Campbell Scientific RF401-series and RF430-series Spread Spectrum Data Radios/Modems - Manual (Page 122)

Appendix M. PakBus Networking Details
For example, a 1000 byte PakBus packet that is normally sent in 16 (64 byte)
RF packets will be sent in four (256 byte) RF packets. Reducing the number of
RF packets sent to the receiving radio minimizes the interleaving of RF
packets, which is a common cause of framing errors in the PakBus packets.
M.4 Establishing an Ad Hoc Point-to-Point Link
A point-to-point link with the destination radio is set up using the unique
PakBus address in the packet header, along with the source-destination address
of the radio module. The packet acknowledgement and retry features of the
radio module can be enabled using this point-to-point link. These features
provide a high degree of recovery from the inevitable RF packet collisions.
Packets sent to the radio using the PakBus broadcast address are transmitted
over the RF broadcast address, received by all radios, and not acknowledged.
In networks containing more than two radios, RF401s with OS3
or lower should not use retries if their protocol is set to
Transparent. Otherwise RF acknowledgements will collide.
M.5 Net and Radio Address Settings
The RF PakBus Protocol changes the Radio Address and Radio Mask settings
on a packet by packet basis when an ad hoc point-to-point link is established.
Therefore, the PakBus Aware and PakBus Node protocols ignore the Radio
Address and Radio Mask settings, and limit the available Radio Net addresses
to 0, 1, 2, or 3.
M.6 Hop Metric, Signal Strength, and Standby Modes
All configurations of the RF PakBus protocol (PakBus Aware, PakBus Node,
RF router or leaf) modify the hop metric in the Hello and Hello Response
messages. The modifications are based upon the radio standby mode (length of
duty cycling) and an averaged value of the signal strength for each node.
Basing the hop metric on the length of the duty cycle automatically provides
enough time for the long headers to propagate and wake up the receiving radio.
Basing the hop metric on signal strength allows the PakBus routing algorithms
to automatically take the best route without entering a Hello list that will
constrain the network. This only affects the system when a node has two RF
routes—one route that has good signal strength on each of the hops and another
route that is direct but has poor signal strength. Typically, the route with the
strongest signal strength is used, but the other route should not be eliminated.
The RF401 or RF430 will not reduce the hop metric, only increase it. The
radio compares the hop metric of the Hello message received by the radio (both
RF sourced and wire sourced) to a calculated hop metric based on duty cycle
and signal strength. The largest hop metric is used. Below is a more detailed
explanation about the method used to modify the hop metric.
NOTE
M-2