Preliminary Information
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
MT9173/74
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
F0
C4
CDSTo
C
0
C
1
C
2
C
3
C
4
C
5
C
6
C
7
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
C
0
CDSTi
C
0
C
1
C
2
C
3
C
4
C
5
C
6
C
7
D
0
D
1
D
2
D
3
D
4
D
5
D
6
D
7
C
0
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)
9-143
MITEL [ MITEL NETWORKS CORPORATION ]
