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PinPoint-E EDGE/GPRS - User Guide, version 2.32 47
Global Positioning System (GPS)
Store and Forward Reliable Mode
The Store and Forward Reliable Mode allows the PinPoint-E to ensure all messages are received
by the server even if the connection between them goes down for a period of time (such when a
vehicle passes through a location where the cellular signal is weak or non-existent).
FIGURE 19. Wireless Ace: Store and Forward Reliable Mode
With Reliable Mode enabled, *PPSNFR, the PinPoint-E will transmit a sequence number (1 to
127) as part of a packet of messages (may contain one or more reports). To reduce overhead, the
server only acknowledges receipt of every eighth packet. The PinPoint-E considers that 8 a “win
-
dow” of outstanding packets.
If the PinPoint-E doesn’t receive acknowledgement for a “window”, the modem will PING the
server with a message containing the sequence numbers of the first and last packets that haven’t
been acknowledged. The PinPoint-E will continue until the server acknowledges receipt. When
the PinPoint-E receives the acknowledgement, it will advance its “window” to the next group.
When the PinPoint-E is first powered on (or reset), it will send a Set Window message to sync up
with the server for the current “window”.
On the other side, if the server receives an out of sequence packet, it will send a message to the
modem noting the missing sequence and the PinPoint-E will retransmit.
GPS Time, Latitude, and Longitude can be added, *UDPRGPS, to the packet sequence data for
Reliable Mode.
FIGURE 20. Wireless Ace: Adding GPS Time, Latitude, and Longitude to Reliable UDP
data
Sending Reports
You can configure the PinPoint-E to send reports based on a time interval and on the movement of
a vehicle (based on it’s position from one time to the next).
Note: Using SnF Reliable Mode can cause excessive data traffic if the sequence
number is not returned.