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AXIS 243Q Blade - Video streams
MPEG-4 protocols and communication methods
To deliver live streaming video over IP networks, various combinations of transport
protocols and broadcast methods are employed.
• RTP (Real-Time Transport Proto
col) is a protocol that allows programs to manage
the real-time transmission of multimedia data, via unicast or multicast.
• RTSP (Real-Time Streaming Protocol) serves
as a control protocol, to negotiate
which transport protocol to use for the stream. RTSP is thus used by a viewing
client to start a unicast session, see below.
• UDP (User Datagram Protocol) is a communications protocol that
offers limited
service for exchanging data in a network that uses the Internet Protocol (IP). UDP
is an alternative to the Transmission Control Protocol (TCP). The advantage of
UDP is that it is not required to deliver all data and may drop network packets
when there is network congestion. This is suitable for live video, as there is no
point in re-transmitting old information that will not be displayed anyway.
• Unicasting is communication between a single
sender and a single receiver over a
network. This means that the video stream goes independently to each user, and
each user gets their own stream. A benefit of unicasting is that if one stream fails,
it only affects one user.
• Multicast is bandwidth-conserving technology
that reduces bandwidth usage by
simultaneously delivering a single stream of information to multiple network
recipients. This technology is used primarily on delimited networks (intranets), as
each user needs an uninterrupted data flow and should not rely on network
routers.
How to stream MPEG-4
Deciding on the combination of protocols and methods to use depends on your viewing
requirements, and on the properties of your network. Setting the preferred method(s) is
done in the control applet for AMC, which is found in the Windows Control Panel. When
this has been set, AMC will test all the selected methods in the specified order, until the
first functioning one is found.
RTP+RTSP
This method (actually RTP over UDP and RTSP over TCP) should be your first consideration
for live video, especially when
it is important to always have an up-to-date video stream,
even if some images do get dropped. This can be configured as multicast or unicast.
Multicasting provides the most effic
ient usage of bandwidth, especially when there are
large numbers of clients viewing simultaneously. Note however, that a multicast broadcast
cannot pass a network router unless the router is configured to allow this. It is thus not
possible to multicast over the Internet.