IDSL (ISDN Digital Subscriber Line)

A DSL variant that employs ISDN BRI (Basic Rate Inter-

face) technology to deliver symmetric transmission rates of 128 kbps or 144 kbps on unshielded twisted pair (UTP) local loops as long as 18,000 feet. IDSL bonds the two 64-kbps bearer (B) channels to provide a 128-kbps channel, and bonds the 16-kbps data (D) channel to bring the total to 144 kbps. Unlike ISDN, which is a circuit-switched network service for voice, data, fax, video, and multimedia, IDSL operates only at the local loop level to provide always-on Internet access. IDSL is virtually non-existent in the United States, where ISDN never enjoyed any significant success. As IDSL compares so unfavorably with asymmetric digital subscriber line (ADSL) and other DSL variants with respect to bandwidth, the very low IDSL penetration rates will only decrease. See also ADSL, always on, bandwidth, bonding, BRI, circuit switch, Internet, ISDN, local loop, symmetric, transmission rate, UTP, and xDSL.

• Table C-1: Twisted-Pair Categories of Performance
• Table D-1: Digital Hierarchy: T-Carrier, E-Carrier, and J-Carrier
• Table E-1: EBCDIC Code — 0–255 Decimal Notation
• Table E-2: EBCDIC Code — 00–FF Hexadecimal Notation
• Table E-3: European Digital Hierarchy: E-Carrier
• Table E-4: Frequency Spectrum: Band Designations, Nominal Frequency Ranges, Nominal
• Table E-4: Frequency Spectrum: Band Designations, Nominal Frequency Ranges, Nominal
• Table E-5: Endianess
• Table G-1: G-Series Recommendations
• Table H-1: H.320 Related Standards Recommendations
• 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