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MT8971B Datasheet(PDF) 6 Page - Mitel Networks Corporation |
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MT8971B Datasheet(HTML) 6 Page - Mitel Networks Corporation |
6 / 20 page MT8971B/72B 9-112 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 LIN. 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 Figure 7 - CD Port (Modes 2,6) Figure 8 - CD Port (Modes 1,5) F0 C4 CDSTo CDSTi F0o C0 C1 C2 C3 C4 C5 C6 C7 C0 C1 C2 C3 C4 C5 C6 C7 D0 D1 D2 D3 D4 D5 D6 D7 D0 D1 D2 D3 D4 D5 D6 D7 C0 C0 3.9 µsec 62.5 µsec 125 µsec Channel Time 0 Channel Time 16 CLD TCK CDi CDo C0 C1 C2 C3 C4 C5 C6 C7 C6 C7 C0 C1 C0 C1 C2 C3 C4 C5 C6 C7 C6 C7 C0 C1 |
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