O

OC

Optical Carrier: A series of physical protocols, designated as OC-1, OC-2, OC-3, and so on, for SONET optical signal transmissions. OC signal levels place STS frames on a multimode fiber-optic line at various speeds, of which 51.84Mbps is the lowest (OC-1). Each subsequent protocol runs at a speed divisible by 51.84. See also: SONET.

offline operation

During offline operation, the host or computer is not connected to the Internet or even possibly to the LAN.

100BaseT

Based on the IEEE 802.3 standard, 100BaseT is the Fast Ethernet specification of 100Mbps baseband that uses UTP wiring. 100BaseT sends link pulses (containing more information than those used in 10BaseT) over the network when no traffic is present. See also: 10BaseT, Fast Ethernet, and IEEE 802.3.

100BaseTX

Based on the IEEE 802.3 standard, 100BaseTX is the 100Mbps baseband Fast Ethernet specification that uses two pairs of UTP or STP wiring. The first pair of wires receives data; the second pair sends data. To ensure correct signal timing, a 100BaseTX segment cannot be longer than 100 meters.

optimum switching

One of the NetFlow switching types, optimum switching remains the most efficient switching mode and results in the highest throughput when extensive access list processing is not required.

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 standards that make multivendor equipment interoperability a reality.

OSI reference model

Open System Interconnection reference model: A conceptual model defined by the International Standardization Organization (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, Session layer, Data Link layer, Network layer, Physical layer, Presentation layer, and Transport layer.

OSPF

Open Shortest Path First: A link-state, hierarchical IGP routing algorithm 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.

out-of-band management (OOBM)

Management “outside” of the network’s physical channels using a console connection.

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.