Appendix B. Troubleshooting - Black Box ACR1000A-CTL-24 Manual

iPATH Agility Controller

Appendix B. Troubleshooting

Problem: The video image of the Agility 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 Agility 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 configuration. 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 Agility units may be outputting Jumbo frames due to the video resolution (2048 horizontal pixels) being used. If
jumbo frames are output by a Agility 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 Agility units may be using an old firmware 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 Agility 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 Agility 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 configured as an IGMP Querier, usually a layer 3 switch or multicast router.
• Ensure that the firmware in every Agility unit is version 3.3 or greater.
• Try adjusting the transmitter settings on each Agility to make the output data stream as efficient as possible.
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