[Sls-slp] Proposed Update to Proximity-1 Hailing Sequence

Jean-Luc.Gerner at esa.int Jean-Luc.Gerner at esa.int
Tue Jan 15 17:52:36 UTC 2008

You present this as individual entreprises separated by long 'idle' periods,
in what case it works. I am not sure this reflects the reality. Some
programmes may decide to reuse off-the-shelf equipment, compatible with the
current version of Prox-1.

So, I understand that the proposed change would not ensure backward
In order to go for a change of the standard after just 2 years of life, given
the risk that we cause non-compatibility between future missions, we need to
have a strong rationale showing:
- either that there is a well-identified risk of keeping the standard as is
- or the standard as is does not fullfil the system requirement of missions
in preparation

Your mail below is quite cryptic on this. It says that "In their testing,
members of the
>Electra team have identified the following modifications to the Space
>data link portion of the protocol". It does not say what the problem was.
Is there a non-conformance report available to substantiate the need for a

Sorry for appearing a bit nitty-gritty but I think that changing a standard
is a serious thing that needs to be carefully analysed before a decision is

Best regards
Jean-Luc Gerner
Tel: +31 71 565 4473

             Greg Kazz                                                       
             <greg.j.kazz at jpl.n                                              
             asa.gov>                                                     To 
             Sent by:                   Jean-Luc.Gerner at esa.int              
             sls-slp-bounces at ma                                           cc 
             ilman.ccsds.org            sls-slp at mailman.ccsds.org,           
                                        Gian.Paolo.Calzolari at esa.int, ed     
             15/01/2008 18:17           <Ed.Greenberg at jpl.nasa.gov>,         
                                        Peter.M.Shames at jpl.nasa.gov,         
                                        Charles.A.Edwards at jpl.nasa.gov,      
                                        sls-slp-bounces at mailman.ccsds.org,   
                                        tomg at aiaa.org                        
                                        Re: [Sls-slp] Proposed Update to     
                                        Proximity-1 Hailing Sequence         


I believe we ensure backward compatibility of Proximity-1 on an
enterprise  basis and for a specific time period. For example, for
the Mars enterprise for a given period of time (MER/MEX era) all
participating space agencies should agreed to operate the same
version of the protocol. The same principle should be extended to the
next generation of spacecraft at Mars (ExoMars, NASA Mars Scouts)
whenever these spacecraft need to interoperate with one another.


At 11:38 PM 1/14/2008, Jean-Luc.Gerner at esa.int wrote:
>Given that many developments have been made with the current version of
>Prox-1, one should make sure of full backward compatibility. How can we
>ensure it?
>Jean-Luc Gerner
>Tel: +31 71 565 4473
>              Greg Kazz
>              <greg.j.kazz at jpl.n
>              asa.gov>
>              Sent by:                   sls-slp at mailman.ccsds.org
>              sls-slp-bounces at ma
>              ilman.ccsds.org            Peter.M.Shames at jpl.nasa.gov,
>                                         tomg at aiaa.org,
>                                         Charles.A.Edwards at jpl.nasa.gov
>              15/01/2008 01:13
>                                         [Sls-slp] Proposed Update to
>                                         Proximity-1 Hailing Sequence
>Your comments on the following are welcome!
>Attached please find a word document containing a small enhancement
>to the current Proximity-1 Space Data Link Protocol Hailing Sequence
>in full and half-duplex. This modification was the result of the
>development of a reference implementation of the protocol at JPL by
>the Electra Transceiver Project. In their testing, members of the
>Electra team have identified the following modifications to the Space
>data link portion of the protocol. I believe these changes although
>slight, require a version change to that document, and cannot be
>considered Technical Corrigendum. Therefore, I propose a CCSDS BOF
>activity to be started now to solicit feedback on the proposed
>attached changes . My goal is to have sufficient time for all
>interested parties to review these proposed changes before the March
>meetings, so that we can move them out quickly for agency review thereafter.
>Summary of changes to Prox-1 hailing sequence:
> >1. Regarding the state transitions to S41 Radiate Carrier Only (Figure
>full duplex in E9. Also E37 in half-duplex as well.
> >In a space environment, we can see that it is reasonable to include
> >the E9 event (Valid Transfer Frame received) while in State S34
> >(Send Hail Tail) as a transition to S41. The tail idle sequence was
> >especially provided in the case that Convolutional Encoding was
> >provided in order to ensure that a sufficient number of bits went
> >through the convolutional decoder for the decoding process to
> >terminate. However in that process, we now see that it's possible
> >for the caller to receive a valid frame in state S34 before going to
> >S35. The same logic also applies to half-duplex. See attachment for
>2. Also, in the State Table for hailing, we are also recommending to
>CCSDS that the implementation note for transitioning from S35 to S41
>by achieving bit synchronization alone (i.e., valid frame not
>required) being an implementation specific transition be removed -
>since we cannot justify its existence anymore. The same
>implementation option will also be removed from the text for
>half-duplex as well. See attachment.
>Note that the Word revision feature does not allow for redlines of
>diagrams. Therefore in this text, I will note the changes to the two
>State Diagrams. All other changes are marked in RED and or strike out
>text where appropriate.
>Diagram changes:
>Figure 6 -1:  Full Duplex State Transition Diagram
>State S41 can now be reached in Event E9 from either S34 (new line
>from S34 to S41) or S35
>Figure 6-2: Half Duplex State Transition Diagram
>State S60 can now be reached in E14 (new line from S14 to S60) from
>either S14 or S36.
>best regards,
>[attachment "Prox1_Hailing_Sequence_Update.doc" deleted by Jean-Luc
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