52
MDS TransNET I&O Guide
MDS 05-2708A01, Rev. D
9.0 OPERATING PRINCIPLES AND CONFIGURATION
9.1 SAF Operation with Extension Radios
The Store-and-Forward (SAF) capability operates by dividing a network into
a vertical hierarchy of two or more sub-networks. (See
Figure 5 on Page 4
.)
Adjacent sub-networks are connected via Extension radios operating in
“
MODE X
” which move data from one sub-network to the next one.
The Store-and-Forward implementation adheres to the general polling princi-
ples used in most multiple-address systems (MAS). Polls originate from the
Master station, broadcast to all radios within the network, and travel hierar-
chically downward. All Remotes will hear the same message, but only one
Remote will respond. Messages within a hierarchy only travel in one direc-
tion at a time.
Using SAF will cut the overall data throughput in half, however, multiple
networks can be inter-connected with no additional loss in network
throughput.
Simple Extended SAF Network
The following example depicts a two-level network utilizing a single Master
(M) and an Extension (X) radio. See
Figure 17
.
Invisible
place
holder
Figure 17. Simple Extended SAF Network
Networks: J and K
In this network, messages directed to Remotes in the “K” sub-network, will
be relayed through Extension radio X
j,k
to the K-Remotes. Any response
from a Remote in sub-network “K” will pass back through Extension radio
X
j,k
to the Master M
j
. Radios in sub-network “J” operate on the same set of
frequencies and sub-network “K” but with a different radio-frequency
hopping pattern.
In the SAF operation, the Extension radios are set to
MODE X
(
Details Page 36
) and operate with a “dual personality”—50% of the time it
serves as a Remote station and 50% of the time as a Master for sub-network
Remotes.
M
J
R
J
R
J
X
J,K
R
J
R
K
R
R
K
K
Sub-Network “J”
Sub-Network “K”
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