Image Processing Reference
In-Depth Information
Router
DeviceNet to
EtherNet/IP
IEEE
802.11
Wireless
device
AP
Wired
device
Wired
device
DeviceNet
EtherNet/IP
Wireless
device
FIGURE .
Extension of DeviceNet via a CIP router and an AP.
Router
DeviceNet
to WLAN
IEEE
802.11
Wireless
device
Wired
device
Wired
device
DeviceNet
Wireless
device
FIGURE .
Extension of DeviceNet via a WLAN-enabled CIP router.
connected to a conventional AP (see Figure .). In this case, no custom hardware component has
to be developed. However, this solution causes each message to traverse (at least) two intermediate
devices before reaching its target node (e.g., the router and the AP), and this introduces additional
delays.
A second and more sophisticated solution requires the existing DeviceNet routers to be modified,
to include an IEEE . port too, as shown in Figure . (likely, this should not be a difficult task
for manufacturers of DeviceNet products). In this case, as the wireless-enabled router is completely
aware of the exact requirements of each CIP connection (including details about its transport class
and expected packet rate), it can select the most suitable QoS when forwarding messages over the
radio channel. If a QoS-enabled network is adopted on the wireless side, such as for example IEEE
.e, an improved real-time behavior could be achieved.
It is worth noting that, at present, a couple of devices are available off-the-shelf that can be used
to implement wireless extensions to DeviceNet networks. For instance, the solution described in
Ref. [] relies on message routing to accomplish information exchanges over explicit connections.
In this case, a “wireless master” (implemented as a DeviceNet slave) is connected to the primary
DeviceNet bus, whereas one or more “wireless slaves” are used to connect separate DeviceNet remote
buses (every wireless slave is seen as the virtual DeviceNet master of the relevant remote bus).
To improve communication efficiency, a mechanism is also foreseen that makes wireless slaves col-
lect process data from the attached remote buses and provide them to the master as a single process
image. Unfortunately, solutions like this one are mainly based on proprietary wireless communication
technologies, and hence they can hardly be viewed as universal proposals.
