References on the whole "net" thing

[William Setzer IDM]

I'm looking for references that describe the physical layout of the "net".
What I'm looking for are answers to questions such as the following:

(1)  When the computer sends a packet to 192.48.96.2 (for example), what
     does each number mean, and what physically exists at each node?
     (Assuming of course each number between dots represents a "node".)

(2)  What is a "land bridge" and a "router", and what do they do?

(3)  What is internet (arpanet?) physically made up of?  Is it an underground
     dedicated line with some machinery (computers, "routers", etc) at some
     specified intervals?  Is there a map?

These are just questions representative of the material that I am seeking.
If anyone knows of any beginning to intermediate texts on the subject, could
you please mail them to the address in my .sig below?  Thanx a lot.

[Sorry if this isn't the right group for the post, but the 'protocol', 'lan',
 and 'news' type groups seemed inappropriate.]
--
William Setzer
setzer at epsl.umd.edu