I am new to voip. In my study I¡¡have one question don't understand. why use nm-hdv or vwic-2mft to telco? what i think is that the link between the voip gateway and telco is an ip link, the voice have been change to ip packet, why still need voice module? when i test voip using 2 routers with 1 fxs port on each, i don't need to have a vwic installed in gateway, just a normal data link. so why and when should use nm-hdv or vwic-2mft mode for voip? and another question is to connect pbx to voip gateway, beside fxo, e&m, is there any method to do it? thank you!
The link between the gateway and the telco is a telephony, you take the audio from the telco and you have to digitize and packetize it. And for that you would need Digital Signal Processor that are available on the NM-HDV module. Once the voice is packetized then it can be sent over the ip networks.
When you have two routers with 2 FXS ports, you have analog circuit from the telephone to the FXS port. The NM-2V in which the FXS normally sits has the DSP that will do the analog voice to digital/packetized voice packets to sent across the ip link. Try doing the show voice dsp on the router which has FXS ports and you will see the DSPs.
PBXs can be connected to voice gateways through FXO, FXS and E&M and T1 digital cards. These are basic PBX voice gateway integartion methods.
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