Basic troubleshooting steps
Issues caused by the IP network
The first thing to look at is a packet capture of a problem call. Ideally this should be captured as close as possible to where the problem is experienced. Depending on where the network capture is ebing taken this can be performed using the packet capture build into the Vega Gateways, packet capture built into other network equipment, or a mirrored switch port and a computer running Wireshark.
Once you have your pcap the first thing to do is to analyse the RTP streams and ensure there is no significant packet loss or jitter. These can both lead to audio issues and point at issues within the IP network being used for the call. These network issues should be resolved before proceeding further.
Issues on analogue gateways
There are a number of configuration options which will affect the transmission of audio on analogue gateways. Experimenting with these settings may solve your issue:
Impedance - it is vital that the impedance configured on the Vega Gateway matches the equipment which it is connected to. In most cases this will be set automatically if the country is configured correctly. Some equipment may not match the standard for that country so changing the impedance can help with echo and bad audio quality.
Echo canceller - the echo canceller is configured to give the best performance in the majority of scenarios. In some circumstances it may be necessary to optimise the settings for a particular environment.
disable the EC - to see if the EC is causing problems try disabling it and observe the effect
comfort noise - enabling or disabling the comfort noise can have a major effect on the perceived voice quality in certain situations
echo tail length - try setting the EC tail length to the maximum and observe the effects
Gains - gain levels can be altered to give the best audio quality
SIP Rx Gain - this affects the audio volume received from the IP side of the call
SIP Tx Gain - this affects the audio volume transmitted on the IP side of the call
Issues on digital gateways
Due to the nature of the transmission there are far fewer opportunities for audio issues to be experienced on digital gateways. If there are issues these settings can be worth experimenting with:
Echo canceller - the echo canceller is configured to give the best performance in the majority of scenarios. In some circumstances it may be necessary to optimise the settings for a particular environment.
disable the EC - to see if the EC is causing problems try disabling it and observe the effect
comfort noise - enabling or disabling the comfort noise can have a major effect on the perceived voice quality in certain situations
echo tail length - try setting the EC tail length to the maximum and observe the effects
Gains - gain levels can be altered to give the best audio quality
SIP Rx Gain - this affects the audio volume received from the IP side of the call
SIP Tx Gain - this affects the audio volume transmitted on the IP side of the call
Layer 1 companding - in the vast majority of cases a T1 will use mu-law companding and an E1 will use a-law. This is automatically configured but in some rare cases changing the default configuration will solve audio issues.