4B3T: Difference between revisions
m Robot: Changing template: com-stub |
Added encoding and decoding tables. |
||
| Line 1: | Line 1: | ||
'''4B3T''' stands for 4 (four) [[Binary numeral system|Binary]] 3 (three) [[Ternary signal|Ternary]], a [[line encoding]] scheme used for [[ISDN]] BRI interface. 4B3T represents four binary bits using three pulses. It uses three states viz. + (positive pulse), no pulse |
'''4B3T''' stands for 4 (four) [[Binary numeral system|Binary]] 3 (three) [[Ternary signal|Ternary]], a [[line encoding]] scheme used for [[ISDN]] BRI interface. 4B3T represents four binary bits using three pulses. It uses three states viz. + (positive pulse), 0 (no pulse), and − (negative pulse). This means we have 16 (2<sup>4</sup>) input combinations to represent, using 27 output combinations. 000 is not used to avoid long periods without a transition. To avoid DC buildup on the physical medium inputs are either mapped to a single combination with no net DC (one + and one −) or to a pair of combinations with differing net DC (e.g. ++− and −−+). When transmitting the DC buildup is tracked and a combination chosen that has a DC component of the opposite sign to the running total. |
||
This mapping from 4 bits to 3 ternary states is given in a table known as Modified Monitoring State 43 (MMS43). |
This mapping from 4 bits to 3 ternary states is given in a table known as Modified Monitoring State 43 (MMS43). |
||
A competing encoding technique, used for the ISDN [[basic rate interface]] where 4B3T is not used, is [[2B1Q]]. |
A competing encoding technique, used for the ISDN [[basic rate interface]] where 4B3T is not used, is [[2B1Q]]. |
||
==Encoding table== |
|||
<!-- Source: http://www.infineon.com/cms/en/product/channel.html?channel=ff80808112ab681d0112ab69a79202a5 --> |
|||
Encoding uses a 4-state machine, which tracks the accumulated disparity, the number of + pulses minus the number of – pulses. The starting value is arbitrary; here we use the values 1 through 4, although –1.5, -0.5, +0.5 and +1.5 is another possibility. |
|||
{|class=wikitable style="text-align:center" |
|||
|+MMS 43 coding table |
|||
!rowspan=2| Input !!colspan=4| Accumulated Disparity |
|||
|- |
|||
!width=20%| 1 !!width=20%| 2 !!width=20%| 3 !!width=20%| 4 |
|||
|- |
|||
! 0000 |
|||
| + 0 + (+2) ||colspan=3| 0 – 0 (–1) |
|||
|- |
|||
! 0001 |
|||
|colspan=4| 0 – + (+0) |
|||
|- |
|||
! 0010 |
|||
|colspan=4| + – 0 (+0) |
|||
|- |
|||
! 0011 |
|||
|colspan=3| 0 0 + (+1) || – – 0 (–2) |
|||
|- |
|||
! 0100 |
|||
|colspan=4| – + 0 (+0) |
|||
|- |
|||
! 0101 |
|||
| 0 + + (+2) ||colspan=3| – 0 0 (–1) |
|||
|- |
|||
! 0110 |
|||
|colspan=2| – + + (+1) ||colspan=2| – – + (–1) |
|||
|- |
|||
! 0111 |
|||
|colspan=4| – 0 + (+0) |
|||
|- |
|||
! 1000 |
|||
|colspan=3| + 0 0 (+1) || 0 – – (–2) |
|||
|- |
|||
! 1001 |
|||
|colspan=3| + – + (+1) || – – – (–3) |
|||
|- |
|||
! 1010 |
|||
|colspan=2| + + – (+1) ||colspan=2| + – – (–1) |
|||
|- |
|||
! 1011 |
|||
|colspan=4| + 0 – (+0) |
|||
|- |
|||
! 1100 |
|||
| + + + (+3) ||colspan=3| – + – (–1) |
|||
|- |
|||
! 1101 |
|||
|colspan=3| 0 + 0 (+1) || – 0 – (–2) |
|||
|- |
|||
! 1110 |
|||
|colspan=4| 0 + – (+0) |
|||
|- |
|||
! 1111 |
|||
| + + 0 (+2) ||colspan=3| 0 0 – (–1) |
|||
|} |
|||
== Decoding table == |
|||
Decoding is simpler, as the decoder does not need to keep track of the encoder state. The 000 triplet is not a legal encoded sequence, but is typically decoded as binary 0000. |
