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.