User's Guide

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first (acknowledged) payload data transmission from a source to a sink will fail due to
the wrong response included in the datagram. However, the protocol will automatically
retry the transmission with the correct challenge. This happens transparently from the
application layer. The only impact is that the first payload data exchange will take twice
as long time as normally due to the retransmission.
3.3.6 Reliability
The delivery of payload data to the destination is very reliable. There are a number of
features build into the core of the protocol, which will help to increase the likelihood of
payload data being successfully delivered to the destination:
3.3.6.1 Node-to-node Ack/Nack
When neighbouring nodes communicate, the receiver of payload data responds with an
Local Acknowledge message if the CRC calculation on the received data is successful.
The sending node will retry the packet until either an Local Acknowledge has been
received, or until the packet is too old according to the TTL (Time To Live) parameter.
The sending node will always retry the packet to the neighbour, which is currently the
one closest to the destination. Should the missing Local Acknowledgements be a result
of the given neighbour no longer being within radio range, the neighbour will
automatically be removed from the neighbour list after a configurable number of times,
say three times for this discussion (see Configuration Parameters), missing Scheduled
Data transmissions. Once this has happened, retries of the packet will be done with the
neighbour now closest to the destination.
Theoretically there can be a situation where the data was received correctly at the
neighbour, but the Local Acknowledge was not received by the sending node. In this
situation, the neighbour will route the received packet onwards to the next node on
route to the destination. At the same time, the sending node will retry the packet. This
retry is now a duplicate of the previous packet. The receiving node will also route this
duplicate onwards to the next node on route to the destination. For Acknowledged
Transmission Type, once the packet reach the destination, the first packet will be
acknowledged, and a Ack will be routed back to the Originator. The second packet will
be Nack’d due to the challenge-response authentication failing. The Nack will be routed
back to the Originator, however the Nack will be ignored, because an Ack for the same
packet was already received. For Non-Acknowledged Transmission types, the duplicate
payload messages will be delivered at the application layer, and the application layer
will have to filter them out based on the included serial number which is supposed to be
unique for each payload datagram. See the Integration manual for further details on
how to send payload data, and which parameters are required for each type.