[Sis-dtn] Some thoughts on LTPv1's segmentation and length, etc

["구철회"]

All,


Let me share some thoughts on LTPv1's segmentation and length, etc with this WG.
Welcome to comments from you.


1. Segmentation aggregation
Segmentation aggregation could be useful in some specific circumstances from an operational perspective. However, implementing it can be quite challenging and daunting. It is closely related to the tolerance of design in LTP implementation, especially in buffering segmentation blocks. In a limited computing environment, there are limitations on considering wide-open design options. This would not be a favorable feature of LTP for interoperability.


2. Green-block
When using the Green-block and expecting similar actions as the Red-block simultaneously, certain limitations in the working environment should be expected to accommodate this scenario. In extremely low BER (Bit Error Rate), a long Green-block segment would make little difference from an application perspective. MTU is a useful practice on the ground test, but it may not work effectively in a space link. We are uncertain about how space link protocols will interact with laser communication technology.


3. Signal for link disruption
I agree that there is no need to include a signal for link disruption in the LTPv2 or not-LTP's specification book. However, I believe that having such a signal, which I would like to call a "cue," is a good practice for a spacecraft system in space. Although abrupt or unplanned link unavailability between space nodes is rare during operations, if it does occur, it creates a truly scary situation for ground operators, and no one would prioritize the DTN transaction until the spacecraft status returns to normal. Considering that link disruption can be mostly planned and expected in space in general, a "cue" signal would be beneficial for managing the outgoing buffer and related timers in LTP (or CLA). The "cue" would help mitigate the growth of retransmission buffer consumption and reduce the burden of handling timers.


Best,
Cheol





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Cheol Hea KOO
Principal Researcher, PhD
Mission Operation and Infrastructure Service Division
National Satellite Operation & Application Center
Korea Aerospace Research Institute
169-84, Gwahak-ro, Yuseong-gu, Daejeon, 34133, Korea
Phone : +82-(0)42-860-2145, 010-2044-7106
Fax : +82-(0)42-860-2605
Email : chkoo at kari.re.kr
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