MMS43 code
4b3t ( M odified M onitored S to 43 - Code ) is a line code from the field of telecommunications . Three ternary (three-valued) values with the steps , and are formed from four binary values (bits) . It is therefore also called the 4B3T code (4 binary 3 ternary).
-0+
The coding achieves freedom from DC signals in the power density spectrum of the transmission signal. This is particularly necessary so that the signal can pass through the usual transmitters in the telephone network . However, the coding adds a relative redundancy of 0.159 to the signal .
The 4B3T coding is mainly for the U K0 - subscriber line at ISDN - bases used.
DC component suppression
In order to achieve freedom from DC signals, the transmitter / encoder tracks the DC component that has accumulated up to now and uses different output words for some of the 16 possible input words so that the total accumulated DC component remains limited.
The following output words are free of equal parts and do not change the accumulated equal part:
| 3T | 4B |
|---|---|
| 0 0 0 | Line not used |
| + 0 - | 1011 |
| + - 0 | 0010 |
| 0 + - | 1110 |
| 0 - + | 0001 |
| - 0 + | 0111 |
| - + 0 | 0100 |
The following output words have a constant component, therefore two output words are assigned to each input word (a "positive" and a "negative"):
| 3T (pos) | 3T (neg) | 4B |
|---|---|---|
| + 0 + | 0 - 0 | 0000 |
| 0 0 + | - - 0 | 0011 |
| 0 + + | - 0 0 | 0101 |
| - + + | - - + | 0110 |
| + 0 0 | 0 - - | 1000 |
| + - + | - - - | 1001 |
| + + - | + - - | 1010 |
| + + + | - + - | 1100 |
| 0 + 0 | - 0 - | 1101 |
| + + 0 | 0 0 - | 1111 |