IE5000 Spanned Traffic Timestamping format

[c.delmas]

Hello,

I created a local SPAN session with timestamping on an IE-5000 switch. 18-bytes long trailers are added to captured frames but what is the format of these trailers?

Any hint would be nice.

[Albert Mitchell]

can you share about your intended use.  

Im looking up the format.

[c.delmas]

My first use case is to find and compare the latency, jitter and asymmetry introduced by various copper/fiber media converters.

If the timestamping accuracy is really good, this feature will greatly help to troubleshoot synchronization issues with PTP systems.

[c.delmas]

Here is are two trailer examples:

9d 8d 00 00 00 00 00 00 63 b6 8e b8 2e bb 99 3b 26 e1
9d 8d 00 00 00 00 00 00 63 b6 8e c6 10 d2 7a 76 5a 1a

I have no clue regarding the two leading bytes which are always 9d 8d no matter the packet size or input interface.

I suppose that the four bytes at offset 8 are the seconds (1st line: 1672908472) and the next four bytes the nanoseconds (1st: 784046395). The timestamp is expressed in TAI.

I can imagine that the timestamp respects the same format than PTP so the seconds may be stored on 48 bits which would include the preceding two bytes.

The last two bytes change at each packet. Maybe a checksum or sub-nanosecond part of the timestamp, like the correction field of PTP.

[Albert Mitchell · Accepted solution]

The timestamp trailer is comprised of the following fields:

• 2 bytes Identifier – fixed 0x9D8D.
• 4 bytes Metadata – Metadata field is reserved for future use.
• 6 bytes Seconds – 6 bytes is the size of seconds field in IEEE Std 1588–2008 PTP

Timestamp datatype.

• 4 bytes Nanoseconds.
• 2 bytes of CRC-16 (1+x^2+x^15+x^16 polynomial).

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      |                                                               |

     +                         Original packet                       +

      |                                                               |

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      |          0x9D8D[15:0]         |          Metadata[31:16]      |

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      |       Metadata[15:0]          |          Seconds[47:32]       |

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      |                         Seconds[31:0]                         |

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      |                       Nanoseconds[31:0]                       |

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      |           CRC-16[15:0]        |       FCS [31:16]             |

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      |         FCS [15:0]            |

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

[c.delmas]

Thank you very much!