PDF of this tutorialWhile circuit-based videoconferencing streams (including motion JPEG running at rates around 10 Mbps) can be handled by standard circuit emulation using AAL–1, the ATM Forum has specified the use of VBR–RT VCs using AAL–5 for MPEG2 on ATM for video-on-demand applications, as this approach makes better use of networking resources.
MPEG is a set of standards addressing coding of video and surround-sound audio signals and synchronization of video and audio signals during the playback of MPEG data. It runs in the 2 Mbps to 15 Mbps range (with bursts above these rates) corresponding to VCR and broadcast quality respectively. The initial MPEG standard (MPEG1) was targeted at VHS–quality video and audio. MPEG2 targets applications requiring broadcast-quality video and audio and HDTV. MPEG2 coding can result in one of the following two modes:
- program streams—variable-length packets that carry a single program or multiple programs with a common time base
- transport streams—188-byte packets that contain multiple programs (for examples, see Figure 6).
Figure 6. Transport Streams
In both cases, time stamps are inserted into MPEG2 packets during the encoding and multiplexing process. MPEG2 assumes a constant-delay model across the network, thus allowing the decoder to exactly follow the original encoder source clock. Due to the cost of coding, MPEG2 is primarily used in a non-interactive broadcast mode as would be the case for a point-to-multipoint broadcast in residential video on demand applications and in a business TV application for training or employee communications.
