Signaling States for SLC 96 System Channel Units
Single Party i.e. "POTS"

Signaling States

Sent to the LDS Sent to the RT
Client State  A   B   A   B  Channel State
On hook 0 0 0 1 Channel Test
Off hook 1 0 1 0 Forward disconnect
Unequipped 1 1 1 1 Idle
      1 1/0¹ Ringing
¹ Bit state alternates in cadence with ringing cycle from central office.

Universal Voice Grade

(Currently not supported.
For reference only)

Signaling States

Sent to the LDS Sent to the RT
Client State  A   B   A   B  Channel State
On Hook 0 0 0 0 Ground Start
Ring Ground 0 1 0 1 Channel Test
Off hook 1 0 1 1/0¹ Ringing
Unequipped 1 1 0 1/0² Idle
¹ Bit state alternates in cadence with ringing cycle from central office.
² During idle state, the "B" bit follows a predetermined cadence

Timeslot vs. channel assignment

TR-008 uses D1D as opposed to D4 alignment

DS-1 Frame Channel Number
 Time Slot   A Shelf   B Shelf   C shelf   D Shelf 
1 1 25 49 73
2 13 37 61 85
3 2 26 50 74
4 14 38 62 86
5 3 27 51 75
6 15 39 63 87
7 4 28 52 76
8 16 40 64 88
9 5 29 53 77
10 17 41 65 89
11 6 30 54 78
12 18 42 66 90
13 7 31 55 79
14 19 43 67 91
15 8 32 56 80
16 20 44 68 92
17 9 33 57 81
18 21 45 69 93
19 10 34 58 82
20 22 46 70 94
21 11 35 59 83
22 23 47 71 95
23 12 36 60 84
24 24 48 72 96