FreeWave Technologies Inc. 1521131FFF Manuale Utente
Spread Spectrum Wireless Data Transceiver User Manual
LUM0002AG Rev A
Version 7.0
8
Choosing Point-to-Point or Point-to-MultiPoint Operation
A Point-to-Point network is limited to one Master and one Slave transceiver. Up to 4 Repeaters may be
added to extend the reach of the network, but no other Master or Slave may be added.
added to extend the reach of the network, but no other Master or Slave may be added.
In a Point-to-MultiPoint network (also referred to as MultiPoint network) the transceiver, designated as a
Master, is able to simultaneously communicate with numerous Slaves. In its simplest form, a MultiPoint
network functions with the Master broadcasting its messages to all Slaves and the Slaves responding to
the Master when given data by the device connected to the data port.
Master, is able to simultaneously communicate with numerous Slaves. In its simplest form, a MultiPoint
network functions with the Master broadcasting its messages to all Slaves and the Slaves responding to
the Master when given data by the device connected to the data port.
It is important to note the differences between Point-to-Point and MultiPoint networks. In a Point-to-Point
network all packets are acknowledged, whether sent from the Master to the Slave or from the Slave to the
Master. In a MultiPoint network, outbound packets from the Master or Repeater to Slaves or other
Repeaters are sent a set number of times determined by the user. The receiving transceiver, Slave or
Repeater, will accept the first packet received that passes the 32 bit CRC. However, the packet is not
acknowledged. On the return trip to the Master, all packets sent are acknowledged or retransmitted until
they are acknowledged. Therefore, the return link in a MultiPoint network is generally very robust.
network all packets are acknowledged, whether sent from the Master to the Slave or from the Slave to the
Master. In a MultiPoint network, outbound packets from the Master or Repeater to Slaves or other
Repeaters are sent a set number of times determined by the user. The receiving transceiver, Slave or
Repeater, will accept the first packet received that passes the 32 bit CRC. However, the packet is not
acknowledged. On the return trip to the Master, all packets sent are acknowledged or retransmitted until
they are acknowledged. Therefore, the return link in a MultiPoint network is generally very robust.
Traditionally, a MultiPoint network is used in applications where data is collected from many instruments
and reported back to one central site. As such, the architecture of such a network is different from Point-
to-Point applications. The number of radios in a MultiPoint network is influenced by the following
parameters:
and reported back to one central site. As such, the architecture of such a network is different from Point-
to-Point applications. The number of radios in a MultiPoint network is influenced by the following
parameters:
1.
Size of the blocks of data. The longer the data blocks, the smaller the network capacity.
2.
Baud rate.
3.
The amount of contention between Slaves. Polled Slaves vs. timed Slaves.
4.
Use of Repeaters. Using the Repeater setting in a MultiPoint network will decrease overall
network capacity by 50%.
network capacity by 50%.
For example, if the network will be polling Slaves once a day to retrieve sparse data, several hundred
Slaves could be configured to a single Master. However, if each Slave will be transmitting data at greater
levels, then fewer Slaves should be linked to the Master. The overall network will be closer to capacity
with fewer Slaves.
Slaves could be configured to a single Master. However, if each Slave will be transmitting data at greater
levels, then fewer Slaves should be linked to the Master. The overall network will be closer to capacity
with fewer Slaves.
For examples and additional information on data communication links, see the section Examples
of Data Communication Links later in this document.
of Data Communication Links later in this document.