gawkinet: Basic Protocols
1.3.1 The Basic Internet Protocols
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IP
The Internet Protocol. This protocol is almost never used directly
by applications. It provides the basic packet delivery and routing
infrastructure of the Internet. Much like the phone company's
switching centers or the Post Office's trucks, it is not of much
day-to-day interest to the regular user (or programmer). It
happens to be a best effort datagram protocol. In the early
twenty-first century, there are two versions of this protocol in
use:
IPv4
The original version of the Internet Protocol, with 32-bit
addresses, on which most of the current Internet is based.
IPv6
The "next generation" of the Internet Protocol, with 128-bit
addresses. This protocol is in wide use in certain parts of
the world, but has not yet replaced IPv4.(1)
Versions of the other protocols that sit "atop" IP exist for both
IPv4 and IPv6. However, as the IPv6 versions are fundamentally the
same as the original IPv4 versions, we will not distinguish further
between them.
UDP
The User Datagram Protocol. This is a best effort datagram
protocol. It provides a small amount of extra reliability over IP,
and adds the notion of "ports", described in 
TCP and UDP
Ports Ports.
TCP
The Transmission Control Protocol. This is a duplex, reliable,
sequenced byte-stream protocol, again layered on top of IP, and
also providing the notion of ports. This is the protocol that you
will most likely use when using 'gawk' for network programming.
All other user-level protocols use either TCP or UDP to do their
basic communications. Examples are SMTP (Simple Mail Transfer
Protocol), FTP (File Transfer Protocol), and HTTP (HyperText Transfer
Protocol).
---------- Footnotes ----------
(1) There isn't an IPv5.
Info Catalog
gawkinet: The TCP/IP Protocols
gawkinet: The TCP/IP Protocols
gawkinet: Ports