The Analog Voice Module, Voice Expansion modules and the Universal Analog Voice Module, hereafter referred to in general as the voice modules, are an integral part of the Passport 4400 unit. As shown in the following illustration, voice modules convert analog voice obtained from telephone interfaces into digital form, and internally connect the converted voice to the Ethernet Base Module within the unit. In addition, each voice call may include dialing information that specifies the destination address of the call. Next, the converted digitized signal is multiplexed with other data to form part of the composite data stream. This data stream is transmitted over a Passport network to a remote Passport 4400 unit.
At the remote unit, the digitized voice signal is demultiplexed and routed to a compatible voice channel specified by the destination address. Ultimately, the digitized voice signal is reconverted to the original analog form.
In addition to accepting analog voice signals for digital conversion, the voice modules can also process analog signals obtained from a fax machine. This feature is implemented by firmware resident within each voice channel.
The firmware constantly monitors the incoming analog stream for the presence of fax signals. When fax signals are detected, the firmware switches the voice channel from the voice mode into the fax mode. While in this mode, the signals are demodulated into the appropriate fax symbols and passed as data to the remote end. At the remote end the symbols are remodulated.
The following topics are discussed in this section:
  |
|