NDI NewTek NDIHXPTZ4K, Руководство по эксплуатации

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M
ULTICAST OR
U
N ICAST
?
Multicast can seem like a bandwidth-saving miracle. Unlike NDI’s default mode (unicast), multicast does not
require a unique stream from the source to each receiver. When using unicast, each connection to the sender
reduces the bandwidth available by a similar amount.
By contrast, multicast connections do
not
add significantly to the bandwidth required as connections
multiply. You could be forgiven for wondering why anyone would ever turn this option off - yet, it is off by
default. Why?
This is because multicast requires more careful network
configuration. While you might not notice any issues in a simple
network setting; a poorly configured environment can have
serious impact on more complex networks.
• Specifically, it is essential that IGMP snooping be
enabled for each switch on the network. This lets the
device listen to traffic between other hosts, switches and
routers, and identify receiving ports using various IP
multicast streams.
•
In addition, we strongly recommend that all network
switches be of the ‘managed’ type (see the sidebar
“Managed vs. Un-managed”).
1.3.2
NETWORK SETTINGS
Controls in the Network Settings section will be familiar to anyone who has connected a computer or mobile
device to a network, and thus require little explanation.
FIGURE 15
Managed vs. Unmanaged
An un-managed (a.k.a., ‘dumb’)
network switch will cause a
multicast stream to revert to
unicast. This can have serious
ramifications.
For example, even though a device
broadcasts a multicast stream, the
un-managed switch will pass
unicast
packets to downstream
switches and clients. This can flood
parts of the network with
unnecessary traffic. It can even
slow down the rest of the network,
as upstream devices are forced to
wait for responses from the over-
saturated devices.
The net result of such a poor setup
can be likened to a self-inflicted
denial of service attack.