Networking
Encryption
Digi XBee® 3 802.15.4 RF Module User Guide
115
you use indirect messaging in a P2P network,
DH
and
DL
have to be set manually on the end device to
point towards the indirect messaging coordinator.
It is more difficult to use indirect messaging with pin sleep than with cyclic sleep because the end
device must wake up periodically to poll for the data from the coordinator. Otherwise, the coordinator
discards the data after
SP
*2.5 time, or 65 seconds, whichever is smaller. It is also important to keep
the pin woke device awake for
ST
time after receiving indirect messages, otherwise the coordinator
could attempt to transmit directly while the end device is asleep, and the transmission will fail. For
this reason we recommend only using indirect messaging with cyclic sleep.
Encryption
The XBee 3 802.15.4 RF Module supports AES 128-bit encryption. 128-bit encryption refers to the
length of the encryption key entered with the
KY
command (128 bits = 16 bytes). The 802.15.4
protocol specifies eight security modes, enumerated as shown in the following table.
Level Name
Encrypted?
Length of message integrity
check
Packet length
overhead
0
N/A
No
0 (no check)
0
1
MIC-32
No
4
9
2
MIC-64
No
8
13
3
MIC-128
No
16
21
4
ENC
Yes
0 (no check)
5
5
ENC-MIC-32
Yes
4
9
6
ENC-MIC-64
Yes
8
13
7
ENC-MIC-128 Yes
16
21
The XBee 3 802.15.4 RF Module only supports security levels 0 and 4. It does not support message
integrity checks.
EE 0
selects security level 0 and
EE 1
selects security level 4. When using encryption,
all devices in the network must use the same 16-byte encryption key for valid data to get through.
Mismatched keys will corrupt the data output on the receiving device. Mismatched
EE
parameters will
prevent the receiving device from outputting received data.
Working from a maximum packet size of 116 bytes, encryption affects the maximum payload as shown
in the following table.
Factor
Effect on
maximum
payload
Comment
Compatibility
mode
Force to 95
If
C8
bit 0 is set, all packets are limited to 95 bytes, regardless of other
factors listed below. This is how the Legacy 802.15.4 module (S1
hardware) functions.
Packet
overhead
Reduce by 5 This penalty for enabling encryption is unavoidable due to the 802.15.4
protocol.
