MT9074
Advance Information
appropriate mode and Jitter attenuation capability of
the MT9074
The most significant bit of an eight bit ST-BUS
channel is numbered bit 7 (see Mitel Application
Note MSAN-126). Therefore, ST-BUS bit 7 is
synonymous with DS1 bit 1; bit 6 with bit 2: and so
on.
The Digital Interface
T1 Digital Interface
Frame and Superframe Structure in T1 mode
In T1 mode DS1 frames are 193 bits long and are
transmitted at a frame repetition rate of 8000 Hz,
which results in an aggregate bit rate of 193 bits x
8000/sec= 1.544 Mbits/sec. The actual bit rate is
1.544 Mbits/sec +/-50 ppm optionally encoded in
B8ZS format. The Zero Suppression control register
(page 1, address 15H,) selects either B8ZS
encoding, forced one stuffing or alternate mark
inversion (AMI) encoding. Basic frames are divided
into 24 time slots numbered 1 to 24. Each time slot is
8 bits in length and is transmitted most significant bit
first (numbered bit 1). This results in a single time
slot data rate of 8 bits x 8000/sec. = 64 kbits/sec.
Multiframing
In T1 mode, DS1 trunks contain 24 bytes of serial
voice/data channels bundled with an overhead bit.
The frame overhead bit contains a fixed repeating
pattern used to enable DS1 receivers to delineate
frame boundaries. Overhead bits are inserted once
per frame at the beginning of the transmit frame
boundary. The DS1 frames are further grouped in
bundles of frames, generally 12 (for D4 applications)
or 24 frames (for ESF - extended superframe
applications) deep. Table 7 and 8 illustrate the D4
and ESF frame structures respectively.
For D4 links the frame structure contains an
alternating 101010... pattern inserted into every
second overhead bit position. These bits are
intended for determination of frame boundaries, and
they are referred to as Ft bits. A separate fixed
pattern, repeating every superframe, is interleaved
with the Ft bits. This fixed pattern (001110), is used
to delineate the 12 frame superframe. These bits are
referred to as the Fs bits. In D4 frames # 6 and #12,
the LSB of each channel byte may be replaced with
A bit (frame #6) and B bit (frame #12) signalling
information.
It should be noted that the Mitel ST-BUS has 32
channels numbered 0 to 31. When mapping to the
DS1 payload only the first 24 time slots and the last
(time slot 31, for the overhead bit) of an ST-BUS are
used (see Table 6). All unused channels are tristate.
When signalling information is written to the MT9074
in T1 mode 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 channels
streams are used to transmit the signalling bits.
For ESF links the 6 bit framing pattern 001011,
inserted into every 4th overhead bit position, is used
to delineate both frame and superframe boundaries.
Frames #6, 12, 18 and 24 contain the A, B, C and D
signalling bits, respectively. A 4 kHz data link is
embedded in the overhead bit position, interleaved
between the framing pattern sequence (FPS) and the
transmit CRC-6 remainder (from the calculation done
on the previous superframe), see Table 8.
Since the maximum number of signalling bits
associated with any channel is 4 (in the case of
ABCD), only half a CSTi channel is required for
sourcing the signaling bits. The choice of which half
of the channel to use is selected by the control bit
MSN (page 01H address 14H). The same control bit
selects which half of the CSTo channel will contain
receive signaling information (the other nibble in the
channel being tristate). Unused channels are tristate.
DS1 Timeslots
1
0
2
1
3
2
4
3
5
4
6
5
7
6
8
7
9
7
10 11 12 13 14 15 16
Voice/Data Channels
(DSTi/o and CSTi/o)
9
10 11 12 13 14 15
Ds1 Timeslots
17 18 19 20 21 22 23 24
-
-
-
-
-
-
-
-
Voice/Data Channels
(DSTi/o and CSTi/o)
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
x
x
x
x
x
x
x
S
bit
Table 6 - STBUS vs. DS1 to Channel Relationship(T1)
14
MITEL [ MITEL NETWORKS CORPORATION ]
