airGATEWAY
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Application Note
15 LIMITATIONS IN THE NUMBER OF DEVICES
In its minimal extension, the “airLINK” network is composed of one Gateway and one Router or one End-
device.
To determine the maximum network extension, that is the maximum number of nodes that can be used in
the network, several factors must be taken into consideration:
1) Device addressing space: internal Gateway constraints limit the maximum number of devices internally
mapped to 112 (with addresses ranging from 16 to 127).
2) Maximum Number of End-Devices: The maximum number of end-devices that can, at any one time, be
'children' of a given Router (or Gateway) is 32. Practical questions of safety and redundancy recommend
having at least two possible parent routers for each End-Device installed, and this leads to use of at least
one router every 16 End-Devices.
3) Practical reasons recommend never exceeding the limit of 60 Routers.
16 NOTES ON THE RADIO COVERAGE OF THE DEVICES
The radio coverage of the devices is approximately one hundred meters in the open field, that is, without
the presence of any obstacles. In the closed field, the capacity is significantly reduced and highly variable,
depending on the individual case. Often dividing walls or reinforced floors can prove to be insurmountable
obstacles.
It is not always possible to determine the best position for the devices, particularly the routers, according
to theory; rather it must be determined empirically by trial during the actual installation.
17 NOTES ON BUILDING A NETWORK OF DEVICES
There are some practical rules for correct construction and installation of a network of “airLINK” devices.
1) When possible install the Gateway in a central position respect to the other nodes.
2) The Gateway must be able to communicate with at least two routers.
3) Each router must be able to communicate with at least two other routers.
4) Each router must not be able to communicate with more than sixteen other routers.
5) The number of routers must be calculated according to the number of End- Devices. Arrange at least
one router every 16 End-Devices.
6) Each End-Device must be able to communicate with at least two routers.
7) When possible install all devices in high positions and at a distance from metal masses.
8) When possible install the devices so that they fall within eyesight.
9) Limit the radio traffic as much as possible: experience has taught us that it is advisable to never
exceed an overall maximum number of messages every three seconds. This limit thus becomes the
minimum setting for the transmission frequency parameter for each node and this, in turn, depends on the
number of nodes in the network. If “n” indicates the number of nodes in the network, we recommend that,
for each node, the automatic transmission time must be set greater or equal than “3*n” seconds.