8.4.  Application Models

• 8.4.1.  How to Set Up the ECR Bridge
• Example

• 8.4.2.  How to Set Up an ECR Play Over the SCbus
• Example

Two application models are provided in this section to illustrate building an echo-cancelled connection via the SCbus.

8.4.1.  How to Set Up the ECR Bridge

This application model uses two Modular Station Interface (MSI/SC) station devices connected via the SCbus to two voice channel devices. The voice channel devices are operating in ECR mode. Two telephones are connected to the MSI/SC stations for providing input and for listening to the echo-cancelled output of each voice device.

1. Get SCbus transmit time slots of both MSI/SC devices and the ECR transmit time slots of the two voice channel devices.

ms_getxmitslot (MS1, &MS1_TX);  
   
ms_getxmitslot (MS2, &MS2_TX);  
   
dx_getxmitslotecr (CH1, &CH1_ECR_TX);  
   
dx_getxmitslotecr (CH2, &CH2_ECR_TX);

2. Have both MSI/SC stations listen to the ECR transmit of the opposite voice channel.

ms_listen (MS1, &CH2_ECR_TX);  
ms_listen (MS2, &CH1_ECR_TX);

3. Have both voice channel devices listen to their corresponding MSI/SC station device.

dx_listen (CH1, &MS1_TX);  
dx_listen (CH2, &MS2_TX);

4. Have each voice channel connect its echo canceller's receive time slot to the opposite echo canceller's ECR transmit. These signals are used as echo-reference signals.

dx_listenecr (CH1, & CH2_ECR_TX);  
dx_listenecr (CH2, & CH1_ECR_TX);

Figure 21.  ECR Bridge Example Diagram

Example

#include <stdio.h>  
#include <windows.h>  
#include <srllib.h>  
#include <dxxxlib.h>  
#include <msilib.h>  
#include <errno.h>  
main()  
{  
   int chdev1, chdev2;          /* Voice channel device handles */  
   int msdev1, msdev2;          /* MSI/SC station device handles */  
   SC_TSINFO  sc_tsinfo;        /* SCbus time slot information structure */  
   long scts;                   /* Pointer to SCbus time slot */  
   long ms1txts, ms2txts,       /* Transmit time slots of stations 1 & 2 */  
        ch1ecrtxts, ch2ecrtxts; /* Transmit time slots of echo cancellers on voice channels 1 & 2 */   
     
   /* Open voice board 1 channel 1 device */  
   if ((chdev1 = dx_open("dxxxB1C1", 0)) == -1) {  
       printf("Cannot open channel dxxxB1C1.  errno = %d", errno);  
       exit(1);  
   }  
   /* Open voice board 1 channel 2 device */  
   if ((chdev2 = dx_open("dxxxB1C2", 0)) == -1) {  
       printf("Cannot open channel dxxxB1C2.  errno = %d", errno);  
       exit(1);  
   }  
   /* Open MSI/SC board 1 station 1 device */  
   if ((msdev1 = ms_open("msiB1C1", 0)) == -1) {  
       printf("Cannot open station msiB1C1.  errno = %d", errno);  
       exit(1);  
   }  
   /* Open MSI/SC board 1 station 2 device */  
   if ((msdev2 = ms_open("msiB1C2", 0)) == -1) {  
       printf("Cannot open station msiB1C2.  errno = %d", errno);  
       exit(1);  
   }  
   /* Initialize an SCbus time slot information */  
   sc_tsinfo.sc_numts = 1;  
   sc_tsinfo.sc_tsarrayp = &scts;  
     
