Telecom Dictionary

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OA&M 
operation administration & maintenance

OCC 
other common carriers

Ohms Restriction
Ohms Restriction is the same as Ohms resistance. Ohms are measures of resistance. A resistance 
of one Ohm allows one Ampere of current to pass at the electric potential of one Volt.

Open Systems Interconnection (OSI) standards
OSI standards are standards for the exchange of information among systems that are "open" to 
one another by virtue of incorporating ISO standards. The OSI reference model segments 
communications functions into seven layers. Each layer relies on the next lower layer to provide 
more primitive functions and, in turn, provides services to support the next higher layer.

Operating Telephone Company
An operating telephone company is any Bell-operating company or independent telephone 
company (termed exchange carrier in the MFJ) operating in North America.

Optical Fiber(s)
Optical fibers are light guides for electromagnetic waves in the infrared and visible light spectrum 
composed of concentric cylinders made of dielectric materials with different indices of refraction 
(i.e., velocity of propagation normalized to the velocity of light in free space). At the center is a 
core comprising the glass or plastic strand or fiber in which a light wave travels. A low index of 
refraction clad surrounds the core and is itself enclosed in a light-absorbing jacket that prevents 
interference among multi-fiber cables. Multi-fiber cable can be purchased with between 2 and 
136 fibers.

OPX 
off-premises extension

OSC 
operating system control

OSI 
open systems interconnection

OSS 
operations support systems or operational support system

Out Of Band Signaling
Out of band signaling uses the same channel path as the voice traffic but signaling is in a 
frequency band outside that used for the voice traffic. In digital systems, out-of-band signaling 
may take the appearance of an allocated bit position or a dedicated channel or time slot.