OPX (Off-Premises eXtension)

Synonymous with off-premises station (OPS). A key telephone sys-

tem (KTS) or PBX station or extension that terminates on a telephone physically located off-premises, typically on a non-contiguous property. In addition to a special line card, an OPX requires a dedicated private line, typically leased from the local exchange carrier (LEC).The OPX enjoys all of the features of an extension located on-premises, but at considerable cost. OPXs are, and always were, uncommon, but sometimes are used to connect a distant guard shack or security building to the PBX or perhaps to provide a technically challenged key executive with a PBX extension at home. See also KTS, LEC, and PBX.

• Table H-2: SDTV Scanning Formats
• Table H-3: Notation Comparison
• Table H-4: Selected ITU-T H-Series Recommendations
• Table I-1: Frame Relay Implementation Agreements
• Table I-2: Index of Refraction (IOR)
• Table I-3: IPv4 Address Classes
• Table I-4: Selected ITU-T I-Series Recommendations
• Table I-4: Selected ITU-T I-Series Recommendations (continued)
• Table I-5: ITU-T Series Recommendations
• Table J-1: Japanese Digital Hierarchy: J-carrier
• Table L-1: Longitudinal Redundancy Check (LRC)
• Table M-1: International Morse Code
• Table O-1: OSI Reference Model Layers
• Table O-2: G.709 Line Rates and Corresponding SDH/SONET Line Rates
• Table P-1: Evolution of PBX technology
• Table P-2: Military and Aviation Phonetic Alphabet
• Table Q-1: Selected ITU-T Q-Series Recommendations
• Table R-1: Before and After: Bell Operating Companies (BOCs) and Regional Bell Operating
• Table R-1: Before and After: Bell Operating Companies (BOCs) and Regional Bell Operating
• Table R-2: Coaxial Cable Types
• Table S-1: SDTV Scanning Formats
• Table S-2: SONET/SDH Signal Hierarchy
• Table T-1: North American Digital Hierarchy: T-carrier
• Table T-2: TCP/IP Protocol Suite
• Table V-1: Electromagnetic Signal Propagation Velocity (Approximate)