Video Server User's Manual

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.