Table 1-8. 24Th-Channel Signaling Arrangement — Dmi Bos - AT&T DEFINITY 2500 series Network Manual

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Facilities using RBS carry digital data at 56 kbps. They can be used to carry voice, voice-grade data, or
data that uses only 56 kbps of the available 64-kbps bandwidth (for example, mode-1 data).
24th-Channel Signaling
24th-channel signaling permits the channels to use their full 64 kbps bandwidth capacity. This type of
signaling provides 23 64-kbps channels for voice or data transmission, with the 24th channel reserved for
signaling only.
The format used to carry signaling information requires a 24-frame superframe. ESF meets this
requirement. For D4 framing to meet this requirement, however, two D4 frames are linked together to form
the required 24-frame superframe.
There are three variations of 24th-channel signaling:
AT&T proprietary signaling
DMI BOS (bit-oriented signaling)
ISDN-PRI (sometimes called DMI MOS, or DMI message-oriented signaling)
Table 1-8, 24th-Channel Signaling Arrangement, depicts the frame number and signaling channel
relationship used for DMI BOS (many other relationship rotations are possible).
Table 1-8. 24th-Channel Signaling Arrangement — DMI BOS
Channels 24th Channel
1-23
Frame No. Frame No.
1
2
3
4
5
6
7
8
9
10
11
12
AT&T proprietary signaling was the first type of 24th-channel signaling provided by System 75 and
System 85. It was developed to carry DCP-formatted data (in digital form) between System 75 and/or
System 85 switches. AT&T proprietary signaling is described in the initial release of the DMI technical
specification.
For AT&T proprietary signaling, a complete set of signaling information is sent every 24 frames. This 24-
frame period is not synchronized to the 12-frame superframe format of D4 framing or to the 24-frame
superframe format of ESF framing. Each signaling byte contains the equivalent of a channel identification
24th Channel
D4 ESF
Frame No.
1 13
2 14
3 15
4 16
5 17
6 18
7 19
8 20
9 21
10 22
11 23
12 24
MULTIPLEXED COMMUNICATION
Channels 24th Channel
1-23 D4
Frame No. Frame No.
13 1
14 2
15 3
16 4
17 5
18 6
19 7
20 8
21 9
22 10
23 11
24 12
1-27
24th Channel
ESF
Frame No.
1
2
3
4
5
6
7
8
9
10
11
12