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

Jean-Luc.Gerner at esa.int Jean-Luc.Gerner at esa.int
Tue Jan 15 07:38:02 UTC 2008

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>                                                     To 
             Sent by:                   sls-slp at mailman.ccsds.org            
             sls-slp-bounces at ma                                           cc 
             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                                        Subject 
                                        [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 6-1)
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 changes.

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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