AVB Media Converters

Peer Delay adjustments required when using media converters

The length of the fiber line and media converter will have an impact on propagation delay. If the link propagation delay exceeds the peer delay threshold, AVB clocking will not function correctly and ports will report AS-incapable. Both the switch and Tesira must have their peer delay threshold configured to account for the media conversion. The link propagation delay should be checked in the switch, and a peer delay value greater than the propagation delay should be entered. The peer delay values do not need to match on both ends, as long as both are greater than the propagation delay. 

The default peer delay threshold in Tesira is 1200ns. The peer delay threshold in Tesira is configurable up to 2,147,483,647 nanoseconds.

The TTP query DEVICE get ptpInfo can be used to see the measured pdelay value on each Tesira device's AVB interface. The device's current setting is shown as "neighborPropDelayThreshholdNs":1200 and the measured value over an AVB link is shown as "neighborPropDelayNs":16 where the value returned is the propagation delay in ns. If the measured value exceeds the default 1200 ns it is generally safe to use 1.5 times the measured value as the new pdelay value. This can be edited in the Device Maintenance > Network Settings > AVB Settings options for each device. 

MOTU AVB switches do not have a configurable peer delay and should not be used with fiber media converters.

Note: The use of media converters is not supported to extend Qt X controllers in the field from core switch locations beyond 100m. Qt X controllers have a fixed peer delay setting of 1200ns which is exceeded when using fiber media converters. AVB traffic will not flow if this propagation delay is exceeded.