2B1Q

Two- binary, one- quaternary (2B1Q) is a physical layer encoding used for Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) implementations. 2B1Q uses four signal levels, which are −450 mV, −150 mV, 150 mV and 450 mV, each (1Q) equivalent to two bits (2b). A competing encoding technique, also used for ISDN basic rate interfaces, is 4B3T.

To minimize error propagation, bit pairs (dibits) are assigned to voltage levels according to a Gray code, as follows:

If the voltage is misread as an adjacent level, this will only cause a 1-bit error in the decoded data. 2B1Q is also used for some variants of HDSL. 2B1Q code is not DC-balanced. Symbol rate is half of data rate.

v t e Line coding (digital baseband transmission) Main articles Unipolar encoding · Bipolar encoding · On-off keying Basic line codes Return to zero (RZ) · Non-return-to-zero, level (NRZ/NRZ-L) · Non-return-to-zero, inverted (NRZ-I) · Non-Return-to-Zero, space (NRZ-S) · Manchester · Differential Manchester/Biphase (Bi-φ) Extended line codes Conditioned Diphase · 4B3T · 4B5B · 2B1Q · Alternate Mark Inversion · Modified AMI code · Coded mark inversion · MLT-3 encoding · Hybrid ternary code · 6b/8b encoding · 8b/10b encoding · 64b/66b encoding · Eight-to-fourteen modulation · Delay/Miller encoding · TC-PAM Optical line codes Carrier-Suppressed Return-to-Zero · Alternate-Phase Return-to-Zero See also: Baseband · Baud · Bit rate · Digital signal · Digital transmission · Ethernet physical layer · Pulse modulation methods · Pulse-amplitude modulation (PAM) · Pulse code modulation (PCM) · Serial communication · Category:Line codes

This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

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