I think this answer is given in the link Jens refers to above, but for your reference:
High Definition is anything that support 720p (1280x720) - which is standard on the C20's
Full HD is anything that supports 1080i/p (1920x1080) - which is only available with the Premium Resolution licence.
Without the Premium Resolution licence, the C20 can "output" a 1080p image to the screen, but will only transmit 720p to the far end.
What I don't know is what is happening internally. I.e. is the camera actually outputting a 1080p image to the CODEC via HDMI, the the CODEC is forcibly down scaling/sampling the resolution to 720p from transmission, or is the input from the Camera limited in software to 720, which means that if you output a 1080p image to the local screen you are essentially getting the CODEC to upscale the resolution (but still forcibly connecting to a remote unit using 720p).
If you have a 1080P camera, the camera and codec will work at 1080p locally. The self-view, or any content that is fed in locally, will display at 1080p. It is only the video that is transmitted to another participant that is downscaled to 720p (or lower depending on the available bandwidth) without the Premium Resolution licence.
Please remember to rate responses and to mark your question as answered if aprpopriate.
Wayne -- Please remember to rate responses and to mark your question as answered if appropriate.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.