Baseline Systems FreeWave Ethernet Radio User Manual
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User Manual and Reference Guide
LUM0024AB Rev A
Network Type:
MultiPoint
Default Setting:
3
Options:
Any number between 0 and 9.
Description:
In a MultiPoint network, Endpoints do not acknowledge transmissions from
the Gateway that are addressed for broadcast MAC addresses. If Endpoints
did acknowledge all broadcast MAC address transmissions, in a large network
the Gateway would soon become overwhelmed with acknowledgments from
the Endpoints.
Without acknowledgements, there is not 100% confidence that every Endpoint
has received every packet. To address this issue, you can modify the
Broadcast Repeat parameter, assigning a value between 0 (the packet is
transmitted once) to 9 (the packet is transmitted 10 times).
For networks with solid RF links, this parameter should be set to a low value such as 1 or 2. If a network has
some weak or marginal links, it should be set to higher values. If an Endpoint receives a good packet from a
Gateway more than once, it discards the repeated packets. Similarly, after a MultiPoint Repeater receives a
good packet from the Gateway more than once, it discards any further repeated packets. In turn, the Repeater
sends the packet out to the next Repeater or Endpoint(s) the number of times corresponding to its own
Broadcast Repeat setting. Increasing the Broadcast Repeat setting increases the probability of a packet
getting through.
In a network that contains transceivers set as a Repeater, all packets from the Gateway are considered
broadcast MAC address packets. Increasing the Broadcast Repeat setting in this type of network increases
the probability of a packet getting through, but it also increases latency and decreases Gateway-to-Repeater
and Gateway-to-Endpoint throughput in the network because each packet from the Gateway or Repeater is
being sent multiple times. Therefore, it is important to find the optimal mix between network robustness,
throughput, and latency. In general, a setting of 2 to 3 works well for most well designed networks.
In Endpoints, this setting determines how many times the Endpoint retries a packet of broadcast data before
taking the action set in the Slave Connect Odds parameter.
Note: The Broadcast Repeat may be set to 0 in the Gateway if the software is
capable of or requires acknowledgment. In this case, if the Gateway sends a
packet that the Endpoint does not receive, the software controls the retries, as
needed.
Broadcast Repeat in MultiPoint Networks with Repeaters
The Broadcast Repeat parameter must also be set in MultiPoint Repeaters because a Repeater appears as
a Gateway to an Endpoint. Therefore, the Repeater sends the packet out the number of times corresponding
to its own Broadcast Repeat parameter setting. If this parameter is set improperly, the reliability of the overall
network may be diminished.
For example, if a Gateway's Broadcast Repeat setting is 3, the link between the Gateway and Repeater
should be robust. If the Repeater's Broadcast Repeat is set to 0, this could cause marginal communications
between the Repeater and the Endpoints. The Endpoints communicating through this Repeater only receives
the initial packet from the Gateway with no repeats. Therefore, if the packet is not received on the first try, the
Endpoint does not respond as expected. This setting should never be set higher on a Repeater than on its
Gateway.
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