OAM (Operation and
Maintenance) Cell - A cell that is used to monitor virtual circuits.
OCA (Over Current Alarm)
- Available as a functional alarm from Marconi Communications battery and
converter power plants.
OCC (Other Common Carriers)
- Carriers providing long distance communications service other than
AT&T. These companies (including AT&T) are called IXCs
OC-n (Optical Carrier
level-n) - The optical counterpart of STS-n (the basic rate of 51.84
Mbps on which SONET is based is referred to as OC-1 or STS-1).
OC-48c (Concatenated OC-48) - 2.488 Gigabits per second carried as optical
OC-12c (Concatenated OC-12) - 622.08 Megabits per second carried as optical
OC-3c (Concatenated OC-3) - 155.52 Megabits per second carried as optical
Octet - A grouping
of 8 bits; similar, but not identical to, a byte.
OEM (Original Equipment
Manufacturer)- The maker of equipment that is marketed by another
vendor, usually under the name of the reseller. The OEM may
only manufacture certain components, or complete computers, which are then
often configured with software and/or other hardware by the reseller.
Office Alarm- Alarm
indicating a fault in a central office.
Office Records- A
permanent record developed to reflect the actual equipment and
arrangements in a central office.
Off-Line System- A
standby power system designed to provide power to equipment only when
commercial power fails (typically a full inverter system).
periods of time after the business day has ended during which carriers
offer discounted airtime charges.
Ohm- Measure of
resistance. A resistance of one Ohm allows one ampere to flow when a
potential difference of one volt is applied to the resistance.
Ohmmeter- Test set
which gives resistance readings in Ohms.
Ohm's Law- The law
which relates current measured as Amps (I), voltage (E) and resistance
measured as Ohms (R). The law is E = I x R. It can also be expressed as I
= E/R, or R = E/I.
OID (Object Identifier)
- The address of a MIB variable.
ONA (Open Network
Architecture) - A concept under which telephone companies are
obliged to provide a certain class of service to their own internal
value-added divisions and the same class of service to external,
nonaffiliated value-added companies.
One’s Density - The
requirement for digital transmission lines in the public switched telephone
network that eight consecutive "0"s cannot be in a digital data stream; exists
because repeaters and clocking devices within the network will lose timing
after receiving eight "0"s in a row; a number of techniques are used to insert
a "1" after every seventh-consecutive "0" (see Bit Stuffing).
On-Line Equipment -
Equipment which is in direct communication with a switching center or
On-Line System - A
standby power system designed to provide continuous power via the standby
power equipment to system equipment independent of the condition of the
commercial power (typically a -48VDC system).
OOF (Out-of-Frame) -
A signal condition and alarm in which some or all framing bits are lost.
Hewlett-Packard's network management software.
Optical Fiber Cable
- Cable made up of glass fibers protected by plastic coverings; sometimes
metallic wires are included as strength members.
Oscilloscope - A
device that produces a visual trace of a voltage or current wave shape,
generally on a cathode ray tube.
OSI (Open Systems
Interconnection) - The 7-layer suite of protocols designed by ISO
committees to be the international standard computer network
OSP (Outside Plant)
- The outside plant includes all cables and wires extending outward from
the network protectors on the main distribution frame,
supporting structures, and other associated apparatus necessary to connect
the terminal equipment to the outside plant.
OSPF (Open Shortest Path
First) Protocol - A routing algorithm for IP that incorporates
least-cost, equal-cost, and load balancing.
OUI (Organizationally Unique
Identifier) - Part of RFC 1483. A three-octet field in the SubNetwork
Attachment Point (SNAP) header, identifying an organization which administers
the meaning of the following two octet Protocol Identifier (PID) field in the
SNAP header. Together they identify a distinct routed or bridged protocol.
- Refers to switch configuration via the serial port or over Ethernet, not
Out Of Phase -
Waves of the same frequency, but different time relation, that do not pass
through their zero and maximum points at the same instant.
Output - (1) Data
that flows out of a computer to any device; (2) in
specification description language, an action within a transition which
generates a signal which, in turn, acts as an input elsewhere; and (3)
power, current or voltage at the output of a device.
Output Rating - (1)
The power available at the output terminals of a transmitter or power
supply when connected to the normal load or its equivalent; and (2) under
specified ambient conditions, the power that can be delivered by a
device over a long period of time without overheating.
Output Transformer -
Transformer which matches power output of an amplifier to impedance of a
Outside Link - A
link to a lowest level outside node.
Outside Node - A
node which is participating in PNNI routing, but which is not a member of a
particular peer group.
Overbooking - A VBR
process used to increases total link capacity by a factor.
- Protection of power supplies, conductors, and connected equipment from
excessive flow of input or output current, including the short circuited
Overload - (1) A
load greater than that for which the power source has been designed; and
(2) on a transmission system, a higher level than that for which the
system was designed. Overload produces distortion.
- A circuit breaker or mechanical fuse which opens when the current is
greater than that which the equipment has been designed to carry.
Overload Rating -
Some load in excess of the nominal rating, which a device can carry for a
specified length of time without being damaged.
- Protection of the power supply or parts of it against temperatures
exceeding specified values.
- Protection of the power supply and/or connected equipment against output
voltage, including the open circuit voltage.
Overvoltage Relay -
Alarm relay which operates when voltage across it exceeds a preset level.