Apple Mac OS X Server (Administrator’s Guide) - Manual (Page 589)

Glossary 589
T
TCP (Transmission Control Protocol) A method used along with the Internet Protocol
(IP) to send data in the form of message units between computers over the Internet. IP takes
care of handling the actual delivery of the data, and TCP takes care of keeping track of the
individual units of data (called packets) into which a message is divided for efficient routing
through the Internet.
Tomcat The official reference implementation for Java Servlet 2.2 and JavaServer Pages 1.1,
two complementary technologies developed under the Java Community Process.
TTL (time-to-live) The specified length of time that DNS information is stored in a cache.
When a domain name–IP address pair has been cached longer than the TTL value, the entry
is deleted from the name server’s cache (but not from the primary DNS server).
U
UDP (User Datagram Protocol) A communications method that uses the Internet
Protocol (IP) to send a data unit (called a datagram) from one computer to another in a
network. Network applications that have very small data units to exchange may use UDP
rather than TCP.
UID (user ID) A number that uniquely identifies a user. Mac OS X computers use the UID
to keep track of a user’s directory and file ownership.
Unicode A standard that assigns a unique number to every character, regardless of
language or the operating system used to display the language.
URL (Uniform Resource Locator)
The address of a computer, file, or resource that can
be accessed on a local network or the Internet. The URL is made up of the name of the
protocol needed to access the resource, a domain name that identifies a specific computer
on the Internet, and a hierarchical description of a file location on the computer.
USB (Universal Serial Bus) A standard for communicating between a computer and
external peripherals using an inexpensive direct-connect cable.
user name
The long name for a user, sometimes referred to as the user’s “real” name. See
also short name.
V
virtual user An alternate email address (short name) for a user.
VPN (Virtual Private Network) A network that uses encryption and other technologies to
provide secure communications over a public network, typically the Internet. VPNs are generally
cheaper than real private networks using private lines but rely on having the same encryption
system at both ends. The encryption may be performed by firewall software or by routers.