ADDER AdderLink ALIF1000T User Manual page 30

Spanning Tree Protocol (STP)
In order to build a robust network, it is necessary
to include certain levels of redundancy within the
interconnections between switches. This will help to
ensure that a failure of one link does not lead to a
complete failure of the whole network.
The danger of multiple links is that data packets,
especially multicast packets, become involved in
continual loops as neighbouring switches use the
duplicated links to send and resend them to each
other.
To prevent such bridging loops from occurring, the
Spanning Tree Protocol (STP), operating at
2, is used within each switch. STP encourages all
switches to communicate and learn about each
other. It prevents bridging loops by blocking newly
discovered links until it can discover the nature of
the link: is it a new host or a new switch?
The problem with this is that the discovery process
can take up to 50 seconds before the block is lifted,
causing problematic timeouts.
The answer to this issue is to enable the portfast
variable for all host links on a switch. This will
cause any new connection to go immediately into
forwarding mode. However, take particular care
not to enable portfast on any switch to switch
connections as this will result in bridging loops.
ALIF transmitter video settings
Each ALIF transmitter includes controls to help you
customise how video data is transmitted. When
configured correctly for the application, these can
help to increase data efficiency.
Background Refresh
The transmitter sends portions of the video image
only when they change. In order to give the best
user experience, the transmitter also sends the
whole video image, at a lower frame rate, in the
background. The Background Refresh parameter
controls the rate at which this background image
layer
is sent. The default value is 'every 32 frames',
meaning that a full frame is sent in the background
every 32 frames. Reducing this to 'every 64 frames'
or more will reduce the amount of bandwidth
that the transmitter consumes. On a high-traffic
network this parameter should be reduced in this
way to improve overall system performance.
Colour Depth
This parameter determines the number of bits
required to define the colour of every pixel.
The maximum (and default) value is '24 bit'. By
reducing the value you can significantly reduce
bandwidth consumption, at the cost of video colour
reproduction.
Peak Bandwidth Limiter
The transmitter will employ a 'best effort' strategy
in sending video and other data over the IP
network. This means it will use as much of the
available network bandwidth as necessary to
achieve optimal data quality, although typically
the transmitter will use considerably less than the
maximum available.
In order to prevent the transmitter from 'hogging'
too much of the network capacity, you can reduce
this setting to place a tighter limit on the maximum
bandwidth permissible to the transmitter.
Frame Skipping
Frame Skipping involves 'missing out' video frames
between those captured by the transmitter. For
video sources that update only infrequently or
for those that update very frequently but where
high fidelity is not required, frame skipping is a
good strategy for reducing the overall bandwidth
consumed by the system.
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