DID (Direct Inward Dial)

A PBX feature that allows incoming calls to connect directly to the sta-

tion, without operator assistance. To accomplish this, each station is assigned a DID telephone number drawn from a bank of such numbers so designated by the local exchange carrier (LEC). (The last three or four digits of the DID number correspond to the internal station number, so the PBX dialing plan must be flexible enough to accommodate the DID numbering scheme.) When an outside caller dials that number, the terminating CO recognizes that fact and connects the call over a special DID trunk.The CO

passes the DID number to the PBX in advance of the call, thereby enabling the PBX to automatically route the call directly to the station, without the intervention of an attendant. The service provider rents DID numbers to user organizations in groups or blocks of 50, 100, or 250, typically.

• 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)
• Table V-2: Vertical Redundancy Check (VRC)
• Table V-3: Selected ITU-T V-Series Recommendations
• Table W-1: ITU-T Transmission Windows
• Table X-1: DSL Technology Comparisons
• Table X-2: ITU-T X Series Recommendation Groups
• Table X-3: Select X Series Recommendations
• TACS (Total Access Communications System)