IP is built on several principles:
for each packet sent, a routing decision is taken -- no circuits
it is the application at each end of the "circuit" that are in control (also called "edge", as opposed to "middle"), and not the equipments along the way
"IP is robust, but not reliable" -- it makes no garantee that the packet will reach destination -- it is the responbility of higher level protocols/applications
IP will run over any media -- copper, fiber, radio, smoke signals, etc... It is said of IP that it is at the center of an "hourglass" model:
+------+------+-----+-----+ | SMTP | HTTP | DNS | NTP | \------+------+-----+----/ \ TCP | UDP / \-----------+--------/ | IP | /-----+-------+------\ / TR | ETHER | PtP \ /-------+-------+--------\ | UTP/STP/COAX |Hz/MODEM| +---------------+--------+
Unlike the OSI model, IP has only 4 layers (Physical/Link, Network, Transport, Application).