   /* Get SCbus time slot connected to transmit of MSI/SC station 1 on board 1 */  
   if (ms_getxmitslot(msdev1, &sc_tsinfo) == -1) {  
       printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev1), ATDV_NAMEP(msdev1));  
       exit(1);  
   }  
   ms1txts = scts;  
   /* Get SCbus time slot connected to transmit of MSI/SC station 2 on board 1 */  
   if (ms_getxmitslot(msdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev2), ATDV_NAMEP(msdev2));  
      exit(1);  
   }  
   ms2txts = scts;  
   /* Get SCbus time slot connected to transmit of voice channel 1 on board 1 */  
   if (dx_getxmitslotecr(chdev1, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
      ch1ecrtxts = scts;  
   /* Get SCbus time slot connected to transmit of voice channel 2 on board 1 */  
   if (dx_getxmitslotecr(chdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }   
   ch2ecrtxts = scts;  
   /* Have MSI/SC station 1 listen to channel 2's echo-cancelled transmit */  
   if (ms_listen(msdev1, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev1), ATDV_NAMEP(msdev1));  
      exit(1);  
   }  
   scts = ch1ecrtxts;  
   /* Have MSI/SC station 2 listen to channel 1's echo-cancelled transmit */  
   if (ms_listen(msdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev2), ATDV_NAMEP(msdev2));  
      exit(1);  
   }  
   scts = ms1txts;  
   /* Have channel 1 listen to station 1's transmit */  
   if (dx_listen(chdev1, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
   scts = ms2txts;  
   /* Have channel 2 listen to station 2's transmit */  
   if (dx_listen(chdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }  
   scts = ch2ecrtxts;  
   /* Have channel 1's echo canceller listen to channel 2's echo-cancelled transmit */  
   if (dx_listenecr(chdev1, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
   scts = ch1ecrtxts;  
   /* Have channel 2's echo canceller listen to channel 1's echo-cancelled transmit */  
   if (dx_listenecr(chdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }  
   /* Bridge connected, both stations receive echo-cancelled signal */  
   /*   
    *  
    * Continue  
    *  
    */  
   /* Then perform xx_unlisten() and dx_unlistenecr(), plus all necessary xx_close()s */  
   if (ms_unlisten(msdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev2), ATDV_NAMEP(msdev2));  
      exit(1);  
   }  
   if (ms_unlisten(msdev1) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev1), ATDV_NAMEP(msdev1));  
      exit(1);  
   }  
   if (dx_unlistenecr(chdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }  
   if (dx_unlistenecr(chdev1) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
   if (dx_unlisten(chdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }  
   if (dx_unlisten(chdev1) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
   if (dx_close(chdev1) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
   if (dx_close(chdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }  
   if (ms_close(msdev1) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
   if (ms_close(msdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev2), ATDV_NAMEP(msdev2));  
      exit(1);  
   }  
   return(0);  
}




8.4.2.  How to Set Up an ECR Play Over the SCbus

In this model, two MSI/SC station devices are connected via the SCbus to two voice channel devices. The second voice channel device is operating in ECR mode. Two telephones are connected to the MSI/SC stations for providing input and listening to the echo-cancelled output of the second voice device, and to the non-echo-cancelled output of the first voice device.

1. Get SCbus transmit time slots of both MSI/SC devices and the ECR transmit time slots of the two voice channel devices.

ms_getxmitslot (MS1, &MS1_TX);  
dx_getxmitslot (CH1, &CH1_TX);  
dx_getxmitslotecr (CH2, &CH2_ECR_TX);

2. Have the MSI/SC station 1 listen to the transmit (TX) of channel 1.

ms_listen (MS1, & CH1_TX);

3. Have MSI/SC station 2 listen to the ECR transmit of channel 2.

ms_listen (MS2, & CH2_ECR_TX);

4. Have voice channel 2 listen to MSI/SC station 1's transmit.

dx_listen (CH2, & MS1_TX);

5. Have voice channel 2 connect its echo canceller's receive time slot to transmit of channel 1. This signal is used as the echo-reference signal.

dx_listenecr (CH2, & CH1_TX);

Figure 22.  An ECR Play Over the SCbus

Example

#include <stdio.h>  
#include <windows.h>  
#include <srllib.h>  
#include <dxxxlib.h>  
#include <msilib.h>  
#include <errno.h>  
main()  
{  
   int chdev1, chdev2;        /* Voice channel device handles */  
   int msdev1, msdev2;        /* MSI/SC station device handles */  
   SC_TSINFO  sc_tsinfo;      /* SCbus time slot information structure */  
   long scts;                 /* Pointer to SCbus time slot */  
   long ms1txts,              /* Transmit time slots of stations 1 & 2 */   
        ch1txts, ch2ecrtxts;  /* Transmit time slots of echo cancellers on  
                                 voice channels 1 & 2 */   
     
