Encrypted Transmissions; Maximum Rf Payload Size - Digi XBee-PRO S2C Zigbee User Manual

Transmission, addressing, and routing
1. Set Bit 6 of DO to Enable High RAM Concentrator mode. High RAM mode means the aggregator
has sufficient memory to hold route records for its potential destinations.
2. Set AR to 0x00 for a one-time broadcast (which some nodes might miss), or a value in the
range of 0x01 to 0xFE (in units of 10 seconds) to periodically send a broadcast to inform the
network that the aggregator is operating in High RAM Concentrator mode and no longer needs
to receive route records.
3. Use Create Source Route - 0x21
device's source route table.
4. Send a unicast to the destination. The route record embeds in the payload and determines the
sequence of routers to use in transmitting the unicast to the destination. After receiving the
unicast, the destination no longer sends route records to the aggregator, now that it has
confirmed the High RAM Concentrator aggregator 'knows' its route record.
Clear the source route table
To clear the source route table, change the AR setting from a non-0xFF setting to 0xFF and complete
an AC command. To re-establish periodic aggregator broadcasts, change the AR setting to a non-0xFF
setting and complete an AC command.

Encrypted transmissions

Encrypted transmissions are routed similar to non-encrypted transmissions with one exception. As an
encrypted packet propagates from one device to another, each device decrypts the packet using the
network key and authenticates the packet by verifying packet integrity. It then re-encrypts the
packet with its own source address and frame counter values and sends the message to the next hop.
This process adds some overhead latency to unicast transmissions, but it helps prevent replay
attacks. For more information see

Maximum RF payload size

The NP command returns the maximum payload size in bytes. The actual maximum payload is a
function of the following:
message type (broadcast or unicast)
n
AP setting
n
APS encryption option
n
Source-routing
n
Broadcasts, which cannot be encrypted with APS or fragmented have a maximum payload of 0x54
bytes (84 bytes). Unicasts where AP is 0 also have a maximum payload of 0x54 bytes. A non-zero AP
means NP will be 0xFF or 255 bytes.
For broadcast messages and unicast messages when AP==0, the maximum payload is 0x54 bytes.
For unicast messages when AP is nonzero (API mode), the maximum payload is 0xFF (255 bytes)
bytes. If the combination of payload and optional APS encryption overhead (EE1, TxOption 0x20) is too
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.
XBee/XBee-PRO® S2C Zigbee® RF Module
to load the route record for a destination into the local
Zigbee security.
Encrypted transmissions
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