The H.324 standard is new. It provides a foundation for interoperability and high quality video, voice, and data-based phone calls, and was recently adopted by the ITU. The H.324 standard specifies a common method for simultaneously sharing video, voice, and data over high-speed modem connections.
It is the first standard to specify interoperability over a single analog line. This means that the next generation of videophone products will be able to talk to one another and provide a foundation for market growth.
The H.324 standard uses a normal 28,800 b/s modem connection between callers. This is the same type of modem connection that is used today to connect PC-users to the Internet and other online services. Once a modem connection has been established, the H.324 standard specifies how digital video and voice compression technologies are used to convert sounds and facial expressions into a digital signal.
The H.324 standard defines how these signals are compressed to fit within the data rate allowed by analog phone lines and modem connections. The data rate allowed by modems is up to a maximum of 28,800 b/s. Voice is compressed down to a rate of around 6,000 b/s. The video picture is also compressed, and uses the rest of the bandwidth allowed by the modem connection.
The H.324 standard and its capability will be added to new phones in a variety of shapes and sizes. The following are examples of videophone products consumers will see over the next couple of years as a result of this standard:
■ Stand-alone videophone – This device will appear like a wall telephone, but with a camera mounted on top and an LCD display.
■ TV-based videophone – This videophone will look like a cable set-top box with a built-in camera and it will sit on top of a television. The TV will be used for displaying a videophone image.
■ PC-Based Videophone – There will also be H.324 videophone software applications for PCs. Software-based videophones will use color monitors to display images, and 28,800 b/s modems to connect to other videophones.
Software-based videophones will take advantage of the processor’s performance in compressing and decompressing audio and video signals. There will also be PC-based videophone products available that will run on slower PC’s.
These products will be more expensive than software-based videophones. They will use addin boards with advanced digital signal processors (DSPs) to compress audio and video and to perform modem functions.
Although video quality is much better than in earlier versions of analog videophone products, H.324 products do not offer “TV” quality. The audio (voice) will sound like a normal phone call, but the video picture will vary depending on screen size.
For example, if an image is displayed inside a 176 x 132 pixel window on both ends of a videophone connection, the video picture can be delivered up to 15 frames per second. This rate is roughly half that of the frame rate used for television.
But, while the H.324 standard states that videophone products can deliver up to 15 frames per second, the actual frame rate for a videophone will vary depending on the size of the video window selected and the movement of participants during a video phone call.
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