Transmission, addressing, and routing Maximum RF payload size
XBee/XBee-PRO® S2C ZigBee® RF Module
93
high, the message fragments into a maximum of five fragments. The firmware encrypts and transmits
each fragment separately. The destination radio reassembles the fragments into a full message.
For Smart Energy firmware revision 5x32 and earlier, NP==0x80. As of 5x56, NP==0xFF.
The maximum payload is complicated to estimate for aggregator source-routing. To reduce the
maximum payload, when an aggregator sends a source-routed message it embeds the route into the
message as overhead, or into each fragment of the message, if fragmentation is necessary. If you use
APS encryption (EE1, Tx Option 0x20), it reduces the number further.
The route overhead is 2 bytes plus 2 bytes per hop. The bytes are:
n one byte is the number of hops
n one byte is an index into the route list that increments in value at each hop
n other data is a list of the 16-bit network addresses of the routing radios
Firmware revisions before 4x58 support a maximum of 11 aggregator source-routed hops. Firmware
revisions 4x58 and following support a maximum of 25 aggregator source-routed hops.
Aggregator source-routed payload maximums do not apply to messages that are sourced by non-
aggregator nodes, which send route records ahead of their messages to aggregators. Aggregators
are either Coordinators or Routers which have the following:
n Source routing enabled or
n AR setting which is not 0xFF
The following table shows the aggregator source-routed payload maximums as a function of hops and
APS encryption:
Hops Maximum encrypted payload Maximum unencrypted payload
1 255 255
2 255 255
3 255 255
4 255 255
5 255 255
6 215 255
7 205 250
8 195 240
9 185 230
10 175 220
11 165 210
12 155 200
13 145 190
14 135 180
15 125 170
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