H.324 Videophones
The ITU’s H.324 protocol, intended
for “videophones” that
use POTS (plain old telephone service)
phone lines (available in 97% of
US households). Products meeting this standard are not much
more difficult to use than a high-end phone or a VCR. The
main user-controlled
feature
being
interactive control of the tradeoff between reflesh rate
(e.g., typical range of 1 to 15 fps) and image quality.
Here is a list of features:
- Most function as a stand-alone appliance with simple
set-up, use TW or P C as monitor, remote control digital
pan/tilt/zoom.
- Control operations are through either a telephone keypad
or remote control.
- Most have an interactive on-screen display.
- The normal actual
bandwidth for such applications is low, typically
31-33 Kbps (with 28.8 or 33.6 Kbps internal "V.80" modem).
In this range, there is no way for high-quality video whenever
motion
is
occurring.
- Most use RCA video-in for remote camera,
support both NTSC and PAL formats and auto-answer features,
and have a built-in 33.6 Kbps modem.
- The maximum frame rate is 15 fps,
typically with a selectable range from about 1-15 fps.
- Cameras are CCD (1/5", 1/4", 1/3" or 1/4" CMOS).
- Typically
the number of pixels is CIF (354x288) or QCIF (176x144),
but some variation (e.g.,
480x234 also common).
- Most systems enable users to see both feeds (e.g.,
via picture-in-picture).
- Most have electronic pan/tilt/zoom (i.e., "fake" digital
zooming of the pixel base).
- Most use either active matrix TFT LCD display (typically
3.5" or 4" screens) that are integrated with
a phone, or settop systems
that use a TV monitor.
- Most employ low-delay full duplex audio with echo cancellation
(using G.723.1, a fairly aggressive
speech codec at 5.3
or 6.3
Kbps)
- Most employ the H.263 video codec.
- There are also security, privacy, multiplexing and data
control protocols.
Examples:
- MetaEye / TeleEye / TeleVyou (Leadtek)
for both TV settop and phone systems
- InfoView (InnoMedia)
- HyperVPhone 2000 (Aiptek)
- StarView StarView
- C-Station (H.324/H.320), CareStation (Motion
Media) [bought out older C-Phone]
- DV324 [was
Via-TV VC150 by 8x8
Inc, a company that supplied the embedded videophone for
most of the telehomecare products, butwhich has moved more
towards IP/SIP
solutions)]
- Beamer Videophones (Vialta)
Our past evaluation of H.324
products (e.g., see Chapter 13 in your reading material,
Tran et al) suggested that while most products are interoperable
(often with some
effort),
there
is no way
around
the choppy
nature of the transmitted video, especially if color is
desirable (32,34). For home telehealth products, a small screen
(e.g.,
3” by 5”) is often used so that pixelation
is less noticeable. Such small screens can be integrated
into standard
phones, with cameras integrated and/or connected by wireless
means.
These videophones are usually targeted towards telehomecare
applications where ease-of-use is a high priority and high-quality
video is not critical. There are a number of telehealth products
that integrate videoconferencing with vitals, with "telenerse"
and "patient" terminals that differ.
There are now products that are H.324/H.323, which makes some
sense given the emergence of cable modem / DSL service.
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