Data services for space station Freedom

The data services that are available between the space station Freedom and the users of Freedom located on the ground are described from a user's perspective. These services consist of path service on the onboard LAN to provide minimum service and maximum throughput for telemetry, ISO protocol services on the LAN to provide robust end-to-end communications and applications services, path and bitstream services over dedicated high-rate links from payloads to communications and tracking system input ports for telemetry, audio service for two-way voice communications with the ground, and video services for two-way videoconferencing and standard video-image data. The space station will use virtual channels (VCSs) to deliver predefined data sets (packaged in a VC) to the correct destinations for data traveling in both the forward (ground-to-space) and return (space-to-ground) directions. The VC provides a means of dividing the single physical RF link into a number of smaller `virtual' links that can be reassigned as required, and also of creating a virtual link between the two end points of the VC