[Paul Offord <Paul.Offord@xxxxxxxxxxxx>]

Thanks Guy.

-----Original Message-----
From: wireshark-dev-bounces@xxxxxxxxxxxxx [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Guy Harris
Sent: 17 June 2016 06:41
To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
Subject: Re: [Wireshark-dev] PCAP-NG Timestamp Units

On Jun 16, 2016, at 9:47 PM, Paul Offord <Paul.Offord@xxxxxxxxxxxx> wrote:
 
> 
> The document PCAP Next Generation (pcapng) Capture File Format describes the timestamp value like this:
>  
> The timestamp is a single 64-bit unsigned integer representing the number of units since 1/1/1970 00:00:00 UTC.
>  
> The document doesn’t define “units”.  Is a unit a microsecond?

What the document says in the "Interface Definition Block" section:

	http://xml2rfc.tools.ietf.org/cgi-bin/xml2rfc.cgi?url=https://raw.githubusercontent.com/pcapng/pcapng/master/draft-tuexen-opsawg-pcapng.xml&modeAsFormat=html/ascii&type=ascii#rfc.section.4.2

is

	if_tsresol:

	The if_tsresol option identifies the resolution of timestamps. If the Most Significant Bit is equal to zero, the remaining bits indicates the resolution of the timestamp as a negative power of 10 (e.g. 6 means microsecond resolution, timestamps are the number of microseconds since 1/1/1970). If the Most Significant Bit is equal to one, the remaining bits indicates the resolution as as negative power of 2 (e.g. 10 means 1/1024 of second). If this option is not present, a resolution of 10^-6 is assumed (i.e. timestamps have the same resolution of the standard 'libpcap' timestamps).

	Example: '6'.

and in the "Enhanced Packet Block" section:

	http://xml2rfc.tools.ietf.org/cgi-bin/xml2rfc.cgi?url=https://raw.githubusercontent.com/pcapng/pcapng/master/draft-tuexen-opsawg-pcapng.xml&modeAsFormat=html/ascii&type=ascii#rfc.section.4.3

is:

	The Enhanced Packet Block has the following fields: 

		...

	* Timestamp (High) and Timestamp (Low): high and low 32-bits of a 64-bit quantity representing the timestamp. The timestamp is a single 64-bit unsigned integer representing the number of units since 1/1/1970 00:00:00 UTC. The way to interpret this field is specified by the 'if_tsresol' option (see Figure 10) of the Interface Description block referenced by this packet. Please note that differently from the libpcap file format, timestamps are not saved as two 32-bit values accounting for the seconds and microseconds since 1/1/1970. They are saved as a single 64-bit quantity saved as two 32-bit words.

So a "unit", for a packet that arrived on a particular interface, is whatever the time stamp resolution is on that interface.  The *default* meaning of a "unit" is 1 microsecond, but it can be set to other powers of 10 or 2, e.g. 1 nanosecond.

It should probably make it clearer what a "unit" is in the EPB section.  I'll look at improving that.
___________________________________________________________________________
Sent via:    Wireshark-dev mailing list <wireshark-dev@xxxxxxxxxxxxx>
Archives:    https://www.wireshark.org/lists/wireshark-dev
Unsubscribe: https://wireshark.org/mailman/options/wireshark-dev
             mailto:wireshark-dev-request@xxxxxxxxxxxxx?subject=unsubscribe

______________________________________________________________________

This message contains confidential information and is intended only for the individual named. If you are not the named addressee you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately by e-mail if you have received this e-mail by mistake and delete this e-mail from your system.

Any views or opinions expressed are solely those of the author and do not necessarily represent those of Advance Seven Ltd. E-mail transmission cannot be guaranteed to be secure or error-free as information could be intercepted, corrupted, lost, destroyed, arrive late or incomplete, or contain viruses. The sender therefore does not accept liability for any errors or omissions in the contents of this message, which arise as a result of e-mail transmission.

Advance Seven Ltd. Registered in England & Wales numbered 2373877 at Endeavour House, Coopers End Lane, Stansted, Essex CM24 1SJ

______________________________________________________________________
This email has been scanned by the Symantec Email Security.cloud service.
For more information please visit http://www.symanteccloud.com
______________________________________________________________________