MT8971B/72B
In DIGITAL NETWORK (DN) mode, upon entering
the DNIC from the DV and CD ports, the B-channel
data, D-channel D0 (and D1 for 160 kbit/s), the HK
bit of the C-channel (160kbit/s only) and a SYNC bit
are combined in a serial format to be sent out on the
line by the Transmit Interface (Figures 11, 12). The
SYNC bit produces an alternating 1-0 pattern each
frame in order for the remote end to extract the frame
alignment from the line. It is possible for the remote
end to lock on to a data bit pattern which simulates
this alternating 1-0 pattern that is not the true SYNC.
To decrease the probability of this happening the
DNIC may be programmed to put the data through a
prescrambler that scrambles the data according to a
predetermined polynomial with respect to the SYNC
bit. This greatly decreases the probability that the
SYNC pattern can be reproduced by any data on the
line. In order for the echo canceller to function
correctly, a dedicated scrambler is used with a
scrambling algorithm which is different for the SLV
and MAS modes. These algorithms are calculated in
such a way as to provide orthogonality between the
near and far end data streams such that the
correlation between the two signals is very low.
For any two DNICs on a link, one must be in SLV
mode with the other in MAS mode. The scrambled
data is differentially encoded which serves to make
the data on the line polarity-independent. It is then
biphase encoded as shown in Figure 10. See “Line
Interface” section for more details on the encoding.
Before leaving the DNIC the differentially encoded
biphase data is passed through a pulse-shaping
bandpass transmit filter that filters out the high and
low frequency components and conditions the signal
for transmission on the line.
The composite transmit and receive signal is
received at L
IN
. On entering the DNIC this signal
passes through a Precanceller which is a summing
amplifier and lowpass filter that partially cancels the
near-end signal and provides first order antialiasing
for the received signal. Internal, partial cancellation
of the near end signal may be disabled by holding
F0
C4
A
AAAAA
AAAAA
AAAAAAAAAAAA AAAAAAAA
AAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAA
AAAA
AA
AAAAAAAAAAAAAA AAAAAAAAAA
AA
AAAAAAAAAAAAA AAAAAAAAA
AAAA
AA
A
AAAAAAAAAAAA AAAAAAAA
AAAAAAAAAAA
AAAA
AA
AA
AAAAAAAAAAAAAA AAAAAAAAA
AAAA
AA
AA
AAAAA
A
AAAAAAAAAAA AAAAAAAA
AAAA
AA
AAAAAAAAAAAAA AAAAAAAAA
AAAA
AA
AA
CDSTo
AAAAA
C
0
C
1
C
2
C
3
C
4
C
5
C
6
C
7
AAAAAAAAAAAA AAAAAAAA
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
AA AAAAAAAAA AAAAAAAAA
C
0
A
AAAAA
AAAAAAAAAAAA AAAAAAAA
AAAAAAAAAAA
AAAA
AA
AA
AAAAAAAAAAAAA AAAAAAAAA
AAAA
AA
AA
A
AAAAA
AAAAAAAAAAAA AAAAAAAA
AAAAAAAAAAA
AAAA
AA
AA
AAAAAAAAAAAAA AAAAAAAAA
AAAA
AA
AA
A
AAAAA
AAAAA
AAAAAAAAAAAA
AAAAAAAAAAA
AAAA
AA
AA
AAAA
AAAA
AA
A
AA
A
AAAAAAAAAAAAAAAAAAAAAAA
AA AAAAAAAAAAAAAAAAAAAAA
AA
AAAAA
AAAAAAAAAAA AAAAAAAA
AAAA
AA
AAAA AAAAAAAAA AAAAAAAAAA
AAAA
AA
A
AAAAA
AAAAAAAAAAA AAAAAAAA
AAAA
AA
AAAA AAAAAAAAA AAAAAAAAAA
AAAAAAAAAAAAAA AAAAAAAAA
AA
A
AAAAA
C C C C C C C C
AAAAAAAAAAAAAAAAAAAAAAA
AAAAAAAAAAAA AAAAAAAA
D D D D D D D D
AA AAAAAAAAAAAAAAAAAAAAA
C
AAAAAAAAAAA AAAAAAAA
AAAA
AA
AA
AAAAAAAAAAAAA AAAAAAAAA
AAAA
AA
A
AAAAA
0
AAAAAAAAAAA
AAAA
AA
AAAAAAAAAAAAAA AAAAAAAAA
0
AAAA
AA
AA
1
2
3
4
5
6
7
AAAAAAAAAAAA AAAAAAAA
0
1
2
3
4
5
6
7
AA
A
AAAAA
AAAAAAAAAAAA AAAAAAAA
AA
AA
AAAAAAAAAAA
AAAA
AA
AAAAAAAAAAAAA AAAAAAAAA
AAAA
A
AA
A
AAAAA
AAAAAAAAAAAA
AAAAAAAAAAA
AAAA
AA
AA
AAAAAAAAAAAAA
AAAA
AA
AA
A
AAAAA
AAAAAAAAAAAA
AA
AAAA
AA
CDSTi
F0o
3.9
µsec
62.5
µsec
125
µsec
Channel Time 0
Channel Time 16
Figure 7 - CD Port (Modes 2,6)
CLD
TCK
CDi
C
6
C
7
C
0
C
1
C
2
C
3
C
4
C
5
C
6
C
7
C
0
C
1
CDo
C
6
C
7
C
0
C
1
C
2
C
3
C
4
C
5
C
6
C
7
C
0
C
1
Figure 8 - CD Port (Modes 1,5)
9-112
MITEL [ MITEL NETWORKS CORPORATION ]
