MT8972B Mitel Networks Corporation, MT8972B Datasheet - Page 6

MT8972B

Manufacturer Part Number

MT8972B

Description

(MT8971B) ISO2-CMOS ST-BUS FAMILY Digital Subscriber Interface Circuit Digital Network Interface Circuit

Manufacturer

Mitel Networks Corporation

Datasheet

1.MT8972B.pdf (20 pages)

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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.

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

9-112

CLD

TCK

CDi

CDo

CDSTo

CDSTi

F0o

In order for the echo canceller to function

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A A

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A A

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A A

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A A

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A A

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A A

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Channel Time 0

3.9 sec

62.5 sec

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Figure 7 - CD Port (Modes 2,6)

Figure 8 - CD Port (Modes 1,5)

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125 sec

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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

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

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Channel Time 16

On entering the DNIC this signal

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MT8972B Mitel Networks Corporation, MT8972B Datasheet - Page 6

MT8972B

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