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 |