Axis Communications 241S Manuel D’Utilisation

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.

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, so that there is no video 

traffic on the network until a client connects and requests the stream. 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.