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). Symbol rate is half of data rate.
A competing encoding technique in the ISDN basic rate U interface, mainly used in Europe, is 4B3T.
Encoding
[edit]To minimize error propagation, bit pairs (dibits) are assigned to voltage levels according to a Gray 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 causes only a 1-bit error in the decoded data. 2B1Q code is not DC-balanced.
References
[edit]- ^ Reeve, Whitham D. (1995). Subscriber Loop Signaling and Transmission Handbook. IEEE Telecommunications Handbook Series. IEEE Press. ISBN 0780304403.
Line coding (digital baseband transmission) | ||
|---|---|---|
| Main articles |  | |
| Basic line codes | ||
| Extended line codes | ||
| Optical line codes | ||
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction