User's Manual

FreeWave Technologies Spread Spectrum Transceiver User Manual
900 MHz and 2.4 GHz
V5.0S
12
Overlapping Multipoint Systems
Overlapping multipoint systems may be set up with FreeWave transceivers
effectively if a couple of key parameters are set correctly.
Overlapping multipoint systems are defined as systems using different masters
which share or overlap in a specific geographic area. It may include colocation of
units (generally repeaters) which are part of different systems.
When colocating multipoint systems it is critical that the following parameters are
unique for each system:
Ø Network ID (unless using Call Book)
Ø Frequency Key
Ø Max Packet Size
Ø Min Packet Size
Setting Multipoint Parameters
(0) Number Repeaters
In a Multipoint network it is critical for timing purposes to know whether or not there
are repeaters in the network. Any transceiver that is used as a repeater essentially
becomes a master to the slaves and other repeaters to which it is communicating.
Therefore, the user must identify whether or not the network contains repeaters.
This is done by assigning a value in parameter (0), Number Repeaters. The value
should be 0 if there are no repeaters in the network and 1 if repeaters are present.
This parameter must be set to the same value in all units in a Multipoint network
(master, slaves, and repeater(s)).
(1) Master Packet Repeat
In point-to-point operation the FreeWave transceivers acknowledge every data
packet transmitted. In a Multipoint network, transmissions from a master to the
slaves are not acknowledged by the slaves. This is to prevent system overload. If
the slaves acknowledged all data transmissions from the master in a large
Multipoint system, then all system capacity would be spent having the master
listen for acknowledgments from the slaves. Because the transmission is not
acknowledged by the slaves 100% confidence does not exist that every slave has
received every message from the master. To address this issue the user may
modify option (1) Master Packet Repeat, assigning a value between 0 (the packet
is transmitted once) to 9 (the packet is transmitted 10 times). For networks with
solid RF links, this parameter would be set at the lower end of the scale (0-1). If
the network has some weak or marginal links it would be set toward the higher
values. If a slave receives a good packet from a master more than once it will
discard the repeated packets received. In addition, once a multipoint repeater
receives a good packet from the master it will discard any of the repeated packets.
In turn, the repeater will send the packet out (to the next repeater or to the slaves)
the number of times corresponding to its Master Packet Repeat setting. For more
information on this, see the next section, Master Packet Repeat in Multipoint
Systems with Repeaters.