Digi XBee S2C 802.15.4 User Manual page 39

Operation
802.15.4 protocol specifies eight security modes, enumerated as shown in the following table.
Level Name
0 N/A
1 MIC-32
2 MIC-64
3 MIC-128
4 ENC
5 ENC-MIC-32
6 ENC-MIC-64
7 ENC-MIC-128 Yes
The XBee/XBee-PRO S2C 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.
Effect on
maximum
Factor payload
Compatibility Force to 95
mode
Packet Reduce by 5 This penalty for enabling encryption is unavoidable due to the 802.15.4
overhead
Source Reduce by 6 This penalty is unavoidable because the 802.15.4 requires encrypted
address
Destination Reduce by 6 This penalty only applies if sending to a long address rather than a
address
App header Reduce by 4 The app header for encryption is 4 bytes long. This penalty only applies
Because of the two mandatory reductions when using encryption, no packet can exceed 116 - (5+6)
=105 bytes. The other options may further reduce the maximum payload to 101 bytes, 99 bytes, or 95
bytes.
When operating in API mode and not using encryption, if the source address is long, the receiving
device outputs an RX Indicator (0x80) frame for received data. But, if the source address is short, the
XBee/XBee-PRO S2C 802.15.4 RF Module User Guide
Length of message integrity
Encrypted? check
No 0 (no check)
No 4
No 8
No 16
Yes 0 (no check)
Yes 4
Yes 8
16
Comment
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.
protocol.
packets to be sent with a long source address, even if a short address
would otherwise be used.
short address.
if MM = 0 or 3.
Encryption
Packet length
overhead
0
9
13
21
5
9
13
21
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