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Appendix M. PakBus Networking Details

M.3 Maximizing the RF Packet Size

The radio module’s RF packet size is changed from the default 64 bytes

to its maximum, 256 bytes, and the baud rate is increased to 38.4 kbps.

Changing the packet size and baud rate allows PakBus packets smaller

than 256 bytes to fit within one RF packet and larger PakBus packets to

use fewer RF packets. 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.

NOTE

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.

M-2

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