One of our customers have SX20s that sometimes display blockiness in calls.
(No gatekeeper between them)
I checked the call history of that SX20 and found there were not so much packet loss. But sometimes Video Incoming MaxJitter increased over 40, 120 at the highest. I suspect this incoming jitter caused blockiness.
Most likely jitter is caused by network devices though, is there any setting on SX20 to reduce those blockiness?
Packet loss and jitters will affect the quality of the video/audio. This could be caused by a duplex mismatch somewhere in your network. Could you check the duplex setting or port of the switch where your SX20 is connected to. Usually by default the SX20 speed is set to Auto however auto-negotiation only works if both devices are set to Auto. If the the switch is set to other settings the auto device will configure itself as 100/Half. The most common cause of mismatch issues is the scenario where one device is set to 100/Full and the other is set to Auto and will cause lot of packet loss and jitter.