2B1Q
Encyclopedia
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.
Physical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
encoding
Encoder
An encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.-Media:...
used for Integrated Services Digital Network
Integrated Services Digital Network
Integrated Services Digital Network is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network...
(ISDN) Basic Rate Interface
Basic rate interface
Basic Rate Interface is an Integrated Services Digital Network configuration intended primarily for use in subscriber lines similar to those that have long been used for plain old telephone service...
(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
4B3T
4B3T stands for 4 Binary 3 Ternary, a line encoding scheme used for ISDN BRI interface. 4B3T represents four binary bits using three pulses.It uses three states:* + ,* 0 , and* − ....
.
To minimize error propagation, bit pairs (dibits) are assigned to voltage levels according to a Gray code
Gray code
The reflected binary code, also known as Gray code after Frank Gray, is a binary numeral system where two successive values differ in only one bit. It is a non-weighted code....
, as follows:
| Dibit | Signal level |
|---|---|
| 10 | +450 mV |
| 11 | +150 mV |
| 01 | −150 mV |
| 00 | −450 mV |
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.