Data Coding Protocols

Audio Compression

G.711 employs Pulse-Code Modulation (PCM) of voice frequencies from 300 Hz to 3.4 KHz at 64 Kbps.

G.722 employs Sub-Band Adaptive Differential Pulse-Code Modulation (SB-ADPCM) to provide high-fidelity speech ranging from 50 Hz to 7 KHz and compressing voice at 48/56/64 Kbps.

G.722.1 is based on Siren codecs and offers low-complexity coding at 24 and 32 Kbps for hands-free operation in systems with low frame loss.

G.722.1 Annex C (or G.722.1C) is an extension to G.722.1 which permits 14 KHz audio bandwidth at 24/32/48 Kbps.

G.728 is a codec of speech within 3.4 KHz at low bitrates (16 Kbps) using Low Delay Code-Excited Linear Prediction (LD-CELP).

Control Protocols

H.224 defines the real-time control protocol for simplex applications using the H.221 LSD, HSD and MLP channels.

H.225.0 defines the call signaling protocol and media stream packetization for packet-based multimedia communication systems.

H.235 defines the security and encryption protocols for H.323 and other H.245-based multimedia terminals.

H.245 defines the control procedures and protocol for H.323 and H.324 multimedia communication.

H.281 defines the procedures and protocol for far-end camera control (FECC) based on H.224 in H.320 calls.

H.323 Annex Q defines the procedures and protocol for far-end camera control (FECC) in H.323 calls.

H.460 defines a series of extension to H.323 including NAT and firewall traversal.

Data Compression for Dual Media Streaming

H.239
H.239 defines the rules on role management of multiple streams and additional media channels for H300-series terminals. The additional channel allows presenter to share his/her content along with the live camera video. AVer EVC series support HDMI/DVI and VGA inputs for dual display. For presentation in multipoint conferencing, the endpoint who holds the only token assigned by H.323 MCU can distribute its content to all participants.

BFCP (Binary Floor Control Protocol)
BFCP is used to coordinate the access to shared content in SIP-based video conferencing. Acquiring a floor in BFCP is equivalent to getting a token in H.239. It is highly recommended to use UDP connection instead of TCP when you share content with BFCP because TCP is found not to work well with main NAT/firewall traversal techniques.

Video Compression

H.261 is the video codec for audiovisual services such as video telephony and video conferencing at p×64 Kbps (p= 1, 2, 3… 30). It supports two image formats, Common Intermediate Format (CIF, 352×288) and Quarter CIF (QCIF, 176×144).

H.263/H.263+ is the video codec for narrow-band telecommunications channels less than 64 Kbps. It supports two mandatory image formats, CIF and QCIF, and three optional ones, Sub-QCIF (128×96), 4CIF (704×576) and 16CIF (1408×1152).

H.264/AVC (Advanced Video Coding) is the most widely used video codec in current video conferencing systems for its high quality with unprecedentedly low delay/bit-rate. It is also employed by Blu-ray Discs and online media streaming services such as YouTube, Vimeo and iTunes Store.