Recall last lecture: the TCP
(transport layer) protocol is implemented in the two edge
systems involved in communications -- engineers say it's
implemented at the "edges" of the network.
TCP relies on the Internet Protocol (IP) to
deliver packets of data from one edge system to another. The
packets which IP delivers are usually called
datagrams.
Datagrams navigate zero or more (sometimes many)
routers, interconnecting the individual networks
which together make up the Internet. The word "Internet" is just a
contraction of the phrase "Interconnected Networks".
A router is essentially a special-purpose computer whose sole
function is to transfer datagrams between networks. In earlier
times, they were called "IP Gateways". The general structure of the
Internet can thus be visualised:
