Subject: [TICTOC] RE: TICTOC Digest, Vol 6, Issue 13

From: "Jeremy Bennington" <[email-masked]>
Date: Tue, 16 Jan 2007 05:42:43 -0800

Sasha & All,

Frequency is actually easier in a large scale packet network than time.
In today's implementations where high quality frequency is needed the
client can use a high quality oscillator and use that to average out the
jitter it sees in the packet flow.  With frequency it does not matter
what edge of the clock is lined up.  With time it does matter, every
edge of the frequency clock is named.  Timing over a packet network
cannot be solved by using a high quality oscillator at the client,
instead or in addition to that, your need to address the network
constraints and implement more complex server/client relationships.

Both syntonization and synchronization are impacted by hop count,
bandwidth utilization and manufacture/model differences (ie. No two
routers/switches are the same).   

Regards,

Jeremy B.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] 
Sent: Monday, January 15, 2007 10:59 PM
To: [email-masked]
Subject: TICTOC Digest, Vol 6, Issue 13

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Today's Topics:

   1. RE:  Draft BOF description (Sasha Vainshtein)

----------------------------------------------------------------------

Message: 1
Date: Tue, 16 Jan 2007 08:57:59 +0200
From: "Sasha Vainshtein" <[email-masked]>
Subject: RE: [TICTOC] Draft BOF description
To: "Marshall Eubanks" <[email-masked]>
Cc: Alon Shtern <[email-masked]>, [email-masked]
Message-ID: <[email-masked]>
Content-Type: text/plain;	charset="us-ascii"

Marshall and all,
A couple of questions stemming from you last message to the list:

1. Do I understand correctly that the relativistic effects you have
mentioned affect
   synchronization but not syntonization (at least if we restrict
ourselves to
   the objects that stay in the same place on the surface of Earth)?

2. Do I further understand correctly that verifiable quality of
synchronization
    depends on the distance between the server and the client while the
    verifiable quality of syntonization does not depend on that (at
least in theory)?

Regards,
                   Sasha

-----Original Message-----
From: Marshall Eubanks [mailto:[email-masked]]
Sent: Monday, January 15, 2007 7:24 PM
To: Stewart Bryant
Cc: [email-masked]
Subject: Re: [TICTOC] Draft BOF description

Dear Stewart;

On Jan 15, 2007, at 11:20 AM, Stewart Bryant wrote:

> Marshall Eubanks wrote:
>
>> Hello;
>> I will ask again the questions I asked in San Diego :
>> What are the accuracy goals of this work, for both synchronization 
>> and syntonization ?
>> What is the expected integration time ?
>> What is the expected geographical area over which these goals are   
>> likely to be met ?
>> Is this effort designed to replicate or instantiate ITU G.8261 ?  
>> To  support TDMoIP ? Some other standard ?
>> In my experience, timing does not lend itself to a "let's make it as

>> good as possible" mode of
>> development, as the most important question is generally, what   
>> complications can I leave out and still meet my goals ?
>
> Sure you have to know what you can acheive in a particular network 
> environment - i.e. is this network and this technique good enough and 
> reliable enough to serve this need ... but... there is a very large 
> range of applications that need time and the result is a range of 
> requirements that range from NTP style 10ms to rather better than we 
> can expect to do ns. From a rough survey of the applications it looks 
> like we need to get from 10ms class to 1us class to satisfy the 
> majority of the demand. However unlike the original assumptions make 
> in the NTP design, I think that we can make requirements on the 
> network to achieve high end performance.
>

Global relativistic synchronization effects start coming at 4 . 10^-7
sec, assuming that your network is restricted to be on the surface of
the Earth, so they shouldn't be ignored even at the microsecond level,
if you want the domain of your synchronization to be global.  
Things are worse if parts of your network are on an airplane, or in LEO;
note also that time dilation effects for LEO are order 6 * 10^-10 s/s,
and 10^-8 in deep space.

> (I derived the initial IERS standards for VLBI differential

>
> I am not familiar with either of those FLAs

Here is the paper referred to

http://www.iers.org/documents/publications/tn/tn32/tn32_109.pdf

Regards
Marshall

>
>> In order to be specific, I assume that one purpose here is meeting 
>> the TDMoIP accuracy discussed in the ITU SG15, which is roughly 10^-6

>> sec and 10^-8 s/s. Does that mesh with other people's expectations ?
>
> Support for Circuit Emulation and Mobile Phone base stations are the 
> two primary drivers for frequency. I think that PDV measurement is the

> poster child for time, but as I mentioned in my earlier message today 
> there are end user applications that also need time in the 1us class.
>
>> I would be willing to participate in but not take the lead on writing

>> the requirements document.
>
> Thanks
>
> Stewart

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