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Appendix D: Troubleshooting
Video image of the HMX receiver has horizontal lines across the
screen
When video is transmitted by extenders, the various lines of each screen are divided up and
transmitted as separate data packets. If the reception of those packets is disturbed, blinding
occurs, which means lines are displayed in place of the missing video data packets.
There are several possible causes for the loss of data packets:
•
Incorrect switch configuration. The problem could be caused by multicast flooding, which
causes unnecessary network traffic. IGMP snooping is designed to combat this, however,
there can be numerous causes of the flooding.
•
Speed/memory bandwidth issues within one or more switches. The speed and capabilities of
different switch models varies greatly. If a switch cannot maintain pace with the quantity of
data being sent through it, it inevitably starts dropping packets.
•
One or more HMX units may output jumbo frames due to the video resolution (2048 horizontal
pixels) being used. If jumbo frames are output by an HMX unit, but the network switches are
configured to use jumbo frames, the switches attempt to break the large packets into standard
packets. This process introduces a certain latency and could cause dropped packets.
Solutions
•
Ensure that IGMP snooping is enabled on all switches within the subnet.
•
Where each HMX unit is connected as the sole device on a port connection to a switch, enable
IGMP Fast-Leave (also called Immediate Leave) to reduce unnecessary processing on each
switch.
•
Check the video resolutions provided to the HMX transmitters. If resolutions using 2048
horizontal pixels are unavoidable, ensure the Jumbo frames are enabled on all switches.
•
Check the forwarding mode on the switches. If Store and forward is being used, try selecting
Cut-through to reduce latency on lesser switch designs.
•
Ensure that one device within the subnet is correctly configured as an IGMP Querier. This is
usually a layer three switch or multicast router.
•
Try adjusting the transmitter settings on each HMX to make the output data stream as efficient
as possible.
Appendices.....
37
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