AT&T 7300 series 24th-Channel Signaling, ⎜ Channels 24th Channel ⎜ 24th Channel, Esf, ⎜ Frame No

MULTIPLEXED COMMUNICATION 1-27

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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

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⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

⎜ Channels

⎜

24th Channel

⎜ 24th Channel

⎜⎜

Channels

⎜ 24th Channel

⎜ 24th Channel

⎜

⎜

1-23

⎜

D4

⎜

ESF

⎜⎜

1-23

⎜

D4

⎜

ESF

⎜

⎜ Frame No.

⎜

Frame No.

⎜

Frame No.

⎜⎜

Frame No.

⎜

Frame No.

⎜

Frame No.

⎜

⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

⎜

1

⎜

1

⎜

13

⎜⎜

13

⎜

1

⎜

1

⎜

⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

⎜

2

⎜

2

⎜

14

⎜⎜

14

⎜

2

⎜

2

⎜

⎜

3

⎜

3

⎜

15

⎜⎜

15

⎜

3

⎜

3

⎜

⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

4

4

16

16

4

4

⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

5

5

17

17

5

5

⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

⎜

6

⎜

6

⎜

18

⎜⎜

18

⎜

6

⎜

6

⎜

⎜

7

⎜

7

⎜

19

⎜⎜

19

⎜

7

⎜

7

⎜

⎜

8

⎜

8

⎜

20

⎜⎜

20

⎜

8

⎜

8

⎜

⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

9

9

21

21

9

9

⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

10

10

22

22

10

10

⎜

⎜

⎜

⎜⎜

⎜

⎜

⎜

⎜

11

⎜

11

⎜

23

⎜⎜

23

⎜

11

⎜

11

⎜

⎜

12

⎜

12

⎜

24

⎜⎜

24

⎜

12

⎜

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