   /* Open voice board 1 channel 1 device */  
   if ((chdev1 = dx_open("dxxxB1C1", 0)) == -1) {  
       printf("Cannot open channel dxxxB1C1.  errno = %d", errno);  
       exit(1);  
   }  
   /* Open voice board 1 channel 2 device */  
   if ((chdev2 = dx_open("dxxxB1C2", 0)) == -1) {  
       printf("Cannot open channel dxxxB1C2.  errno = %d", errno);  
       exit(1);  
   }  
   /* Open MSI/SC board 1 station 1 device */  
   if ((msdev1 = ms_open("msiB1C1", 0)) == -1) {  
       printf("Cannot open station msiB1C1.  errno = %d", errno);  
       exit(1);  
   }  
   /* Open MSI/SC board 1 station 2 device */  
   if ((msdev2 = ms_open("msiB1C2", 0)) == -1) {  
       printf("Cannot open station msiB1C2.  errno = %d", errno);  
       exit(1);  
   }  
   /* Initialize an SCbus time slot information */  
   sc_tsinfo.sc_numts = 1;  
   sc_tsinfo.sc_tsarrayp = &scts;  
     
   /* Get SCbus time slot connected to transmit of voice channel 1 on board 1 */  
   if (ms_getxmitslot(msdev1, &sc_tsinfo) == -1) {  
   printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev1), ATDV_NAMEP(msdev1));  
       exit(1);  
   }  
   ms1txts = scts;  
   /* Get SCbus time slot connected to transmit of voice channel 1 on board 1*/  
   if (dx_getxmitslot(chdev1, &sc_tsinfo) == -1) {  
   printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
   ch1txts = scts;  
   /* Get SCbus time slot connected to transmit of voice channel 1 on board 1 */  
   if (dx_getxmitslotecr(chdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }   
   ch2ecrtxts = scts;  
   /* Have station 1 listen to file played by voice channel 1 */  
   scts = ch1txts;  
   if (ms_listen(msdev1, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev1), ATDV_NAMEP(msdev1));  
      exit(1);  
   }  
   /* Have station 2 listen to echo-cancelled output of voice channel 2 */  
   scts = ch2ecrtxts;  
   if (ms_listen(msdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev2), ATDV_NAMEP(msdev2));  
      exit(1);  
   }  
   /* Have voice channel 2 listen to echo-carrying signal from station 1 */  
   scts = ms1txts;  
   if (dx_listen(chdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
     
   /* And activate the ECR feature on voice channel 2, with the echo-reference signal   
      coming from voice channel 1 */  
   scts = ch1txts;  
   if (dx_listenecr(chdev2, &sc_tsinfo) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }  
   /* Setup completed, any signal transmitted from channel device 1,  
    *  will a) be received by station 1,  
    *       b) contribute echo to the transmit of station 1,  
    *       c) will be heard AFTER echo cancellation (on channel 2) by   
    *          station 2.*/  
   /*   
   .  
   . Continue  
   .  
   */  
   /* Then perform xx_unlisten() and dx_unlistenecr(), plus all necessary xx_close()s */  
   if (ms_unlisten(msdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev2), ATDV_NAMEP(msdev2));  
      exit(1);  
   }  
   if (ms_unlisten(msdev1) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev1), ATDV_NAMEP(msdev1));  
      exit(1);  
   }  
   if (dx_unlistenecr(chdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), TDV_NAMEP(chdev2));  
      exit(1);  
   }  
   if (dx_unlisten(chdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }  
   if (dx_close(chdev1) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev1), ATDV_NAMEP(chdev1));  
      exit(1);  
   }  
   if (dx_close(chdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(chdev2), ATDV_NAMEP(chdev2));  
      exit(1);  
   }  
   if (ms_close(msdev1) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev1), ATDV_NAMEP(msdev1));  
      exit(1);  
   }  
   if (ms_close(msdev2) == -1) {  
      printf("Error message = %s, on %s", ATDV_ERRMSGP(msdev2), ATDV_NAMEP(msdev2));  
      exit(1);  
   }  
   return(0);  
}

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