Installation PTN-2-C37.94 with E1/PTN-2-C37.94 with T1
13
Release 01 02/2018
Figure 8
C37.94 Framing
2.2.5
AMI, HDB3 and B8ZS Coding
AMI, HDB3 and B8ZS are different types of line coding. HDB3 is used in E1 whereas B8ZS is
used in T1 communications systems. The 2-C37.94 module supports HDB3 for E1 and B8ZS
for T1. HDB3 and B8ZS is an enhancement of AMI. For this reason, AMI is mentioned here as
well.
NOTE:
C37.94 is pure optical. As a result, line coding for C37.94 is not relevant;
As the E1/T1 link has no separate clock transmission, the receiver will derive the clock from
the incoming data stream. A minimum density of logical ones is required in order to
guarantee a faultless clock recovery. This is achieved basically by AMI which encodes the
data stream with bipolar violations. A more enhanced and better encoding is HDB3 and B8ZS
which enhance the AMI stream by replacing successive zeros:
E1
HDB3: replace four successive zeros with a fixed bit pattern ‘000V’ or ‘B00V’;
T1
B8ZS: replace eight successive zeros with a fixed bit pattern ‘000VB0VB’;
A ‘B’ and ‘V’ can either be ‘-‘ or ‘+’. Which pattern is used depends on the amount of ‘+’ and
‘-‘ already received. The choice is such that the number of pluses (+) between two successive
violations (V) is odd.
Figure 9
HDB3 Encoding
Figure 10
T1: B8ZS Encoding
125 µs (=32*8 = 256 bits)
N = 4 Data Channels
12 – N = 8
filled with ‘1’
1 C37.94 Frame = 256 bits = 125
µs
H = Header
= 16 bits = Synchronisation
(=2 E1 timeslots)
OH = Overhead = 48 bits = Includes N (=6 E1 timeslots)
T = All Timeslots = 192 bits = 12*8*2 = Channel Data (=2 E1 timeslots per C37.94 data channel)
D = Channel Data = N*8*2
T0 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T20 T21 T22 T23 T24 T25 T26 T27 T28 T29 T30 T31
8 bits
H
OH
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
H
OH
D1D1 D2D2 D3D3 D4D4
‘1’
‘1’
‘1’
‘1’
‘1’
‘1’
‘1’
‘1’
Example: N = 4
C37.94 Frame
(mapped in
E1 Frame)
E1 Frame
E1: HDB3 Encoding
:
replace 4 zeros with 000V or B00V
...0000...
...000V...
...B00V...
T1: B8ZS Encoding
:
replace 8 zeros with 000VB0VB
...00000000...
...000VB0VB...
