Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

The H series recommendations are ITU standards that define audiovisual and multimedia systems. There are too many recommendations in the series to list here. A synopsis is given below. Refer to the ITU Web site listed on the related entries page for a complete list and description of each recommendation. H.323 is perhaps the most important H series recommendation. It describes voice and video (multimedia) over packets-switched networks (the Internet). See "H.323 Multimedia Conferencing Standard" for more information.

• H.100 to H.140    Visual telephone system, videoconferencing, codecs
• H.200    Framework for recommendations for audiovisual services
• H.221 to H.226    Transmission multiplexing and synchronization in audiovisual services
• H.230 to H.235    Systems aspects of audiovisual services (frame synchronization controls, multipoint controls, confidentiality systems, encryption, security)
• H.242 to H.247            Communication procedures for audiovisual services (communication setup, multimedia control protocols, broadband audiovisual)
• H,261 to H.263    Coding of moving video for audiovisual services (video codecs)
• H.281    Camera control protocol for videoconferencing
• H.310 to H.332    Systems and terminal equipment for audiovisual services (packet-based multimedia)