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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 device 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 group.
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 k
ey
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 The 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 The 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 Task Force. 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.