Abstract: A local computer 132 is connected to a remote computer 136 over a network for collaborative processing, whereby changes to the screen of the local computer are to be reflected on the screen of the remote computer. A hook routine 110 is used to intercept requests to update the screen of the local computer, and the area of the screen to be updated is determined from the request. Another routine then obtains the bit map for the area of the screen which has been updated, and only this bit map is transmitted to the remote computer, rather than one corresponding to the whole screen.

Abstract: A computer workstation runs an application 12 which generates data for transmission over a network. The workstation includes a communications subsystem 14 which is responsible for actually sending data generated by the application onto the network. The application therefore passes data 22 for sending to the communications subsystem, along with the identification 24 of the channel over which that data is to be sent, and compression information 26. In a first embodiment the communications subsystem contains a variety of compression routines 40, and the compression information indicates which of these routines is most appropriate for the data in question. In a second embodiment, the compression information is a call-back function 92, whereby the communications subsystem can call back to the application program to perform the compression itself.