GE MDS SD Series Technical Manual page 56

Figure 31 below depicts a typical single unit SAF network. This network supports a single SAF
hop. Chained SAF hops are not allowed. However, multiple SAF radios are supported provided
their RF coverage areas do not overlap, as this would create radio interference and severely re-
duce throughput. SAF will work in conjunction with repeater assemblies to provide even more
extended range.
NOTE Remote radios being served by a Store-and-Forward unit must have their TX/RX fre-
quencies set to match those of the AP/Master station. This allows communication with
the SAF radio, which uses standard Remote TX/RX frequencies.
Store and Forward is available in Packet w/MAC mode and supports all MAC features including
collision avoidance, retries, and acknowledgements. Furthermore, all major radio features are
supported in SAF networks such as diagnostics, over the air programming, bridging, VRCs, etc.
Dual Duty of SAF Remotes: Since a SAF device doubles as a Remote radio it may participate
in direct exchanges with the Master/AP. By design, an SAF device is always within the primary
coverage area and has direct communication to the Master/AP. Therefore, all SAF devices act as
both a standard Remote for direct exchanges, as well as an SAF unit for Store and Forward ex-
changes. A SAF exchange is defined as any exchange between the Master/AP and a Remote
through an SAF device. In all cases, the Master/AP still controls the operation of the network.
After sending a SAF data frame, the Master/AP remains idle until the frame has been delivered
to the Remote, at which time it will return to direct or SAF operation, depending on the message
type (unicast or broadcast).
Direct vs. SAF Traffic: Depending on network topology, it is possible for some Remotes to
hear both direct polls from the Master/AP and SAF messages from an SAF-designated Remote.
It is more desirable to use the direct traffic to avoid the latency of going through the SAF link,
and the radio's firmware handles this situation automatically. SAF frames are ignored when the
direct path is available. The system is dynamic; if the direct path becomes unavailable for any
reason, it quickly switches to the SAF path to provide continued operation.
Traffic Routing: Typically, network radios are immobile, but fading may cause paths to come
and go. Because of this, the Master/AP device implements routing to each Remote device. This
ensures that only SAF traffic passes through SAF Remotes. Direct traffic is terminated at the lo-
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Figure 31. Store and Forward System Example
SD Series Technical Manual MDS 05-4846A01, Rev. I