|||
{|class=wikitable style="text-align:center" |
|||
!colspan=2| Ternary !! Binary |
|||
|- |
|||
| + 0 + || 0 – 0 || 0000 |
|||
|- |
|||
| 0 – + || || 0001 |
|||
|- |
|||
| + – 0 || || 0010 |
|||
|- |
|||
| 0 0 + || – – 0 || 0011 |
|||
|- |
|||
| – + 0 || || 0100 |
|||
|- |
|||
| 0 + + || – 0 0 || 0101 |
|||
|- |
|||
| – + + || – – + || 0110 |
|||
|- |
|||
| – 0 + || || 0111 |
|||
|- |
|||
| + 0 0 || 0 – – || 1000 |
|||
|- |
|||
| + – + || – – – || 1001 |
|||
|- |
|||
| + + – || + – – || 1010 |
|||
|- |
|||
| + 0 – || || 1011 |
|||
|- |
|||
| + + + || – + – || 1100 |
|||
|- |
|||
| 0 + 0 || – 0 – || 1101 |
|||
|- |
|||
| 0 + – || || 1110 |
|||
|- |
|||
| + + 0 || 0 0 – || 1111 |
|||
|} |
|||
==See also== |
==See also== |
||
Revision as of 11:02, 24 October 2008
4B3T stands for 4 (four) Binary 3 (three) Ternary, a line encoding scheme used for ISDN BRI interface. 4B3T represents four binary bits using three pulses. It uses three states viz. + (positive pulse), 0 (no pulse), and − (negative pulse). This means we have 16 (24) input combinations to represent, using 27 output combinations. 000 is not used to avoid long periods without a transition. To avoid DC buildup on the physical medium inputs are either mapped to a single combination with no net DC (one + and one −) or to a pair of combinations with differing net DC (e.g. ++− and −−+). When transmitting the DC buildup is tracked and a combination chosen that has a DC component of the opposite sign to the running total.
This mapping from 4 bits to 3 ternary states is given in a table known as Modified Monitoring State 43 (MMS43). A competing encoding technique, used for the ISDN basic rate interface where 4B3T is not used, is 2B1Q.
Encoding table
Encoding uses a 4-state machine, which tracks the accumulated disparity, the number of + pulses minus the number of – pulses. The starting value is arbitrary; here we use the values 1 through 4, although –1.5, -0.5, +0.5 and +1.5 is another possibility.
| Input | Accumulated Disparity | |||
|---|---|---|---|---|
| 1 | 2 | 3 | 4 | |
| 0000 | + 0 + (+2) | 0 – 0 (–1) | ||
| 0001 | 0 – + (+0) | |||
| 0010 | + – 0 (+0) | |||
| 0011 | 0 0 + (+1) | – – 0 (–2) | ||
| 0100 | – + 0 (+0) | |||
| 0101 | 0 + + (+2) | – 0 0 (–1) | ||
| 0110 | – + + (+1) | – – + (–1) | ||
| 0111 | – 0 + (+0) | |||
| 1000 | + 0 0 (+1) | 0 – – (–2) | ||
| 1001 | + – + (+1) | – – – (–3) | ||
| 1010 | + + – (+1) | + – – (–1) | ||
| 1011 | + 0 – (+0) | |||
| 1100 | + + + (+3) | – + – (–1) | ||
| 1101 | 0 + 0 (+1) | – 0 – (–2) | ||
| 1110 | 0 + – (+0) | |||
| 1111 | + + 0 (+2) | 0 0 – (–1) | ||
Decoding table
Decoding is simpler, as the decoder does not need to keep track of the encoder state. The 000 triplet is not a legal encoded sequence, but is typically decoded as binary 0000.
| Ternary | Binary | |
|---|---|---|
| + 0 + | 0 – 0 | 0000 |
| 0 – + | 0001 | |
| + – 0 | 0010 | |
| 0 0 + | – – 0 | 0011 |
| – + 0 | 0100 | |
| 0 + + | – 0 0 | 0101 |
| – + + | – – + | 0110 |
| – 0 + | 0111 | |
| + 0 0 | 0 – – | 1000 |
| + – + | – – – | 1001 |
| + + – | + – – | 1010 |
| + 0 – | 1011 | |
| + + + | – + – | 1100 |
| 0 + 0 | – 0 – | 1101 |
| 0 + – | 1110 | |
| + + 0 | 0 0 – | 1111 |
See also
Other line codes that have 3 states:
 | This article related to telecommunications is a stub. You can help Wikipedia by expanding it. |