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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).
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.
Through the use of 2B1Q encoding, two bits are combined to one symbol, further reducing the symbol rate by a factor of two. For this two-pair 2B1Q variant of HDSL, framing increases the bitrate from 1.544 Mbit/s to 1.568 Mbit/s, resulting in a symbol rate of 392 kilobaud and a Nyquist frequency of 196 kHz.
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.
It is like ISDN in that it uses a single-wire pair to transmit full-duplex data at 128 kbit/s and at distances of up to RRD range [definition needed]. Like ISDN, IDSL uses a 2B1Q line code to enable transparent operation through the ISDN U interface.
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 ...
Signal Comments 1 state 0 state NRZ–L: Non-return-to-zero level. This is the standard positive logic signal format used in digital circuits. forces a high level
The copper pair between the EU and RU, which carries the 2B1Q signalling and the 140 V DC for powering the RU and subscribers' telephones. The 140 V DC is not applied to the line until an RU is detected so that engineers do not get a shock. It is also removed as soon as the RU is disconnected, again for safety.