Accurate time or clock synchronization and frequency accuracy/stability are required when multiple devices render related content. Examples of such related content include, but are not limited to, audio and video (lip-synchronization); audio and audio (networked stereo speakers); and so forth.
But sometimes accurate time or clock synchronization and frequency stability across the entire network is neither present nor necessary, for example when only a part of the network supports an accurate time protocol and the stream source needs only an estimate of the current time so that it can, for example, tell the speakers (which are accurately synchronized) to start the stream. Network technologies may include, but are not limited to, Ethernet (Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard), Wireless (IEEE 802.11 standard) and Powerline (HomePlug AV (HPAV)).