Nortel DMS-100 Series Maintenance Manual page 87

Table 3-1 (Sheet 2 of 2)
Frame number
8
9
10
11
12
Framing bits from frames 1, 3, 5, 7, 9, and 11 are frame timing (Ft) bits.
Framing bits from frames 2, 4, 6, 8, 10, and 12 are frame signaling (Fs) bits.
When an Fs bit changes from 0 to 1 (occurs in the change from frame 4 to
frame 6), this signals the Star Hub that the sixth frame follows the 1 framing
bit. When an Fs bit changes from 1 to 0 (that occurs in the change from frame
10 to frame 12), this notifies the Star Hub that the twelfth frame follows the 0
framing bit.
It is important to identify the sixth and twelfth frames in a superframe because
these frames contain time-slot-associated signaling bits. These bits are found
on all 24 time slots of the sixth and twelfth frames in the least significant bit
position. A speech-signal bit was in this position first, but the speech-signal
bit was robbed. The speech-signal bit was replaced with a signaling bit that
depends on the direction the data is moving.
Signaling bits located in the sixth frame are called A-bits. Signaling bits
located in the twelfth frame are called B-bits.
The following figure shows the format of a DS-1 superframe.
Signaling for the Star Remote System 3-3
Framing bit type
Fs
Ft
Fs
Ft
Fs
DMS-100 Family NA100 Star Remote System XPM15 and up
Framing bit value
1
1
1
0
0