Motion Picture Experts Group (MPEG) open(ISO/IEC) standards that can be
used for streaming.
|
MPEG1 |
originally developed for VHS quality video on CD-ROM in 1988 and has
its optimal bit rate at about 1.5Mb/s for quarter screen TV (352x240) at 30 frames/sec.
MPEG-1 is mainly considered as a storage format, however it does offer
excellent streaming quality for the bit-rate it supports. |
|
MPEG2 |
was ratified in 1996. It was designed for use in digital TV
broadcasting and is best known for DVD encoding. Its target bit-rate is
between 4 and 9Mb/sec but it can be used in HDTV for resolutions up to
1920x1080 pixels at 30 frames/sec which will witness average bit rates up to
80 Mb/sec. As an Internet streaming technology it is probably not useful as
it uses bit rates higher than those to which almost everyone has access. |
|
MPEG4 |
was ratified in 1999 and is a new standard specifically developed to
address Web and mobile delivery. Its optimal bit rate is between 385 to 768 Kb/sec.
There is still active work continuing on this standard but a number of groups
are putting some heavy research and development efforts behind making MPEG4
the standard on the Internet. Codecs are currently available from Microsoft
and Apple (Quicktime) but exciting developments also from organisations like
Ligos Technology [URL: |
|
MPEG-7 |
(Multimedia Content Description Interface) is scheduled for release in
July 2001 |
|
MPEG-21 |
Work in progress… (Multimedia Framework) |
Motion Picture Experts Group (MPEG)
URL: http://www.cselt.it/mpeg/
Real Networks URL: http://www.real.com/
Quicktime URL:
Quicktime server is supported natively in MAC OS. The open source Darwin Streaming
Server
[http://www.opensource.apple.com/projects/streaming] is available for
other platforms and is free.
Microsoft Windows Media
URL:
Streaming availability on the global Internet should ideally mean a server
ready to stream content to any clients who have an interest in receiving it.
Unfortunately the demand and availability of media rich content has lead to a
breakdown of the traditional client server model. Single servers streaming
content to diverse groups of clients distributed across the Internet are
ineffective in terms of both server load and network congestion.
Over the last couple of years strategies have evolved in the commercial sector
to address these problems. Content Delivery Networks (CDNs) are an attempt to
introduce a coherent approach to building an infrastructure of caching proxies,
mirror servers and proxy accelerators to enable a more efficient and speedier
delivery of streamed content to end users. The ultimate goal is to replicate
content and bring it closer to the end user in a transparent fashion. In this
way the user sees no URI changes and has no knowledge (nor interest) in the
actual source of the content.
There are several commercial CDNs already offering these services. Probably
best known is Akamai [URL: http://www.akamai.com/
iBeam [URL: http://www.ibeam.com/] use
their MaxCaster media serving system located in points-of- presence around the
world. They use proprietary software and satellite networks to push content
through their network. They claim more than 500,000 simultaneous streams now
and will be capable of serving millions of streams in the future. Edgix [URL: http://www.edgix.com/] use their
Edge Delivery Platform which includes edgeMedia, edgeNews, and edgeStream to
ensure high performance delivery of content to end users.
Although the above are commercial ventures, the notion and requirement for the
CDN model has been appreciated generally. Over the last 12 months work has been
carried out within The United
Kingdom Education & Research Networking Association (UKERNA) [URL: http://www.ukerna.ac.uk/ukerna.html]
to look at providing a similar distributed resource for delivering streamed
content within UK academia. The recent upgrade to JANET (SuperJANET4 [URL: http://www.superjanet4.net/]),
providing 2.5Gbps backbone links increasing to 10Gbps in the next two years,
provides a huge leap in bandwidth availability. This offers excellent
opportunities to experiment with streaming media but is also cause for concern
as without proper management even large bandwidths like this can be swamped.
UKERNA intend to pilot an implementation of a content management system using
the JANET core network. Content will be replicated at the edge of the (core)
network and clients automatically directed to their nearest edge node. In this
way core network resources are far more efficiently managed than in a
centralised server model, and the end user should benefit from better and
faster access to the resources they require.
SuperJANET4 new backbone contains eight Core Points-of-Presence (C-PoPs)
geographically located throughout the UK [URL: http://www.superjanet4.net/colocation//].
Here bandwidth and switching converge and offer the capacity to accommodate
additional services and opportunities above pure transmission and routing.
QoS Forum URL: http://www.qosforum.com/
Others interesting information can be retrieved at:
|
A.T.
Campbell, G. Coulson e M. E. Kounavis, "Managing Complexity: Middleware
Explained", IEEE IT Pro September 1999 |
|
A. Fuggetta, G.P. Picco, G. Vigna,
"Understanding Code Mobility", Politecnico di Milano, Politecnico
di Torino, Italy, 1997 |
|
"The
Need for QoS", white Paper, Luglio 1999, disponibile on line presso http://www.qosforum.com/ |
|
J.Postel, "Internet Protocol - DARPA
Internet program portocol specification", RFC791 |
|
J.W.
Stamas, DK Gifford, "Remote Evaluation", ACM Transaction on
Programming Languages and Systems, Vol.12 No. 4, October 1990 pp 537-565 |
|
J.
Viteck, G. Tschundin, "Mobile Object Systems: Towards the Programmable
Internet", Vol 1222 of Lecture Notes on Computer Science,
Springer-Verlag, April 1997 |
|
J.
Waldo, G. Wyabt, A. Wollrath, S. Kendall, "A note on Distribuited
Compyting", in J. Vitek, C. Tschudin Editors "Mobile Object Systems
Towards the Programmable Internet" LNCS 1222 Springer-Verlag, 1997 |
|
Xipen
Xiao and Lionel M. Ni., "Internet WoS: Abig Picture", IEEE Network,
March/April 1999 |