Following are the primary standards used with videoconferencing. See videoconferencing.Videophone DirectoryH.350 is the ITU standard for a videophone directory. See H.350.T1 and Dial-Up Networks (H.320 and H.324)H.320 is the ITU standard for dial-up ISDN, fractional T1 and Switched 56 services. H.324 is used with regular phone lines and analog modems. See H.320 and H.324.IP Networks (H.323 and SIP)H.323 is the ITU standard for voice and video over packet networks, which means IP LANs and the public Internet. SIP is the IETF standard for voice and video over IP. Some videoconferencing systems are able to handle H.323 and SIP clients simultaneously. See H.323 and SIP.Compression (H.263 and H.264)The primary ITU codecs for compressing video are H.263 and H.264, the latter halving the bandwidth requirement of the former. See H.263 and H.264.Showing Data (H.239 and T.120)The H.239 standard splits bandwidth between conferencing video and a second video source. It enables participants to connect their PCs to the second video stream and share their computer screens with everyone in the conference.T.120 is the ITU standard for whiteboards, application sharing and application viewing, all of which can be used with or without videoconferencing. However, T.120 collaboration with videoconferencing never took off and gave way to proprietary standards for simply splitting the bandwidth and showing a second data channel. Those methods evolved into H.239. See H.239, T.120, whiteboard, application sharing, videoconferencing and telepresence.