Adventures in H.323 Videoconference Streaming and Recording

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Adventures in H.323 Videoconference Streaming and
Recording

• John Langkals
• Technology Engineer
• OARnet
• OARnet H.323 Training
• May 2002

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What is Video Streaming?

• Streaming video is taking a large media file
  that has been requested, and transmitting small,
  continuous amounts of that file over the network
  or Internet to a software player.

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Streaming Server
Client software player
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The Magic of Streaming Video

• The media streamed can be a live or a recorded
  event.
• The user can start viewing the media without
  waiting until the end of transmission.
• Streaming video can be archived and replayed
  anytime by anyone anywhere in the world.

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Buffering

• Buffering is when the streaming media enters the
  users computer at a faster rate than can be
  played.
• A small amount of the media is downloaded, and
  then while that initial portion is playing, the
  next part of the media is downloaded and stored
  in memory.
• Buffering allows for network hiccups.

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What about Unicast and Multicast?

• Unicasting creates a stream from the server for
  each client request.
• Multicasting is the technology that replicates
  packets at the router level, easing the load on
  the streaming server as well as the internal
  network.

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Unicast Individual Requests
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Unicast

• The traditional method for transmitting media
  over the internet is unicast.
• This can be quite network intensive when multiple
  streams are requested.
• Its VOD. It has no definite start or stop time.

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Multicast Reflecting
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Multicasting 

• When a request for a stream is made, the server
  sends out a single multicast stream to the
  router.
• The router recognizes it as a multicast stream
  and then duplicates the stream for each
  additional client request.
• Its comparable to a television broadcast. Its
  a shared connection.

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What about Webcasting?

• Webcasting describes a unicast Internet
  broadcast.
• Actually webcasting is a marketing term that has
  no technical meaning.

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How on earth does the Internet deliver Streaming
Media?

• Streaming media is one of the major technologies
  pushing the evolution of the Internet.
• The network requirements for streaming video and
  audio are radically different than static text.
•  TCP/IP, UDP/IP, and HTTP 

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TCP/IP
TCP/IP and HTTP protocols are guarantee-based
and not time-based protocols. Both perform
poorly when streaming a time dependent media such
as audio and video. Web Pages and FTP
download More Complex
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UDP/IP
User Datagram Protocol was developed to solve the
issue of time-based delivery of the network data.
Streaming Media Simpler
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Network protocols to handle the transfer of video
and audio

• UDP
• User Datagram Protocol
• RTP
• Real-time Transfer Protocol
• RTSP
• Real Time Streaming Protocol

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UDP/IP vs TCP/IP

• TCP and UDP are two most commonly used
  transport protocols on the Internet.
• TCP provides a connection-oriented and reliable
  flow between two hosts.
• UDP provides a connectionless but unreliable
  datagram service over the network.

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What does UDP do?

• The UDP protocol is designed to transfer packets
  in time, and not worry about resending lost
  packets.
• Effective streaming requires that the data arrive
  in a timely and orderly fashion.
•  
• If the client had to wait for each lost packet to
  be present, there would be many pauses in the
  video and ultimately an unsatisfactory
  experience.

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RTP

• Real-time Transport Protocol is the transport
  protocol for real-time data.
• RTP is the mechanism for packaging the video
  audio data.
• RTP is usually transported via UDP but can be
  transported over TCP.

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What about RTP?

• Packets sent on the Internet have unpredictable
  delay and jitter.
• RTP provides time stamping and sequence numbering
  to handle the timing issues in real-time data
  transport.

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RTSP

• RTSP provides "VCR-style" remote control
  functionality for audio and video streams, with
  functions such as pause, fast-forward, and
  rewind.
• RTSP is a control protocol that initiates and
  directs delivery of streaming multimedia data
  from media servers the actual data delivery is
  done by RTP.
• RTSP is carried over TCP because it is a reliable
  transport mechanism and the control messages must
  successfully make it to the server.

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More on RTSP

• RTSP aims to provide the same services on
  streamed audio and video just as HTTP does for
  text and graphics.
• It uses URLs like those in HTTP.
• While HTTP is a stateless protocol, an RTSP
  server has to maintain session states in order to
  correlate RTSP requests with a stream.

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Recap

• RTSP and RTP are application level packaging.
• TCP and UDP are network protocols that RTSP, RTP,
  and HTTP are carried in.
• Application level
• RTSP messaging (VCR like controls)
• RTP transports video and audio data
• Network Protocol
• TCP reliable/guaranteed
• UDPunreliable/not guaranteed

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H.323 and Video Streaming

• H.323 is all about negotiating exchange of
  multimedia data and it describes video
  compression techniques H.261 and H.263.
• When we rebroadcast it, the H.323 signaling is
  stripped off and take the raw and video data and
  rewrap it as WM, QT, or RealOne.
• The H.323 stack is not involved with player
  requests, that is part of the secret sauce.

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Digitally Recording H.323 VC

• We record the H.323 transmission digitally bit by
  bit with no analog or baseband signals involved.
• As the encoding is handled at the endpoint and
  not within the streaming unit, the streaming
  hardware can be located anywhere. It does not
  need to be at the site of the event.
• There is no encoding or decoding of the video.
  This results in low overhead less processor
  intensive and less delay.

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Any Questions?

• Videoconference recording
• and streaming demonstration
• using the Starbak Communications Torrent CE

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User Interface

• Stream recording and replay is done over a web
  browser using a free software player.
• Password authentication
• Chat feature, slide function and web portal
  capabilities.

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