440 GLOSSARY
header The control information added to the beginning of a transmitted
message. This may consist of packet or block address, destination,
message number and routing instructions.
hierarchical network A network with one host at its hub, which is the major processing center,
and one or more satellite processing units.
hot swap The ability of a de vice to have parts removed and replaced without
turning off the device and without interrupting the service the device
provides.
hub The center of a star topology network or cabling system. A multi-node
network topology that has a central multiplexer with many nodes feeding
into and through the multiplexer or hub. The nodes do not directly
interconnect.
hunt groups Informal “call centers” in which a call rings to one member of the g roup.
If there is not answer, the call rings at the next member’s telephone and
so on until a member answers.
hybrid mode A PBX operating mode in which some outside lines are grouped together
in pools while other lines are assigned directly to buttons on telephones.
Users access outside lines by dialing a pool access code. See also key
mode.
IEEE Institute of Electrical and Electronic Engineers. A U.S. publishing and
standards organization responsible for many LAN standards, such as the
802 series.
IEEE 802.2 Th e Data Link standard for use with IEEE 802.3, 802.4 and 802.5
standards. It specifies how a basic data connection should be set up over
the cable.
IEEE 802.3 Th e Ethernet standard. A physical layer definition that includes
specification for cabling plus the method of transmitting data and
controlling access to the cable.
IETF Internet Engineering TaskForce. The standards-setting body for the
Internet. Protocols adopted by the IETF define the structure and the
operation of the Internet.
IMAP Internet Message Access Protocol. A method of accessing electronic
messages that are kept on a server. IMAP defines how an e-mail program
can access messages that are stored on a remote server.