H261 is the most widely used international video compression standard for video conferencing. This ITU (was CCITT) standard describes the video coding and decoding methods for the moving picture component of a audiovisual service at the rates of p * 64 Kbps where p is in the range of 1 to 30. The standard targets and is really suitable for applications using circuit switched networks as their transmission channels. This is understandable as ISDN with both basic and primary rate access was the communication channel considered within the framework of the standard.
H.261 is usually used in conjunction with other control and framing standards such as H221, H230 H242 and H320, of which more later.