Missing half second or so initial audio

The gateway misses first two words or sometimes poses on second word for an incoming call.

This seems to be an issue only happen when VOIP/SIP is used, it does not happen when physical phone line is used. Typically, the SIP outgoing audio must travel from the gateway computer to the company router, and from router to the VOIP service (router and media gateway), and from VOIP service to PSTN network. Sometimes, there is about half second or so initial audio that may get lost in the process. This does not happen to all the calls or all the locations. For example, if you have a slow computer, and takes a little longer to generate the initial audio, then the callee may not hear any missing audio. Switch to a faster computer, you may start to have this problem.

There is not much Voicent gateway program can do to detect or solve this. According to the SIP protocol, whenever a SIP client gets the Media ready message from the VOIP service, the audio channel is open. When open, the gateway will get the audio (either audio file, dynamically generated TTS audio, or human conversation) and send it to the audio channel. The SIP audio channel usually uses UDP instead of TCP connection to improve efficiency. But it is an unreliable connection compared with TCP – media packets is not guarenteed to get to its destination. Voicent gateway and most SIP programs use lost concealment to smooth out the audio.

So what is the solution or workaround if you experience this problem? Delay the actual audio playing, assuming the first second may get lost. This workaround can not be done on the gateway since this problem does not occur on all locations.

If you have a pre-recorded audio, insert one second silence in the beginning. If you use dynamically generated TTS, add a silence audio prompt before the TTS item.

If the missing audio happens to some calls only, then add a few none-essential words at the beginning. For example, you can start your announcement like: “Welcome to ACME corporation…”