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Glossary
OSI reference model
Open Systems Interconnection reference model: A
conceptual model defined by the International Organization for Standard-
ization (ISO), describing how any combination of devices can be connected
for the purpose of communication. The OSI model divides the task into
seven functional layers, forming a hierarchy with the applications at the top
and the physical medium at the bottom, and it defines the functions each
layer must provide. See also: application layer, data link layer, network
layer, physical layer, presentation layer, session layer,
and transport layer.
OSPF
Open Shortest Path First: A link-state, hierarchical IGP routing algo-
rithm derived from an earlier version of the IS-IS protocol, whose features
include multipath routing, load balancing, and least-cost routing. OSPF is
the suggested successor to RIP in the Internet environment. See also:
Enhanced IGRP, IGP,
and IP.
OUI
Organizationally Unique Identifier: Is assigned by the IEEE to an
organization that makes network interface cards. The organization then puts
this OUI on each and every card they manufacture. The OUI is 3 bytes (24
bits) long. The manufacturer then adds a 3-byte identifier to uniquely iden-
tify the host on an internetwork. The total length of the address is 48 bits (6
bytes) and is called a hardware address or MAC address.
out-of-band management
Management "outside" of the network's
physical channels. For example, using a console connection not directly
interfaced through the local LAN or WAN or a dial-in modem. Compare to:
in-band management.
out-of-band signaling
Within a network, any transmission that uses
physical channels or frequencies separate from those ordinarily used for data
transfer. For example, the initial configuration of a Cisco Catalyst switch
requires an out-of-band connection via a console port.
packet
In data communications, the basic logical unit of information
transferred. A packet consists of a certain number of data bytes, wrapped or
encapsulated in headers and/or trailers that contain information about
where the packet came from, where it's going, and so on. The various pro-
tocols involved in sending a transmission add their own layers of header
information, which the corresponding protocols in receiving devices then
interpret.
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