User guide

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35
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
flooding, which causes unnecessary network traffic. 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 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 Alter ALIF transmitter video settings if
necessary for details.
Problem: The audio output of the ALIF receiver sounds like a scratched
record.
This issue is called Audio crackle and is a symptom of the same problem that
produces blinding (see left). The issue is related to missing data packets.
Remedies:
As per blinding discussed previously.
continued