White Papers Application Notes Message Waiting Indicator (MWI)
Asterisk PBX Message Waiting Indicator for Analog Lines |
Figure1: Typical analog phone with Message Waiting Indicator (MWI) neon light capability
A Message Waiting Indicator (“MWI”) is a method used on analog telephone sets to indicate a voice message has been recorded and is waiting for the recipient at that extension. Supported message indicator types include:
Asterisk PBX MWI MechanismsFor Telephones with Integrated MWIIf your telephone sets support MWI functionality, enabling it is simply a process of changing two parameters, one to enable voice mail ("VM") in the Asterisk configuration (refer to the relevant Asterisk distribution documentation for instructions) and the other in the Astribank driver.For DAHDI Version 2.4.0 and AboveFor Asterisk 1.6.x and aboveMake sure that the vmwi_ioctl parameter in the xpd_fxs module is “1” (this is the default value). Check the current definition using this command:cat /sys/modules/xpd_fxs/parameters/vmwi_ioctl If the value is 0, then the parameter is defined in one of the files in the /etc/modprobe.d and needs to be updated there. In addition, set the following parameter in the /etc/asterisk/chan-dahdi.conf file: mwisendtype=neon For Asterisk 1.4.xTo enable MWI the vmwi_ioctl parameter must be defined for the xpd_fxs driver. To do this, add the following line to the /etc/modprobe.d/xpp.conf file: options xpd_fxs vmwi_ioctl=0For Older Versions of DAHDIFor Asterisk 1.6.x and aboveMake sure that the vmwi_ioctl parameter in the xpd_fxs module is “1” (this is the default value). Check the current definition using this command:cat /sys/modules/xpd_fxs/parameters/vmwi_ioctl If the value is 0, then the parameter is defined in one of the files in the /etc/modprobe.d and needs to be updated there. In addition, set the following parameter in the /etc/asterisk/chan-dahdi.conf file: mwisendtype=neon After that, restart Asterisk and DAHDI. For Asterisk 1.4.xTo enable MWI the vmwineon and vmwi_ioctl parameters must be defined for the xpd_fxs driver. To do this, add the following line to the /etc/modprobe.d/xpp.conf file:options xpd_fxs vmwineon=1 vmwi_ioctl=0 After that, restart Asterisk and DAHDI. For Telephones without Integrated MWIIf your telephone sets are not equipped with integrated MWI functionality it is still possible to implement it using an external LED. Modern MWI mechanisms are based on a low-power Light Emitting Diode (LED) with a blocking component (like a Zener diode) that blocks line voltage which is lower than the required voltage (usually 80 to 100 Volts). See the schematic for this scenario in Figure 2, below:
Figure 2: This circuit shows how to activate MWI functionality for telephone sets that are not equipped with an integrated MWI.
To add the MWI functionality to your existing analog telephone set, simply create the above reference circuit and connect it in parallel to the telephone line. Make sure the VM function is enabled in the Asterisk configuration (refer to the relevant Asterisk distribution documentation for instructions).Popular ImplementationsMWI is popular in hotels (click here to see our hotel implementation white paper), offices, and most public telephone networks. Ease of implementation and accuracy of the MWI technology is illustrated below. The regularly oscillating signal voltage indicates the expected, clean wave shape of the electrical signal. 
Figure 3: Scope probes are x10. Line voltage is 50 volts, jumping to 90 volts every 250 milliseconds.
|
|
| Last Updated ( Sunday, 14 August 2011 ) |
Download this application note as a PDF file
