Abstract: In a video conferencing system including stations at a plurality of different sites, and in which system first and second video channels are simultaneously displayed at each site station on a picture-in-picture video monitor, a site controller causes a video decoder at the site to decode either a video signal generated at the site or a video signal received from another site via the first video channel. The site controller also responds to a channel assignment signal generated by a system controller by assigning the first video channel to either a first predetermined broadcast frequency or to a second predetermined broadcast frequency and by assigning a second video channel carrying a video signal received from another site to the other of the first and second predetermined broadcast frequencies.

Abstract: In a system for assigning to given user terminals in a multiple-user DAMA communication system access to time slots of a time frame within which to transmit messages identified in message-access requests from different given user terminals, a plurality of message-access requests from different given user terminals are stored in a memory and then processed to schedule the identified messages for transmission.