[Winpcap-users] Where does the Winpcap timestampcomefrom?andothers

[John Wang]

Hi Gianluca,

Thanks for your information, That's great helpful. I decide to use a
hardware local timer to record the beacon frames arrival time. After I
looked close to the CACE AirPcap Classic wireless adapter, I found there are
a AIROHA transceiver and a ZYDAS USB driver chip. Do you know where does the
Winpcap implement the incoming packets filtering?

Cheers

John

2009/5/7 Gianluca Varenni <gianluca.varenni at cacetech.com>

>
>
> ----- Original Message -----
> *From:* John Wang <locationdev at gmail.com>
> *To:* winpcap-users at winpcap.org
> *Sent:* Wednesday, May 06, 2009 6:36 AM
> *Subject:* Re: [Winpcap-users] Where does the Winpcap
> timestampcomefrom?andothers
>
> Hi,
>
> I'm a little bit confused about where exactly the arrival packets
> timestamps come from, in our first email, you said:
>
> "1. Where does the NPF get the time information to timestamp these incoming
> packet? The time information comes from a on board timer in the adapter or
> from a CPU or similar computer clock?
> --GV--
> From the computer clock when the packet gets delivered to WinPcap."
>
> I think that means the timestamps come from computer timer, like CPU timer.
> But in you last email, you said:
>
> "The only way to obtain that is to have some device that timestamps
> packets in hardware. And even in that case, most of the times the timestamps
> have microsecond precision (this is what we have with the AirPcap adapters
> in hardware)."
>
> That sounds like, the AirPcap adapter has a timer build in it, and the
> arrival packets timestamps come from this build in timer.
>
> So I want to get the confirmation from you, whether the arrival packets are
> timestamped by the computer timer or the AirPcap adapter build in timer.
>
> In the case of the AirPcap adapters, which are *custom* capture devices, we
> provide two timestamps: software based ones and hardware based ones. The
> hardware based ones are generated by the chipset itself and have microsecond
> precision.
>
> If you use WinPcap on a standard network adapter (doesn't matter if it's
> wireless or not), you just have software timestamps.
>
> Let me know if this makes any sense to you.
>
> Have a nice day
> GV
>
>
> Cheers
>
> John
>
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