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AXIS 212 PTZ - Video Streams
13
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 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 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 network. This means that
the video stream goes independently to each user, and each user gets their own stream. A benefit of unicast
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ing 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.
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.
Unicasting should be used for video-on-demand broadcasting. However, if more and more unicast clients
connect simultaneously, the server will at some point become overloaded. There is also a maximum of 20
simultaneous viewers to be considered.
RTP/RTSP
This unicast method is RTP tunneled over RTSP. This can be used to exploit the fact that it is relatively simple to
configure firewalls to allow RTSP traffic.
RTP/RTSP/HTTP or RTP/RTSP/HTTPS
These two methods can also be used to traverse firewalls. Firewalls are commonly configured to allow the HTTP
protocol, thus allowing RTP to be tunneled.