H.320 - technical definition

Also known as Px64.The ITU-T umbrella standard for videoconferencing and multimedia communications over narrowband ISDN (N-ISDN) bearer (B) channels at bit rates from 64 kbps to 1.920 Mbps, in increments of 64 kbps.Video compression makes use of codecs defined in H.261.Video formats include Common Intermediate Format (CIF), which is optional, and Quarter-CIF (QCIF), which is mandatory in compliant codecs. CIF supports resolution of 352 × 288 pixels, and QCIF supports resolution of 176 × 144 pixels, which is exactly 1 / 4 the resolution of CIF. Frame rates are 30 frames per second (fps), or lower. Audio coding and compression recommendations include G.711, which is pulse code modulation (PCM) at 64 kbps. G.722 is high fidelity adaptive differential pulse code modulation (ADPCM) transmitting up to a 7 kHz range and compressing voice at 48/56/64 kbps. G.728 specifies low delay code-excited linear prediction (LD-CELP) running in the 3 kHz range and compressing voice at 16 kbps. The balance of the specification (H.221, H.230, and H.242) addresses techniques for call setup and teardown, data framing and multiplexing, and various other operational and administrative functions. See also ADPCM, B channel, CIF, codec, frame, frame rate, fps, G.711, G.722, G.728, H.221, H.230, H.242, H Series, ITU-T, LD-CELP, multimedia, N-ISDN, PCM, pixel, QCIF, resolution, video, and videoconference. See Table H-1 for a listing of ITU-T Recommendations related to H.320.

Table H-1: H.320 Related Standards Recommendations

ITU-T Recommendation	Description
G.711	Pulse Code Modulation (PCM) voice coding at 64 kbps.
G.722	Adaptive Differential Pulse Code Modulation (ADPCM) voice coding and compression of high-fidelity 7 kHz voice at 64/56/48 kbps.
G.723	Dual-rate speech coder at 5.3 and 6.3 kbps for multimedia communications.
G.728	Low-Delay Code Excited Linear Prediction (LD-CELP) coding and compression of 3.3 kHz voice at 16 kbps.
G.729	Conjugate-Structure Algebraic-Code-Excited Linear-Prediction (CS-CELP) voice coding and compression at 8 kbps.
H.221	Frame Structure for channel of 64­1920 kbps in audiovisual teleservices.
H.223	Multiplexing protocol for low bit-rate multimedia communication. Annexes address mobile communications over low, moderate, and highly error-prone channels.
H.225	Call signaling protocols and media stream packetization for packet-based multimedia systems.
H.230	Frame synchronous control and indication signals for audiovisual systems.
H.242	System for establishing communications between audiovisual terminals using digital channels up to 2 Mbps. Addresses call setup and teardown, in-band signaling and control, and channel management.
H.245	Call control procedures for multimedia communications.
H.261	Video codec for audiovisual services at px64 kbps.
H.263	Video coding for low bit-rate communication at rates less than 64 kbps.
T.120	Multipoint transport of multimedia data.