Unformatted text preview: multiple copies of the CLTU containing the “Frames”.
This systematic retransmission option is simpler to specify, compared to the ones discussed in sections
3.2.1 and 3.2.2. It probably needs less changes to the standards documents, which is an advantage
compared to those options. However, there are also some disadvantages to be considered, as
discussed in sections 3.3.1 to 3.3.5. Section 3.3.6 discusses the options for setting the Repetitions
parameter in the Transfer Sublayer. 3.3.1 Response to FOP-1 events
The option for systematic retransmission in the Synchronization and Channel Coding Sublayer would
be less responsive to FOP-1 events, such as the removal of frames from the Sent_Queue. So, when a
CLCW arrives which acknowledges a frame, the frame will still be retransmitted. This is inefficient, but
should not happen often if the option is correctly applied for a mission with a long light delay. 3.3.2 Physical Channel or Virtual Channel
If the option for systematic retransmission is in the Synchronization and Channel Coding Sublayer, then
the retransmission would be done at the level of the Physical Channel, after Virtual Channel
multiplexing. For missions with multiple Virtual Channels, it could cause unexpected disturbance to the
performance of the multiplexing algorithm, because all the systematic retransmissions of a frame must
be completed before another Virtual Channel can access the Physical Channel. So, for example, a
high-priority Virtual Channel could experience a longer delay than intended. Note that the delay would
affect all types of frames, including type-BD frames.
Systematic retransmission inside FOP-1 is done at the level of the Virtual Channel, so the Virtual
Channel multiplexing is unaffected. Another Virtual Channel can access the Physical Channel between
the individual retransmissions in a set of systematic retransmissions for a frame. TCretrans7 2008Sep09 I.B. + M.A. DE LANDE LONG
SOFTWARE + CONSULTANCY
Options for repeated retransmissions for telecommand Page 10 Of course, for missions which make no significant use of Virtu...
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This document was uploaded on 03/06/2014.
- Spring '14