By Mukta L. Kar and Bill Kostka, Cable Television Laboratories, Inc., Majid Chelehmal, Terayon Communication Systems, and Munsi Haque, Philips Semiconductor
With the rapid progress in science and
technology, more and more applications
involving audio and video streams are
emerging. The MPEG-2 compression standard,
coupled with advances in digital modulation,
has already made an impact in the broadcast
industry by increasing the number of channels
and viewing quality. However, consumers have
limited choice―purchasing or renting CDs and
DVDs from a limited stock or selecting from
limited movie and music offerings.
Digital technology has advanced in a
number of fronts, including the transport of
data over public or private networks. High-
speed data can be transported in a variety of
ways―unicast, multicast, or even broadcast
using various transport protocols. Digital
information, such as audio, video, text,
graphics, etc., differs only in the size of data.
For example, digitized video is much larger
than digitized audio. Advances in fiber
technology have increased the capacity of
both public and private networks to the point
that audio and video streaming is becoming a
reality. CableLabs, and other research institutes,
have found that there are a few obstacles to
overcome before broadcast-quality video
streaming is possible over public networks.
When those issues are resolved, electronic
search engines will be able to find the desired
content in archives located anywhere in the
world. Consumers will be able to enjoy their
content choices with a click of a button.
One major issue is the transport
mechanism (protocol) for real-time,
uninterrupted flow of digital audio, video,
graphics, etc. MPEG-2 transport protocol
and IP-based Real-time Transport Protocol
(RTP) are currently the two leading protocols
used for the delivery of digital content in
real-time. This paper will analyze these two
protocols in detail, and will present
comparative studies for streaming
technology. This technology is not mature;
e.g., streaming in IP networks is implemented
as part of transmission application layer
protocols, where the unreliable user
datagram protocol (UDP) is used mostly at
the transport layer. To alleviate packet loss,
RTP with quality-of-service (QOS) routing is
considered for improved services in IP
networks.
Issues and obstacles for streaming audio-
visual content, particularly over the public
networks, will be addressed in this paper.
Research activities addressing some of the
problems also will be discussed. Finally,
content streaming based on MPEG-4, the
recently completed multimedia standard, also
will be discussed.