GDI SS900FH series, User Manual, Page: 19 / 40

GDI Communications Inc. LLC
9
APPLICATIONS
The following configurations are adjusted for optimum performance in a traffic communications network where
there is one Master/Local controller that initiates communications with Slave/Remote controllers. The SS900FH
provides the means for these controllers to communicate with each other over wireless networks.
GDI recommends that a site survey be performed before any installation of wireless modems. The survey
includes but is not limited to, Line-Of-Sight determination, Fresnel Zone calculations, and a spectrum analysis of
the area.
The Line-Of-Sight will determine the best placement of the antennas.
The fresnel zone calculations will determine antenna height .
The spectrum analysis will determine if there are any interfering signals in the area.
The SS900FH uses data Packetization for transmitting and receiving data. The SS900FH collects serial data from
the source controller until either the
Packetization Threshold (RB) is reached or one byte followed by
Packetization Timeout s (RO) of silence is detected. After which the SS900FH transmits the packet.
The transmitted data packet contains not only the data collected from the controller but also ID and addressing
information which insulates the SS900FH network from other devices operating in the same area.
Each receiver performs the following process when a
packet is received.
Packet recognition is the process by which the
SS900FH either accepts or rejects a data packet.
ID – All modems in a network must have the same ID
because SS900FH rejects any packet if it does not
have the same ID. On the other hand the ID
parameter can be used to isolate different
networks.
Figure 5 Packet Recognition