User guide

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Appendix B
Troubleshooting
Problem: The video image of the ALIF receiver shows horizontal lines
across the screen.
This issue is known as Blinding because the resulting video image looks as
though you’re viewing it through a venetian blind.
When video is transmitted by ALIF units, the various lines of each screen are
divided up and transmitted as separate data packets. If the reception of those
packets is disturbed, then blinding is caused. The lines are displayed in place of
the missing video data packets.
There are several possible causes for the loss of data packets:
• Incorrectswitchconguration.Theproblemcouldbecausedbymulticast
ooding,whichcausesunnecessarynetworktrafc.ThisiswhatIGMP
snooping is designed to combat, 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, then it will
inevitably start dropping packets.
• OneormoreALIFunitsmaybeoutputtingJumboframesduetothevideo
resolution(2048horizontalpixels)beingused.Ifjumboframesareoutput
by an ALIF unit, but the network switches have not been configured to use
jumbo frames, the switches will attempt to break the large packets down
into standard packets. This process introduces a certain latency and could be
a cause for dropped packets.
• OneormoreALIFunitsmaybeusinganoldrmwareversion.Firmware
versionspriortov2.1exhibitedanissuewiththetimingofIGMPjoinand
leave commands that caused multicast flooding in certain configurations.
Remedies:
• EnsurethatIGMP snooping is enabled on all switches within the subnet.
• WhereeachALIFunitisconnectedasthesoledeviceonaportconnection
to a switch, enable IGMP Fast-Leave (aka Immediate Leave) to reduce
unnecessary processing on each switch.
• Checkthevideoresolution(s)beingfedintotheALIFtransmitters.If
resolutionsusing2048horizontalpixelsareunavoidablethenensurethat
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 as this mode causes reduced latency on
lesser switch designs.
• EnsurethatonedevicewithinthesubnetiscorrectlyconguredasanIGMP
Querier, usually a layer 3 switch or multicast router.
• EnsurethatthermwareineveryALIFunitisversion2.1orgreater.
• TryadjustingthetransmittersettingsoneachALIFtomaketheoutputdata
stream as efficient as possible. See ALIF transmitter video settings for
details.
continued