CHAPTER 7
REPEATING FEATURES
Revised: 9 Sep 11
7-4
EST P/N AA107A
The following sections describe the process of the STP in the ESTeem Model 195Ea as how it would happen in the above example.
Learning Phase - Once properly configured, each Model 195Ea will begin to search out the other Model 195Ea units in radio range
that are programmed in the AP Repeater Peer table. All Model 195Ea’s will calculate their routes to every Model 195Ea in the
network based upon the lowest “path length” to the Root Bridge. Path length is the total number of wireless links (repeater peer
links) to transmit a packet through the wireless network to the Root Bridge.
Note
: The Root Bridge in a network should be the
Model 195Ea where the majority of the data flow is processed.
In every wireless network of two or more radios, the Root Bridge
should be user defined. If not defined, the ESTeem 195Ea with the lowest MAC address will be designated as the Root Bridge.
In Figure 4, the Plant network (Example 1) is the most logical location for the Root Bridge based upon the amount of data flow.
Setting this site as the root bridge is discussed below in Root Bridge.
Blocking and Forwarding Phase – To ensure you do not have a network loop situation due to redundant paths in your wireless
network, the Model 195Ea will recognize and disable (block) one or more redundant links and provide back up links should the
primary link fail. This establishes a wireless mesh network with a series of forwarding links, based upon the shortest path length to
the Root Bridge.
For example, looking at Figure 4, the Remote Building has two routes to the Root Bridge (Plant Network – Example #1); directly to
the site and through the repeater. The direct link between the two sites is the shortest route (lowest Path Length) and will be
selected as the primary route unless overridden by manually changing the Path Length in the configuration.
Path Length
If more than one communication path to the Root Bridge is found, the 195Ea must determine which route to take based upon the
lowest Path Length. The default path length to all links in the 195Ea network is 1. If the Path Lengths are equal then the lowest
MAC address will determine the priority route. In the ESTeem Mesh Network we want to directly control all data flow so do
not
want the routes to be automatically determined.
Looking again at our Example in Figure 4, if we made no changes to the default path length of 1 (note values in Figure 3) the lowest
path cost would be direct from the Remote Building to the Root Bridge (Plant Network).
Link Description
Total Path Length
Direct from Remote Building
1
Remote Build to Root Bridge Through Repeater
2
(Length 1 to re Length 1 to Master = 2)
To configure the 195Ea to select the repeater as the primary radio path, set the path length value for the direct link greater than 2
(such as a value of 3) to make this the primary radio path. The lowest path length will identify the highest priority. The Model
195Ea will use this routing, but also switch to direct communication if the repeater were to disappear.
Root Bridge
In any Access Point Repeater network consisting of more than two sites, one Model 195Ea should be designated as the Root
Bridge. Only one Model 195Ea can be designated as the Root Bridge in a given network and should be located where the majority
of the Ethernet data flow is processed. This site may be the Master location in a SCADA network or could be configured at a
repeater site. Selection is important because all Model 195Ea’s NOT configured as the Root Bridge will choose routing based
upon the Path Length to the Root Bridge. If you have any question as to which site in your AP Repeater application should be the
Root Bridge, contact ESTeem Customer Support at 509-735-9092 or e-mail your application to
.
The Root Bridge will be selected in one of two ways: the Root Bridge can be manually set (recommended) during the configuration
of the Repeater Peer table (Figure 3)
or
the Root Bridge designation will default to the lowest MAC address of all the Model
195Ea’s in the network. The manual Root Bridge configuration is located in the “Advanced Settings” section.