
Advance Information
MT9072
41
When the device is in IMA (Inverse Mux for ATM) mode, the mapping is the S-bit followed by 24 PCM channels.
This relationship is shown in Table 3. Note that the S-bit location in the Table is indicated by the bit number;
which starts from bit 0. Hence the strict definition of ST-BUS channels is not adhered to. As in a T1 interface
the data on the DSTi/o is a bit followed by 24 channels.
When signaling information is written to the MT9072 using ST-BUS control links (as opposed to direct writes by
the microport to the on-board signaling registers), the CSTi channels corresponding to the selected DSTi
channel streams are used to transmit the signaling bits. Since the maximum number of signaling bits
associated with any channel is 4 (in the case of ABCD), only half a CSTi (bits 3 to 0) channel is required for
sourcing the signaling bits. Bit A is bit 3 from the CSTi stream, Bit B is 2, Bit C is 1, and Bit D is 0. Unused
channels and unused bits are tristate.
In T1 transparent mode, the DSTi data is transparently sent to the PCM24 channels. In transparent mode the
data on the DSTi streams will appear unaltered on the PCM24 links and data received on the PCM24 link will
pass unaltered to the DSTo streams. No signaling insertion or extraction is done in transparent mode. If the
TxSYNC control bit (address Y00) is 1 then the transmit S-bit is overwritten by channel 31 bit 0 in the 2.048
Mbit/s ST-BUS mode. In the 8.192 Mbit/s ST-BUS mode the S-bits from channels 124,125,126,127 respectively
are used to override the transmit S-bit positions for Framers 0 to 3 or 4 to 7 respectively. If T1 Transparent
mode and IMA mode are both selected then the S-bit and channel bits are transparently mapped as shown in
Table 3.
PCM24 Channels
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
ST-BUS Channels
(DSTi/o and CSTi/o)
0
1
2
3
4
5
6
7
7
9
10
11
12
13
14
15
PCM24 Channels
17
18
19
20
21
22
23
24
-
-
-
-
-
-
-
S-bit
ST-BUS Channels
(DSTi/o and CSTi/o)
16
17
18
19
20
21
22
23
24
x
25
x
26
x
27
x
28
x
29
x
30
x
31
Table 1 - ST-BUS vs. PCM24 Channel Relationship for 2.048 Mbit/s DST/CST Streams (T1)
PCM24 Channels
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
ST-BUS
Chan(DSTi/o
and CSTi/o)
F0/4
F1/5
F2/6
F3/7
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
PCM24 Channels
17
18
19
20
21
22
23
24
S-bit
-
-
-
-
-
-
-
ST-BUS
Chan(DSTi/o
and CSTi/o)
F0/4
F1/5
F2/6
F3/7
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
124
125
126
127
Table 2 - ST-BUS Channel vs. PCM24 Channel Relationship for 8.192 Mbit/s DST/CST Streams (T1)
PCM24 Channels
S
bit
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
ST-BUS Channels
(DSTi/o)
Bit
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
PCM24 Channels
16
17
18
19
20
21
22
23
24
ST-BUS Channels
(DSTi/o)
15
16
17
18
19
20
21
22
23
Table 3 - ST-BUS vs. PCM24 to Channel Relationship for IMA DST Streams (T1)