what causes poor voice quality and video pixelization in a video call?

G.711 is a higher bandwidth codec than G.729 and typically offers better voice quality, so using G.711 would generally improve, not worsen, voice quality.

Using 1 Gbps network ports instead of 100 Mbps ports provides more bandwidth, which would generally improve, not degrade, voice and video quality.

Incorrect Quality of Service (QoS) configuration is a common cause of poor voice and video quality because it fails to prioritize real-time traffic (RTP streams) over less time-sensitive data. Without proper QoS, voice and video packets can experience excessive delay, jitter, and packet loss, leading to audible and visual artifacts like pixelization.

A firewall blocking RTP ports would typically prevent calls from establishing or result in one-way audio/video, rather than causing poor quality or pixelization in an active call.