-68-
v6.3
802.15.4/ZigBee
Figure: Frequency channels in the 2.4GHz band
Channel Number
Frequency
Supported by
0x0C – Channel 12
2,405 – 2,410 GHz
PRO
0x0D – Channel 13
2,410 – 2,415 GHz
PRO
0x0E – Channel 14
2,415 – 2,420 GHz
PRO
0x0F – Channel 15
2,420 – 2,425 GHz
PRO
0x10 – Channel 16
2,425 – 2,430 GHz
PRO
0x11 – Channel 17
2,430 – 2,435 GHz
PRO
0x12 – Channel 18
2,435 – 2,440 GHz
PRO
0x13 – Channel 19
2,440 – 2,445 GHz
PRO
0x14 – Channel 20
2,445 – 2,450 GHz
PRO
0x15 – Channel 21
2,450 – 2,455 GHz
PRO
0x16 – Channel 22
2,455 – 2,460 GHz
PRO
0x17 – Channel 23
2,460 – 2,465 GHz
PRO
Figure: Channels used by the XBee modules in 2.4GHz
The XBee 802.15.4 modules comply with the standard
IEEE 802.15.4
which defines the physical level and the link level (MAC
layer). The XBee modules add certain functionalities to those contributed by the standard, such as:
•
Node discovery:
certain information has been added to the packet headers so that they can discover other nodes on the
same network. It allows a node discovery message to be sent, so that the rest of the network nodes respond indicating
their data (Node Identifier, @MAC, @16 bits, RSSI).
•
Duplicated packet detection:
This functionality is not set out in the standard and is added by the XBee modules.
With a view to obtain frames totally compatible with the IEEE802.15.4 standard and enabling inter-operability with other
chipsets, the
XBee.setMacMode(m)
command has been created to select at any time if the modules are to use a totally
compatible heading format, or conversely enable the use of extra options for node discovery and duplicated packets detection.
Encryption is provided through the
AES 128b
algorithm. Specifically through the
AES-CTR type.
In this case the Frame Counter
field has a unique ID and encrypts all the information contained in the
Payload
field which is the place in the 802.15.4 frame
where data to be sent is stored.
The way in which the libraries have been developed for the module programming makes encryption activation as simple as
running the initialization function and giving it a key to use in the encryption process.
{
xbee802.setEncryptionMode(1);
xbee802.setLinkKey(key);
}
Extra information about the encryption systems in 802.15.4 and ZigBee sensor networks can be accessed in the
of the Libelium website, specifically in the document: “Security in 802.15.4 and ZigBee networks”
The classic topology of this type of network is a star topology, as the nodes establish point to point connections with brother
nodes through the use of parameters such as the MAC or network address.
