Axis Communications 221 - Manual (Page 12)

12 AXIS 221 - 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 (Realtime Transport Protocol) 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 alterna-
tive 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 e.g. 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 net-
work. 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 simul-
taneously 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 efficient 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 e.g. the Internet.