Time Stamp Features

Napatech Link™ Capture Software Features
Platform
Napatech SmartNIC
Content Type
Feature Description
Capture Software Version
Link™ Capture Software 12.5

Time stamp relative to frame duration

Received frames are time-stamped according to the internal SmartNIC time either when the first byte is received or when the last byte is received depending on the TimestampMethod configuration parameter in the ntservice.ini file (see DN-0449). This setting also determines if the first or the last byte of a frame is transmitted according to the time stamp.
Note: Start-of-frame time-stamping does not apply to NT40E3-4-PTP SmartNICs running on the capture/replay image, to NT40A01 SmartNICs running on the 4 × 10/1 Gbit/s SLB image nor to the Intel® Programmable Acceleration Card with Intel® Arria® 10 GX FPGA.
Note: Using different settings of TimestampMethod for capturing data and later for transmitting the same data, will result in inaccuracies.

Size and location of time stamp

The time stamp information is provided in the packet descriptor of every frame. For the standard descriptor it can be retrieved using the NT_NET_GET_PKT_TIMESTAMP macro (see DN-0449). The size of the time stamp field is 64 bits.

Time stamp formats

There are four time stamp formats with different start times:

  • Native UNIX format based on a 10 ns unit, with a 64-bit unit counter. The start time is January 1st 1970.
  • Native UNIX ns format based on a 1 ns unit, with a 64-bit unit counter. The start time is January 1st 1970.
    Note: Native UNIX ns format does not apply to NT40A01 running on the 4 × 10/1 Gbit/s SLB image.

  • PCAP-μs format based on a 1000 ns (1 μs) unit, with a 32-bit unit counter in the MSBs of the time stamp descriptor field, and a 32-bit second counter in the LSBs of the time stamp descriptor field. The start time is January 1st 1970.

  • PCAP-ns format based on a 1 ns unit, with a 32-bit unit counter in the MSBs of the time stamp descriptor field, and a 32-bit second counter in the LSBs of the time stamp descriptor field, so the time resolution is 1 ns. The start time is January 1st 1970.

Time offset value

The SmartNIC time provided from an external time source, for instance a GPS signal, can be adjusted by an offset if required. This can be used, for instance, to compensate for delays in time synchronization cables.

Data path delays

RX and TX data path delay values are available in the API to allow applications to compensate for these delays (see DN-0449).

Format limitations

The internal SmartNIC time, time offset and time stamp format are global settings for the SmartNIC, so all received frames use the same time source and format.

If the SmartNIC is time-synchronized to another SmartNIC, it is recommended that the time stamp format of the time slave SmartNIC is the same as the time stamp format in the time master SmartNIC.

If the traffic from two SmartNICs is SW-merged, the time stamp formats of the two SmartNICs must be the same.

PCAP-ns or PCAP-μs format can only be used if the PCAP packet descriptor is selected for all SmartNICs (see Restrictions on the PCAP packet descriptor).