Sierra Wireless EV-DO - Manual (Page 93)

Global Positioning System (GPS)
Rev 3.0B Feb.08 88
• Grouped ‐ Reports held until the total is equal or greater
than *PPSNFM which sets the packet size of grouped
reports.
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).
With Reliable Mode, *PPSNFR, enabled, 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 “window” 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.
Figure 9-11: AceManager : PinPoint - *PPSNFR, *PPMAXRETRIES
Simple Reliable Mode will ‘give up’ after a configured
number, *PPMAXRETRIES, of attempts and discard messages
that cannot be transmitted or received after that number of
tries.
Sending Reports Based on an Interval
You can configure the PinPoint‐E to send reports based on a
time interval and/or on the movement of a vehicle (based on
it’s position from one time to the next).