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Two-binary, one-quaternary (2B1Q) is a line code used in the U interface of the Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) and the high-bit-rate digital subscriber line (HDSL). [1] 2B1Q is a four-level pulse-amplitude modulation (PAM-4) scheme without redundancy, mapping two bits (2B) into one quaternary symbol (1Q).
The first edition of ETR 152 specified the line code 2B1Q on either three pairs at 784 kbit/s each or two pairs at 1,168 kbit/s each. [3] A second edition of ETR 152, published in June 1995, specified trellis coded carrierless amplitude/phase modulation (CAP) as an alternative modulation scheme, running on two pairs at 1,168 kbit/s each. [4]
The gross bit rate is 160 kbit/s; 144 kbit/s throughput, 12 kbit/s sync and 4 kbit/s maintenance. The signals on the U reference point are encoded by two modulation techniques: 2B1Q in North America, Italy and Switzerland, and 4B3T elsewhere. Depending on the applicable cable length, two varieties are implemented, U pN and U p0.
2B1Q coding is defined in Appendix II of G.961, [9] ANSI T1.601, [7] and Annex A of ETR 080. [8] It can operate at distances up to about 18,000 feet ( 5.5 km ) with loss up to 42 dB . An internal termination impedance of 135 ohms is presented to the line at each end of the U-interface.
Early disk drives used very simple encoding schemes, such as RLL (0,1) FM code, followed by RLL (1,3) MFM code which were widely used in hard disk drives until the mid-1980s and are still used in digital optical discs such as CD, DVD, MD, Hi-MD and Blu-ray using EFM and EFMPLus codes. [11]
2B1Q—2 binary 1 quaternary; 2FA—Two-factor authentication; 2GL—second-generation programming language; 2NF—second normal form; 3GL—third-generation programming language; 3GPP—3rd Generation Partnership Project – 3G comms; 3GPP2—3rd Generation Partnership Project 2; 3NF—third normal form; 386—Intel 80386 processor; 486 ...
The RU is distinguished from a phone or line fault by the 8 mA it draws when powered from a 48 V source. 8 mA was chosen because a working phone never draws a continuous 8 mA under normal line conditions. Although DACS (1 + 2) uses the same 2B1Q signalling as basic rate ISDN, there are some significant differences:
The binary signal is encoded using rectangular pulse-amplitude modulation with polar NRZ(L), or polar non-return-to-zero-level code. In telecommunications, a non-return-to-zero (NRZ) line code is a binary code in which ones are represented by one significant condition, usually a positive voltage, while zeros are represented by some other significant condition, usually a negative voltage, with ...