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Glossary

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octet

Base-8 numbering system used to identify a section of a dotted dec-

imal IP address. Also referred to as a byte.

ones density

Also known as pulse density, this is a method of signal

clocking. The CSU/DSU retrieves the clocking information from data that
passes through it. For this scheme to work, the data needs to be encoded to
contain at least one binary 1 for each eight bits transmitted. See also: CSU
and DSU.

OSI

Open System Interconnection: International standardization program

designed by ISO and ITU-T for the development of data networking stan-
dards that make multivendor equipment interoperability a reality.

OSI reference model

Open System 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: Code 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.

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