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Appendix A - TCP/IP Description
UDP, described in RFC 768 (http://info.internet.isi.edu:80/in-notes/rfc/files/rfc768.txt) provides an
end-to-end datagram (connectionless) service. Some applications, such as those that involve a
simple query and response, are better suited to the datagram service of UDP because there is no
time lost to virtual circuit establishment and termination. UDP’s primary function is to add a port
number to the IP address to provide a socket for the application.
The Application Layer protocols are examples of common TCP/IP applications and utilities, which
include:
• Telnet (Telecommunication Network): a virtual terminal protocol allowing a user logged on to
one TCP/IP host to access other hosts on the network, described in RFC 854 (http://
info.internet.isi.edu:80/in-notes/rfc/files/rfc854.txt).
• FTP: the File Transfer Protocol allows a user to transfer files between local and remote host
computers per RFC 959 (http://info.internet.isi.edu:80/in-notes/rfc/files/rfc959.txt).
• Archie: a utility that allows a user to search all registered anonymous FTP sites for files on a
specified topic.
• Gopher: a tool that allows users to search through data repositories using a menu-driven,
hierarchical interface, with links to other sites, per RFC 1436 (http://info.internet.isi.edu:80/in-
notes/rfc/files/rfc1436.txt).
• SMTP: the Simple Mail Transfer Protocol is the standard protocol for the exchange of
electronic mail over the Internet, per RFC 821 (http://info.internet.isi.edu:80/in-notes/rfc/files/
rfc821.txt).
• HTTP: the Hypertext Transfer Protocol is the basis for exchange of information over the
World Wide Web (WWW). Various versions of HTTP are in use over the Internet, with HTTP
version 1.0, per RFC 1945 (http://info.internet.isi.edu:80/in-notes/rfc/files/rfc1945.txt) being
the most current.
• HTML: WWW pages are written in the Hypertext Markup Language (HTML), an ASCII-based,
platform-independent formatting language, per RFC 1866 (http://info.internet.isi.edu:80/in-
notes/rfc/files/rfc1866.txt).
• Finger: used to determine the status of other hosts and/or users, per RFC 1288 (http://
info.internet.isi.edu:80/in-notes/rfc/files/rfc1288.txt).
• POP: the Post Office Protocol defines a simple interface between a user’s mail reader
software and an electronic mail server; the current version is POP3, described in RFC 1460
(http://info.internet.isi.edu:80/in-notes/rfc/files/rfc1460.txt).
• DNS: the Domain Name System defines the structure of Internet names and their association
with IP addresses, as well as the association of mail, name, and other servers with domains.
• SNMP: the Simple Network Management Protocol defines procedures and management
information databases for managing TCP/IP-based network devices. SNMP, defined by RFC
1157 (http://info.internet.isi.edu:80/in-notes/rfc/files/rfc1157.txt) is widely deployed in local and
wide area network. SNMP Version 2 (SNMPv2), per RFC 1441 (http://info.internet.isi.edu:80/
in-notes/rfc/files/rfc1441.txt) adds security mechanisms that are missing in SNMP, but is also
more complex.
• Ping: a utility that allows a user at one system to determine the status of other hosts and the
latency in getting a message to that host. Ping uses ICMP Echo messages.
• Whois/NICNAME: Utilities that search databases for information about Internet domain and
domain contact information, per RFC 954 (http://info.internet.isi.edu:80/in-notes/rfc/files/
rfc954.txt).
• Traceroute: a tool that displays the route that packets will take when traveling to a remote
host.