Paragon-X: Why do I need to set the Capture Flow Filters when performing a PTP measurement in Master/Slave Emulation
Why are Flow Filters so important
Time Error measurements are dependent upon capturing all of the relevant PTP message types
* Sync, Follow Up , Delay Request and Delay Response
To ensure that PTP packets containing these messages are captured correctly it is necessary
to perform enough of a deep packet inspection on received packets to determine that a received
packet contains a PTP payload with one of the required message types.
Once a match is found the PTP payload is extracted from a copy of the received packet and this
along with the associated receive timestamp is passed to the higher order application code for
processing.
If no Flow filters are defined then all packets are treated as being a match and the 'PTP payload' bytes
at the PTP offset defined by the encapsulation are passed up to the Application code.
This can result in capturing non-PTP traffic which is then interpreted as if it is PTP traffic. Since
the Application code assumes a PTP payload it will attempt to parse this data as if it were PTP. This
can result in false identification of PTP message type.
For example an ESMC Slow Protocol message will be identified as a Peer Delay Response Follow-up message
due to the fact that at offset 00 is 0x0A
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