48
MDS TransNET 900 I&O Guide
MDS 05-2708A01, Rev. B
Invisible
place
holder
Figure 19. Extended SAF Network
Networks: J, K, L
Retransmission and ARQ operation
Functionally, the sub-network side of an Extension behaves like a
corresponding connection between a master and a remote.
When an Extension is using its “master personality” it sends
acknowledgments and performs unconditional retransmissions based on its
REPEAT
count.
When an Extension is using its “Remote personality”, acknowledgments are
processed and retransmissions occur as needed, up to the number of times
specified by the
RETRY
count value.
If new data arrives—from a new source—prior to completion of
retransmissions, then this is considered a violation of the polling model
protocol. The new data takes precedence over the old data and the old data is
lost. In such a situation, new data is bound to be corrupt as it will have some
old data mixed in with it.
Synchronizing Network Units
The Master controls the synchronization for a given network for all modes.
Setting the Master to “
SAF ON
” broadcasts a command from the Master to all
radio units in the associated network either directly or through an Extension
radio. This command puts all radios in the entire system in a special
time-division duplexing mode that alternates between two timeslots. One
time slot for data communications upstream and the second for downstream
communications.
X
K,L
R
L
R
L
M
J
R
J
R
J
X
J,K
R
J
R
K
R
K
R
L
Sub-Network J
Sub-Network K
Sub-Network L
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