet it is called network of networks.

Answer 2

The internet is a global network of computers. It is called a network of networks because rather than having one layer where all computers are connected together on the same level, computers are grouped together on separate networks or LANs (Local Area Network). These networks are small groups of computers which can all talk to each other. When any of these grouped computers needs to communicate with a computer outside of their group or "network" they will send information through what is called a "gateway" which will rout traffic across the internet to either another network or to a specific computer on the internet.ajit · 
  It initially linked more networks and never quit at doing that. :) Also, all computers connected to the internet are interconnected and accessible, so, theoretically, we're on the same giant network, using it's resources.
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