[Sois-tcoa] Time Distribution

[Keith Scott]

And on the subject of time distribution...

I've attached the last message exchange on the subject of time distribution.
Going back over Chris's message, I think we should be able to knock out the
abstract service interface for time distribution right quick.  To that end I
propose the following service specification.  What other perameters do we
need?  Are there other services?

Although I dearly love abstract service specifications, I sort of like to
know they're realistic, so maybe we could come up with a couple example use
cases to see if this thing fits the bill, and to think about how one MIGHT
implement it (sort of an existance proof).

I didn't ask for meeting space in Athens to talk about this, let's see how
much progress we can make over email?

		--keith

====  Draft TD service specification  ====

Definitions:

Request Token: A handle passed from users of the time distribution service
when requesting the current time.  The token is returned in the time
response.  By supplying different tokens with different requests, a user can
associate responses with corresponding requests.

Accuracy Specification: An indication of the accuracy of a particular time
value (need to specify semantics here (units, at least) -- I suspect the
right verbiage exists if I can just find it.)  Will need to be able to
specify "no answer" (infinite variability) in case things fail.

Time Source Identifier: An indication of which TD time service 'master' the
user would like to use.  (In practice, a default value should yield 'any').

Timeout: A value indicating the maximum amount of time before an answer must
be returned.

TIME.REQUEST

The Time.request primitive shall be used by a user of the time distribution
service to request the current time.

Semantics: Time.request shall provide parameters as follows:
	Time.request ( request token,
			   accuracy specification,
			   time source identifier,
			   timeout)

When Generated: GetTime.request is generated by users of the time
distribution service when they want to request the current time.

Effect on receipt: Receipt of a Time.request shall cause the TD service to
determine the current time, to the specified accuracy, using the specified
time source.  If an answer cannot be provided by the timeout, the TD service
may return an answer with lower accuracy.



TIME.INDICATION

The Time.indication primitive shall be used to deliver the current time,
with specified accuracy and precision, to a user of the TD service.

Semantics: Time.indication shall provide parameters as follows:
	Time.indication(	request token,
				accuracy specification,
				time)

When Generated: Time.indication shall be generated in response to a
Time.request request.

Effect on receipt: The effect on receipt of a Time.indication by a TD user
is undefined.

Additional comments: The accuracy specification provided with a
Time.indication gives the accuracy of the accompanying time value.  We need
to specify some semantics here (units, at least).

============================

> -----Original Message-----
> From: Abhijit Sengupta [mailto:Abhijit.Sengupta at jpl.nasa.gov] 
> Sent: Monday, February 28, 2005 2:33 PM
> To: Stuart.Fowell at scisys.co.uk
> Cc: c.plummer at skynet.be; Massimiliano.Ciccone at esa.int; 
> Patrick.Plancke at esa.int; kscott at mitre.org
> Subject: Re: Draft TCOAS Web Page
> 
> 
> Some more comments - I put them in brown font in comment box. 
> (Strangely enough my previous comments got their date and 
> time changed and accordingly my previous comments have later 
> time stamp than the later comments - I guess artifacts of 
> Microsoft brilliance).
> 
> I am sending copy to Keith also for his comments on TDS.
> 
> Abhijit
> 
> At 2/28/2005 03:58 AM, Stuart.Fowell at scisys.co.uk wrote:
> 
> 
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