The purpose of this guide is to help various engineers and decision makers understand limitations of the different protocols as well as guide deployment teams to design their networks around said limitations.
Large Networks do not behave in the same manner of small or medium-sized networks. While this statement is true, the definition of network size has changed somewhat during the last 10-15 years.
What was once considered a large network is now only of middling size as Digi’s XBee customers have begun deploying larger networks or many networks within a specific geographic region.
At this point in time, the following would be appropriate in terms of network size description.
2-20 nodes = Small Network
20-60 nodes = Medium Network
60 – 180 nodes = Large Network
180 + = While possible, it is not recommended / split up the network
It is true that there are networks that are functioning as desired that run larger than 180 nodes. However, these are hard to maintain and generally don’t allow for much data per node to traverse the network.
Let us look at a few scenarios and discuss what would be needed / appropriate for each in terms of protocol type and size of network.
Scenario 1: Remotely-Located Solar Farm with 10,000 radio nodes
In this scenario, which is actually more common than one would think, we have a solar farm in a remote location. This is relevant as outside RF interferers are less likely than in an urban environment.
This farm has 10,000 solar panel pylons that can track the sun on 3 axes. Each panel pylon requires an XBee radio to transmit or receive positional data as well as positional commands.
Each inverter platform handles up to ~400 of these panel pylons. To get a better idea of the scale of each section, along with distances involved, please refer to the image below:
On this particular solar farm, there are 50 inverter platforms. (They are seen above as little rectangles just off the roads going between sections)
Originally the customer wished to use as few networks as was possible. However, after trial and error, they found that too many nodes per network didn’t allow for timely or even reliable data transfer to occur. In the end, each platform hosted two gateways. Each gateway would handle up to 200 nodes as separate networks.
The main factors are as follows:
Scenario 2: Indoor Lighting on Single and Multiple Floors
Most of the same issues arise for this particular scenario with a few exceptions.
Scenario 3: Outdoor monitoring of various sensors in a highly dynamic environment
Dynamic environments, especially those that involve the nodes to be moving constantly, are not ideally addressed using the ZigBee protocol. The Digimesh protocol is much better suited to handle such environments. Nearly every other concern, previously discussed in the other applcations, is applicable. The biggest challenge is keeping network size and location manageable.
As node routes will constantly be changing, Directed Broadcasts are the suggested method that should be used to reach transmission destinations.
As with any new product or system, always deploy a test network that mimics as closely as possible the networks that will be deployed for use in real-world applications. This cannot be emphasized enough. A very large percentage of cost and headache comes when networks are deployed without proper testing. This stage will be money and resource well spent as it will help avoid costly updates, troubleshooting and replacement / repairs.