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The Radio System
The radio system used by the Sontay SonNet devices is divided into 3 sections or ‘layers’.
1.
The radio layer is where physical control of the radio signal is done. This conforms to international
standard 802.15.4, and determines the frequency of the radio signals, the number of ‘channels’
available for use, the bandwidth and power level of the signal etc. There are 16 channels available, and
the best one is automatically selected by the receiver. The frequencies used are in the ISM (Industrial,
Scientific and Medical) 2.4GHz band, with a maximum data rate of 250kb/s.
2.
The network management layer is where the self-‐healing tree functionality is run, which controls
network topology.
3.
The application layer determines what the device does – i.e. makes it a temperature sensing
device, a router or a receiver. SonNet devices use specific applications, and include features such as
configuration properties.
Security
All SonNet system devices have the same, unique network identifier. Only devices with the correct ID will be
allowed to join the network. The ID used by system devices is different from the ID used for site survey kit
(SSK) devices. Hence, SSK devices cannot join a system network and
vice versa
. When a SonNet system
network has been formed, it can be ‘locked’ to prevent any unauthorised devices joining, even if they are
SonNet devices. CMS can be used to subsequently authorise extra SonNet system devices if required.
All data transmitted by SonNet devices is encrypted using AES 128.
How the Wireless Network is Formed
The network is formed based on 3 rules, and in a specific order of priority.
1.
How many ‘hops’ a device is away from the receiver.
If a device can communicate directly with the receiver, it will, even if the link quality is poorer than if it
went through a router or RF-‐IOM. If a device has a choice of more than one router or RF-‐IOM, it will
choose the router or RF-‐IOM closest to the receiver (the least number of hops away),
even if the link
quality is poor
.
2.
The number of ‘child’ devices a router or RF-‐IOM already has.
A RF-‐IOM or router can have a maximum of 16 ‘children’. If a device has a choice of more than one RF-‐
IOM or router of the same ‘hop’ level, it will choose the router or RF-‐IOM with the least number of
children,
even if the link quality is poor
.
3.
Signal Strength (link quality).
Finally, if a device has a choice of more than one RF-‐IOM or router of the same tier level and the same
number of children, it will choose the router or RF-‐IOM with the best link quality.
If, for any reason, a device (ED, RF-‐IOM or router), loses its preferred path back to the receiver, it will
automatically search for an alternative – still obeying the 3 rules above in sequence. If, despite
employing Direct Sequence Spread Spectrum (DSSS) techniques, interference on the currently occupied
channel prevents communications, the receiver will automatically look for another channel which is
clear. All other devices, having lost their links to the receiver, will then also automatically scan the 16
channels until they find the receiver again, and the network will re-‐form without user intervention.
Summary of Contents for RF--RXS--B
Page 1: ...INNOVATION QUALITY COMMITMENT SUPPORT experts in field controls RF RXS B System USER MANUAL...
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Page 34: ...Page 32 of 87 Typical sensor properties Typical RF IOM properties...
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