Re: fractional nanoseconds

[patrick diamond <pdseeker@xxxxxxx>]

Peter

I agree the extreme needs of some techniques are incomprehensible to others.

In the context of timestamp precision I wonder if a flag bit in the packet header to denote precision might work?

We could also simply use the extra bits when needed and exclude them when not?

Certainly the algorithms using the bits could be coded to tell the difference in timestamp field length.

Pat Diamond

On May 3, 2015, at 19:14, AshwoodsmithPeter <Peter.AshwoodSmith@xxxxxxxxxx> wrote:

LOL – yes I know ; )

 

My gut feeling is that as we get into 1/65535^th of a nanosecond we are well beyond the realm of the possible so that may be way too many bits.

 

One nanosecond is about 25cm in fiber. So we are talking .0004 of a cm!!!!

 

Seems like over kill to me but I’m not a clocking expert.

 

I can see doing this kind of overkill on periodic PTP packets where the bits don’t cost bandwidth, but here where every bit counts I think we need to be more frugal.

 

Cheers,

 

Peter

 

From: Jouni Korhonen [mailto:jouni.korhonen@xxxxxxxxxxxx]
Sent: Saturday, May 02, 2015 10:54 PM
To: AshwoodsmithPeter
Cc: marek.hajduczenia@xxxxxxxxx; STDS-1904-3-TF@xxxxxxxxxxxxxxxxx
Subject: Re: fractional nanoseconds

 

You would need to add 16 more bits to the timestamp. 

 

- Jouni

Sent from a smart phone.. Mind the typos..

"Peter.AshwoodSmith@xxxxxxxxxx" <Peter.AshwoodSmith@xxxxxxxxxx> kirjoitti 2.5.2015 kello 12.27:

where woukd the other 16 bits come from?


Sent from HUAWEI AnyOffice

From: jouni.korhonen

To: marek.hajduczenia;

Cc: STDS-1904-3-TF@xxxxxxxxxxxxxxxxx;

Subject: Re: fractional nanoseconds

time: 2015-05-02 15:14:23 Hi,

I was thinking the same as 1588 can do i.e. 1/65536 ns.

Jouni

Sent from a smart phone.. Mind the typos..

\> Marek Hajduczenia \ kirjoitti 2.5.2015 kello 9.32:
\>
\> Jouni,
\>
\> What would be the resolution of these fractional nanoseconds?
\>
\> Marek
\>
\> -----Original Message-----
\> From: stds-1904-3-tf@xxxxxxxx [mailto:stds-1904-3-tf@xxxxxxxx] On Behalf Of
\> Jouni Korhonen
\> Sent: Friday, May 01, 2015 6:30 PM
\> To: STDS-1904-3-TF@xxxxxxxxxxxxxxxxx
\> Subject: fractional nanoseconds
\>
\> Folks,
\>
\> We have already had some discussion on this topic earlier but.. what is your
\> opinion on having fractional nanosecond accuracy in the time stamping (e.g.
\> when sending a timestamp in the RoE header)? If we follow what 1588 did for
\> the correction field that would mean 16 additional bits, which may or may
\> not be significant overhead wise.
\>
\> Comments & opinions?
\>
\> - Jouni
\>
\> --
\> Jouni Korhonen, CTO Office, Networking, Broadcom Corporation
\> O: +1-408-922-8135, M: +1-408-391-7160
\>