ATL Telecom AM64/512 User Manual
Page 30
AP PEN DIX D - Use on X.21/X.21bis dig i tal cir cuits
Appendix E - Pri vate dig i tal cir cuits
The de tails in this ap pen dix re late to the ar range ment shown in fig ure E.1 be low ;
The main dif fer ence be tween this ar range ment and the con ven tional link is the need for a spe cial in ter face ca -
ble which joins the mas ter BBM to the pri vate dig i tal cir cuit. This ca ble is con fig ured to ex tract the tim ing sig -
nal from the pri vate dig i tal cir cuit and syn chro nise the BBM link to this clock.
There are 2 pos si ble types of syn chro ni sa tion; bit tim ing and byte tim ing. The bit tim ing mode en sures cor rect
trans fer of data across the link but there is no byte align ment be tween the ends. The byte tim ing mode en -
sures align ment of ev ery oc tet of data. The bit tim ing mode is avail able for ev ery in ter face type and user rate,
but the byte tim ing mode is only avail able for X.21 at 64kbit/s.
Please see ta ble be low show ing ex pected system per for mance on var i ous wire gauges :
Wire Gauge mm
Trans mis sion Dis tance in km
64K Line Rate
High Speed 512k Line Rate
0.32
5.8
3.4
0.40
6.5
3.6
0.51
8.6
5.0
0.64
10.8
6.4
0.90
17.5
8.9
It is im por tant that the ca bles are con nected cor rectly, (see di a gram). The ca ble de tails are given be low:
1. X.21 bit tim ing ca ble - (15 way to 15 way D type plugs).
CCITT cir cuit
Tim ing Source (DCE)
Tim ing Sink (DTE)
CCITT cir cuit
T-A
2
4
R-A
T-B
9
11
R-B
R-A
4
2
T-A
R-B
11
9
T-B
S-A
13
1
SEXT-A
S-B
6
15
SEXT-B
I-A
5
3
C-A
I-B
12
10
C-B
C-A
3
5
I-A
C-B
10
12
I-B
GND
8
8
GND
A-10
a
telecom
User Guide
High Speed Mo dems
Pri vate
digi tal
X.21/X.21bis
cir cuit
(Tim ing
source)
DCE
end
Ex ter nal tim ing
in ter face ca ble
BBM Mas ter
(Tim ing sink)
DTE
end
2- wire
line
BBM Slave
Stan dard
X.21/X.21 bis
ca ble
DTE
Figure E.1