ATL TELECOM USER GUIDE
AM2048A
29
Table 2 Loop-back code definitions
These loop activation codes are only detected at the G.703 interface at the ELU when CRCs
are enabled.
Loop 1 is the equivalent of a local loop at the ELU.
Loop 2 is the equivalent of a remote loop set from the ELU.
Note
: The specification did not anticipate point to multipoint so in this mode loop 2 is not
meaningful.
State
Loop-back 1
command
Loop-back 2
command
Loop-back
acknowledge
Loop-back release
command
DS-ET
<--
<--
-->
<--
Sa5
0
0
0
0
Sa6
1111
1010
xxxx
0000
4
28
ATL TELECOM USER GUIDE
AM2048A
4.10.4
ETS 300 233 Loopbacks
Loop 1 and Loop 2 may be activated by sending patterns using spare bits 5 and 6 in TS0.
Table 1 CrC4 Multi-frame Structure
Sub-
Multi-
frame
I
II
Frame
number
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Bits 1 to 8 of the PCM frame (i.e. time slot 0)
1
2
3
4
5
6
7
8
c1
0
0
1
1
0
1
1
0
1
A
Sa4
Sa5
Sa61 Sa7
Sa8
c2
0
0
1
1
0
1
1
0
1
A
Sa4
Sa5
Sa62 Sa7
Sa8
c3
0
0
1
1
0
1
1
1
1
A
Sa4
Sa5
Sa63 Sa7
Sa8
c4
0
0
1
1
0
1
1
0
1
A
Sa4
Sa5
Sa64 Sa7
Sa8
c1
0
0
1
1
0
1
1
1
1
A
Sa4
Sa5
Sa61 Sa7
Sa8
c2
0
0
1
1
0
1
1
1
1
A
Sa4
Sa5
Sa62
Sa7
Sa8
c3
0
0
1
1
0
1
1
E
1
A
Sa4
Sa5
Sa63 Sa7
Sa8
c4
0
0
1
1
0
1
1
E
1
A
Sa4
Sa5
Sa64 Sa7
Sa8
Multi-
frame
ELU
NTU
Network
ELU
NTU
Network
Loopback 1
Loopback 2
