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PakBus Networking Guide

7.4.8 Broadcast Packets

The most common use of broadcast packets by a PakBus device is to send

beacons for link discovery and verification. The interval at which these

messages are sent is controlled by a beacon interval setting that is port specific

(the server has a similar setting for its PakBusPort device type). When beacons

are sent they are generally sent as an empty message with a high protocol code

of type PakCtrl.

There are other messages that can be sent to the broadcast address:

• When the server is going to hang up the link used by a PakBus port device,

it will send a "Goodbye" message with the destination set to the broadcast

address. This should have the effect of removing the server from any

neighbor's neighbor list. This will prevent the datalogger from attempting

to verify the neighbor on a link that is no longer functioning. Dataloggers

will also use the goodbye message when their tables are reset for various

reasons (such as changing the PakBus address).

• Under client control, the server will send a "Hello" command to the

broadcast address. For instance, this is done when the user selects the

"Search for Neighbors" option in the right click menu for the server in

PakBusGraph. There is a similar function in the setup screen. This is

actually an alternative form of beaconing but is one that will more reliably

give us a response (if a datalogger thinks it knows us as a neighbor, it won't

respond to a conventional beacon message).

• Dataloggers can be set up to send time update messages to a broadcast

message. This provides a means of keeping clocks of various devices in

close synchronization across a network.

In Log View (with PakBus Filter added) a broadcast packet might look like

this:

There are some characteristics that all broadcast messages share:

• Broadcast messages should not expect an immediate response.

• The transaction number either is ignored or is not present in the message.

• A broadcast message will never be forwarded. They will always be

exchanged between neighbors.

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Campbell RF410 Manual de Instruções Página 65