Why are impairment Flow Filters so important
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To ensure that the correct effect is seen on Time Error at the DUT it is important that the impairments In a forward direction this is to the Sync message and in the reverse direction this is to the Delay Request To ensure that PTP packets containing these messages are identified correctly it is necessary Once a match is found the appropriate next impairment step is applied to the transmission/receipt of that packet. For example applying a G.8261 impairment pattern to Sync messages would result in each delay value being applied
etc To ensure only Sync messages have the pattern applied you define a Flow Filter. If no Flow Filter is defined then the delay pattern would be applied to any message being sent in the forward direction. So taking the above example with Delay Responses being sent between Sync messages you would see the effect
etc The effect on the DUT downstream is that the delay pattern would be diluted since it would not be applied to only Syncs resulting in a different Time Error behaviour to that intended by the standard. |
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