RFX144V24-S23 and RFX96V24-S23 Modem Designer’s Guide
1070
8-11
8.3 ERROR CORRECTION CODING AND ARAM MESSAGE STORAGE
The host enables voice encoder error correction coding by setting control bit HDLC (7:0) prior to message encoding.
Optional error correction coding allows message storage in audio-grade random access memories (ARAMs) at an average
rate of less than 3.15 kbps or at a fixed rate of 5.0 kbps.
ARAMs must be mapped to identify those regions designated unsuitable for storing encoded message data. The address of
the unsuitable regions require error free storage locations in the ARAM. The size of this address storage location specifies
the maximum number of unsuitable regions an ARAM may have.
An unsuitable ARAM segment begins with two bad bits separated by less than 30 good bits and ends at the first bad bit
followed by 30 good bits. Unsuitable ARAM regions are defined by these ARAM segments. Examples of unsuitable regions
for a 4 Mbit (1M x 4) ARAM are the segment itself, the row of 4096 bits containing the segment, and the entire ARAM
containing at least one segment.
Additionally, the number of bad bits in the suitable ARAM region should not exceed 0.1% of the total number of bits in that
region. Use of bad bits in excess of 0.1% is not prohibited, but playback quality will gradually decrease as the percentage
increases.
8.4 ROOM MONITOR
Room Monitor allows the remote-end user to monitor the local room activity by listening to audio captured by the microphone
connected to the XIA input or, in the absence of the XIA, to the IIA input. Room monitor operation is available in all voice
codec modes and audio codec modes with DTMF detect, tone detect, and tone transmit features. Room Monitor volume
control is provided in 6 dB steps to improve monitoring capability (see parameter 68 in Section 4-2). Room monitor without
XIA is entered by setting control bit RMM (07:5) prior to mode configuration. Room monitor with the XIA is entered by setting
control bits RMM and CODECS (07:6) prior to mode configuration.
With the XIA present, the Line In connects to the IIA input, the Line Out connects to the IIA output, the Microphone In
connects to the XIA input, and the Speaker Out connects to the XIA output. A typical Room Monitor session with XIA may
proceed as follows:
1. The remote-end user is greeted by an outgoing message (OGM) from the voice or audio decoder. The remote-end user
sends a known DTMF sequence requesting Room Monitor that is received and detected.
2. Control bits RMM and CODECS are set and voice or audio codec configuration selected. An OGM is sent informing the
remote-end user of the available options. For example, “Room Monitor Enabled. Press 1 to increase volume. Press 2 to
record. Press 3 to end recording. Press 4 to end Room Monitor. <BEEP>.”
3. The remote-end user responds, the DTMF signal is detected, and the proper action initiated.
Note that tone transmission while recording with either the voice encoder or audio encoder will transmit the dual/single tone
to both the IIA and XIA output. When not recording, tone transmission will transmit the dual/single tone to the IIA output.
Room Monitor without the XIA requires that the IIA input be switched between the Line In and Microphone In as needed, and
the Line Out connected to the IIA output. Since during Room Monitor the IIA input is connected to the Microphone In, there
can be no DTMF or tone detection. For DTMF or tone detection to occur, at regular intervals the Room Monitor must be
disabled, the IIA input switched to Line In, and the configuration made to voice codec or audio codec mode. Now an OGM
may be sent and the remote-end user’s response detected. A typical Room Monitor session without XIA may proceed as
follows:
1. The remote-end user is greeted by an OGM from the voice or audio decoder. The remote-end user sends a DTMF
sequence requesting Room Monitor that is received and detected.
2. An OGM is sent requesting the remote-end user to specify a Room Monitor period. For example, “Enter the Room
Monitor period. Enter the number of seconds then press *. <BEEP>.”
3. The remote-end user responds, the DTMF signals are detected, and a timer is initialized.
4. An OGM is sent informing the remote-end user of the available options. For example, “Room Monitor Enabled. Press 1
to increase volume. Press 2 to record. Press 3 to end recording. Press 4 to end Room Monitor. <BEEP>.”
5. The remote-end user responds and the DTMF signal is detected. The IIA input is switched to the Microphone In, control
bit RMM is set, and voice or audio codec configuration selected. The timer is started and the proper action initiated.
6. Short tone bursts may be sent at regular intervals to inform the remote-end user that the Room Monitor period is
counting down , “<BEEP>“.
Содержание RFX144V24-S23
Страница 64: ...RFX144V24 S23 and RFX96V24 S23 Modem Designer s Guide 3 30 1070 This page is intentionally blank...
Страница 92: ...RFX144V24 S23 and RFX96V24 S23 Modem Designer s Guide 5 10 1070 This page is intentionally blank...
Страница 110: ...RFX144V24 S23 and RFX96V24 S23 Modem Designer s Guide 7 8 1070 This page is intentionally blank...
Страница 156: ...RFX144V24 S23 and RFX96V24 S23 Modem Designer s Guide 9 34 1070 This page intentionally left blank...
Страница 170: ...RFX144V24 S23 and RFX96V24 S23 Modem Designer s Guide 11 8 1070 This page is intentionally blank...
Страница 178: ...RFX144V24 S23 and RFX96V24 S23 Modem Designer s Guide 12 8 1070 This page is intentionally blank...
Страница 184: ...RFX144V24 S23 and RFX96V24 S23 Modem Designer s Guide 13 6 1070 This page intentionally left blank...
Страница 197: ......