When application sharing, there must be a common denominator between platforms in the conference so that they can all effectively communicate and understand the data that is received. The ITU initially developed and approved the T.120 data conferencing standard.

T.120 allows data sharing and true collaboration to the extent that another endpoint could actually take control of the shared application. Most vendors offered a T.120 solutions by integrating NetMeeting™ either directly into their PC based systems or indirectly with a PC link to their non-PC based Settop systems. However, T.120 has now given way to the new H.239 Dual Video standard.

The H.239 standard defines how additional media channels are used and managed by Video Conferencing systems. H.239 introduces the concept of 'data-showing', whereby the PC desktop graphics is converted into a separate media stream and transmitted in along with the main video stream. The new common denominator is the media stream, so it does not matter if the endpoint is PC or settop based. Endpoints that support H.239 will receive the dual streams and display the desktop graphics and far-end video in separate windows. Endpoints that don't support H.239 will display the graphics instead of the far-end video in one window, which may not be full screen!

Although H.239 is new, the major vendors have implement it in their latest product releases; Emblaze-VCON's vPoint HD has HD DualStream™, Tandberg have DuoVideo™, Polycom' have People+Content™ on PVX and the VSX series whilst Sony have H.239 support on their products.