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Understanding time stamps
346 GigaStor (23 Feb 2018) — Archive/Non-authoritative version
Probe ID(s) A comma separated list of hexadecimal characters from a
PacketPortal IV SFProbe or JMEP. Use PacketPortal System
Manager (IV SFProbe) or the SFP Programmer GUI (JMEP) to
view a list of probe IDs. A sample probe ID: 5e65eb52f633 .
Setting the probe’s time clock synchronization settings
At times your capture card drivers time clock may drift. They can be synchronized
with the system clock, if you wish. Unless you notice a reason to enable this
feature, we recommend that you do not synchronize your capture card’s time
clock.
Some Other things to consider:
♦
The capture card synchronizes itself with the system clock at when the
system starts.
♦
Generally, you are interested in relative time between packets, not the
actual time a packet was seen.
1. Do one of the following:
●
On the probe: Click the Synchronization tab .
●
In Observer: Select a probe instance, right-click and choose Administer
Selected Probe. Then click the Synchronization tab .
2. Click the Edit Schedule button.
3. Choose when and how you want the capture card’s time clock to synchronize
with the system clock and click OK .
Daylight Savings Time
Observer is not coded with a specific date in mind. Daylight Savings Time is
controlled by the operating system. When the clock rolls backwards or forwards
Observer rolls with it, with one exception: packet capture/decode.
Packet capture provides nanosecond time resolution, which none of the rest of
the product does. Because of this, packet capture does not rely on the system
clock to provide time stamps. It relies on the processor time ticks. When Observer
opens it requests the system time and the number of processor time ticks and
uses those. This allows Observer to know what date and time it is when a packet
is seen.
Because the Observer only asks the operating system for the system time when
Observer is started, packet capture does not know that the time has jumped
forward or backward. To get this to happen you need restart Observer after the
time change. It is that simple.
Supported time stamp and synchronization methods
Observer supports several different time stamp trailers in your packets. With
these, the packets can be chronologically reordered in the order they were
sent or received by a switch, router, or device, instead of the times seen by the
capture card. Time synchronization methods are also available to Observer and
the capture card for accurate and reliable timing for when packets are seen.