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

Greg Kazz greg.j.kazz at jpl.nasa.gov
Tue Jan 15 00:13:25 UTC 2008


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,


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