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SAC-PDG-SRFOM  July 2018

SAC-PDG-SRFOM July 2018

Subject:

Re: Need more information

From:

"Madden, Michael M. (LARC-D3)" <[log in to unmask]>

Reply-To:

SAC-PDG-SRFOM <[log in to unmask]>

Date:

Thu, 19 Jul 2018 15:25:49 +0000

Content-Type:

text/plain

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text/plain (1 lines)

Zack,

Question on rule 4-1. In your experience, if a distributed simulation had checkpoint-restart capability, would there be a need to permit HLA logical time to start at time other than zero? If so, then perhaps the general constraint is that HLA logical time must start at an integer multiple of the LCTS.

Michael Madden
Chief Engineer for Modeling and Simulation
Research Directorate
NASA Langley Research Center
Phone: 757-864-8399   Twitter: @Chief_Scientist

-----Original Message-----
From: SAC-PDG-SRFOM <[log in to unmask]> On Behalf Of Edwin Z. Crues
Sent: Tuesday, July 17, 2018 4:12 PM
To: [log in to unmask]
Subject: Re: Need more information

Hi Björn,

Okay, I think I’ve put together a solution. In all, I ended up adding 4 new rules. One of the rules was just an omission on our part (Rule 4-1). The other 3 are related, and along with existing time step rules should provide the specification you are looking for.

Here are the new rules:

Rule 4‑1: HLA Logical Time Starts at Zero (0)

Requirement: HLA Logical Time for a Space FOM compliant federation execution shall start at zero (0).

Rationale: Starting the HLA Logical Time for a federation execution at zero (0) makes the time computations easier and eliminates an additional configuration parameter.


Rule 4‑18: Federates Start On Common HLA Logical Time Boundaries (HLTBs)

Requirement: All Space FOM compliant federates shall start on common HLA Logical Time Boundaries (HLTBs).

Rationale: Time management and execution control requirements for Space FOM compliant federation executions and the associated Space FOM compliant federates require deterministically computable coordination points in the federation execution time line that can be achieved by all time constrained federates. Requiring Space FOM compliant federates to start time advancement on HLTBs along with associated time step rules provides this.

The basic equation for computing the next common is

HLTB = (floor(GALT/LCTS) + 1) * LCTS

where GALT is the Greatest Available Logical Time.


Rule 7‑23: Federation Execution Freezes On Common HLA Logical Time Boundaries.

Requirement: The freeze mode transition times computed by the Master Federate shall always be on a common HLA Logical Time Boundary (HLTB) in the future.

Rationale: Not all federates in a Space FOM compliant federation execution have the same time step. In order for all federates in the federation execution to freeze on a natural time step for any federate, the freeze time will have to be on a common HLA Logical Time Boundary (HLTB). This does not have to be the next available common HLTB but must be on a common HLTB in the future. Since the Master Federate sends out the ExCO with the Freeze mode transition, the Master Federate will determine the policy for computing the Freeze time at an HLTB in the future.


Rule 7‑24: Document Master Federate Freeze Policy in FESFA.

Requirement: The policy used by the Master Federate to compute common HLTB freeze transitions shall shall be documented in the FESFA.

Rationale: It is important that all federates in a Space FOM compliant federation execution understand the computational policy for computing freeze transition times (see Rule 7‑23). There may be some latency in the delivery of freeze mode transitions and some federates may require numerous time steps to prepare to go to freeze. Therefore, the policy used to compute freeze mode transition times must be documented in the FESFA, implemented in the Master Federate, and understood by all participating federates.


Note: Previous rule number have changed since some of these are inserted into existing series. Also, I believe that I’ve also adjusted the Rules vs. Roles matrix in Appendix G and the test matrix spreadsheet.

I’ll upload the updated documents to the Assembla site at the end of the day today.

Zack
*******************************************************************
* Edwin Z. Crues, PhD. | Phone: 281.483.2902 *
* Mail Code: ER7 | Mobile: 832.341.9023 *
* 2101 NASA Parkway | FAX: 281.244.6116 *
* NASA Johnson Space Center | Email: [log in to unmask] *
* Houston, Texas 77058, USA | *
*******************************************************************

> On Jul 17, 2018, at 6:25 AM, Björn Möller <[log in to unmask]> wrote:
>
> About the time steps:
>
> The question was:
> A federate has a time step (and thus Lookahead) of A. For example 100.
> If every federate starts at time zero, then the federate would request
> advancement to n*A (where n=1, 2, 3, 4, etc). Example 0, 100, 200, 300 When granted to n*A it would produce updates with time stamps (n+1)*A and finally request to be advanced to that time.
>
> But if a federate starts with some offset B, the time stamps would be n*A + B, for example 17, 117, 217, 317.
> In such case there would not necessary be any common boundaries for freeze, etc. So this should not be allowed.
>
> Do we have any rules that says this, directly or indirectly?
>
> Björn M
>
> From: SAC-PDG-SRFOM <[log in to unmask]> on behalf
> of Edwin Crues <[log in to unmask]>
> Reply-To: SAC-PDG-SRFOM <[log in to unmask]>
> Date: Monday, 16 July 2018 at 16:39
> To: "[log in to unmask]"
> <[log in to unmask]>
> Subject: Need more information
>
> Hi All,
>
> I am working through the Open Items in the SpaceFOMOpenItems.docx file. I have resolved many of them and only have a few left. However, there are a few items that I’m not really sure what they mean. I think that one item was from Björn and the other from Alfredo. I need a much better explanation of these items if I am going to be able to resolve them.
>
> Here they are:
>
> • Question: What are the requirements on a Time Stamp? Specifically, if a time step is 100, does the Time Stamp have to be 100 or can it be 101, 102, etc.?
> Answer: We need to make this a rule (see page 79). What??????
> Resolved:
>
> • Question: Do we need to indicate phase or role dependencies rules? Alternately, are there rules that can be violated during some execution phases?
> Answer: Does Appendix G - Rules Versus Roles Mappings address this question? Alfredo – can you give us an example?
> Resolved:
>
> Does anyone have a better statement/explanation of these questions? If not, I will have to leave them unresolved.
>
> Thanks.
>
> Zack
> *******************************************************************
> * Edwin Z. Crues, PhD. | Phone: 281.483.2902 *
> * Mail Code: ER7 | Mobile: 832.341.9023 *
> * 2101 NASA Parkway | FAX: 281.244.6116 *
> * NASA Johnson Space Center | Email: [log in to unmask] *
> * Houston, Texas 77058, USA | *
> *******************************************************************
>
>
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