Twilio Client requires a high speed and low latency network connection. Benchmark the network using pingtest.net or speedtest.net and aim to improve the scores.
- If your router supports QoS, prioritize UDP ports in the range 10000-20000, and the IP address of the agents making/receiving the calls. Tips on setting up QoS for VoIP in your network can be found here.
Reduce network activity not related to VoIP or use a separate network for VoIP workstations.
Chrome v38/39 has known issues of audio dropouts / one-way audio. Upgrade your browser or use Firefox and see if the issue persists.
For more information about improving call quality, please refer to this article.