GE MDS SD Series Technical Manual page 59

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
local coverage area, keeping efficiency high. The transceiver achieves
these steps automatically, and does not require user input. The following
is an explanation of how this routing scheme is achieved.
Initially, all Remote device routes are unknown. The Master/AP
assumes that all undiscovered Remotes can potentially be on the SAF
link. Once a Remote attempts to communicate upstream to the
Master/AP, the Master/AP is aware of the Remote's path based on the
exchange type, direct or SAF. The Master/AP stores this information in
a database linked to the Remote's address. Future exchanges with the
Remote initiated by the Master/AP will reference this database and the
Master/AP chooses the most recent exchange type.
Upstream, the Remote can freely choose the best exchange type based
on what is available at the time. The Master/AP continuously updates
the routing database on each exchange to a Remote. If a Remote has not
been heard from within a certain time frame, the route is reset to initial
conditions so that the route may be "relearned." This does not cause any
additional delay and is implemented only as a safeguard. This allows for
highly efficient and adaptable routing to each Remote device without
the overhead of a routing protocol, and saves critical bandwidth.
MDS 05-4846A01, Rev. H SD Series Technical Manual 51