Question

What is the collection of communication lines and routers called?

Answer 1

the collection of communication lines and routers are called as the subnet

I hope it hepls you

Answer 2

The collection of communication lines and routers are called "subnets".

Subnetwork is also known as the subnets, is a “logical subdivision” of IP address. The process of splitting a network into different networks is called subnetting. The IP addresses of computers under same subnet have an identical bit-group.

Subnets are an essential component in network which makes the communication possible.  

After subnetting, the IP address contains the identifier for Network, subnet and Host.