![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT75R12DIB-L_datasheet_100141/XRT75R12DIB-L_99.png)
XRT75R12D
95
REV. 1.0.3
TWELVE CHANNEL E3/DS3/STS-1 LINE INTERFACE UNIT WITH SONET DESYNCHRONIZER
Figure 43 was copied directly out of Telcordia GR-253-CORE. However, this figure can be simplified and
redrawn as depicted below in Figure 44.
FIGURE 43. AN ILLUSTRATION OF TELCORDIA GR-253-CORE'S RECOMMENDATION ON HOW MAP DS3 DATA INTO
AN
STS-1 SPE
FIGURE 44. A SIMPLIFIED "BIT-ORIENTED" VERSION OF TELCORDIA GR-253-CORE'S RECOMMENDATION ON HOW
TO MAP
DS3 DATA INTO AN STS-1 SPE
For DS3 Mapping, the STS-1 SPE has the following structure.
25I
I
C3
R
25I
I
C2
R
25I
C1
R
25I
I
C3
R
25I
I
C2
R
25I
C1
R
25I
I
C3
R
25I
I
C2
R
25I
C1
R
25I
I
C3
R
25I
I
C2
R
25I
C1
R
25I
I
C3
R
25I
I
C2
R
25I
C1
R
25I
I
C3
R
25I
I
C2
R
25I
C1
R
25I
I
C3
R
25I
I
C2
R
25I
C1
R
25I
I
C3
R
25I
I
C2
R
25I
C1
R
25I
I
C3
R
25I
I
C2
R
25I
C1
R
POH
87 bytes
R = [r, r, r, r, r, r, r, r]
I = [i, i, i, i, i, i, i, i]
C1 = [r, r, c, i, i, i, i, i]
C2 = [c, c, r, r, r, r, r, r]
C3 = [c, c, r, r, o, o, r, s]
i = DS3 data
r = fixed stuff bit
c = stuff control bit
s = stuff opportunity bit
o = overhead communications channel bit
Fixed
Stuff
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
208i
s
1r
2o
2r
2c
16r
208i
6r
2c
16r
205i
c
18r
r
c
s
i
o
- Fixed Stuff Bits
- Stuff Control/Indicator Bits
- DS3 Data Bits
- Stuff Opportunity Bits
- Overhead Communication Bits
POH