Theory of Operation#

This section discusses the operation of the Wi-SUN Network Measurement application independently from the interface. You can execute these either through the CLI or the LCD screen interface. Specific interface information is shared in the following sections.

For the first step you need to start a Wi-SUN network using one of these solutions:

Follow the steps to get your border router up and running and move to the next chapter.

Flash the Application#

In the Simplicity Studio 5 Launcher perspective, select the EFR32 evaluation kit you want to use to run the Wi-SUN Network Measurement application. In the EXAMPLE PROJECTS & DEMOS panel, find the Wi-SUN - SoC Network Measurement project, and click CREATE to add it to your workspace.

Finally, build the wisun_soc_network_measurement project and flash it on the selected EFR32. Refer to the Quick Start Guide for the detailed steps.

Connect to a Wi-SUN Network#

By default, the Wi-SUN Network Measurement application tries to connect to the Wi-SUN Network. If a network with this name and a matching Wi-SUN PHY configuration is available nearby, the Performance Measurement node connects to it using the best parent node available (selected by the RPL routing protocol).

There are two solutions to change the default network name:

  • Using Simplicity Studio 5 prior to building the project: open the wisun_soc_network_measurement.slcp file and go to the SOFTWARE COMPONENTS panel. After you select the Wi-SUN/Application/Setting component, you can configure the default connection settings. Under Wi-SUN network configuration, modify the Network Name parameter to match the name of your Wi-SUN network.

  • Use the CLI available in the application. For more information, see Command Line Interface.

Each EFR32 radio board reference number defaults to a specific Wi-SUN PHY configuration matching its radio capabilities. To change the Wi-SUN PHY used by the project, refer to chapter 4 of UG495: Silicon Labs Wi-SUN Developer’s Guide.

Start a Ping Test#

You can trigger a ping test using either interface of the Wi-SUN Network Measurement application (LCD screen or CLI). The test consists of emitting ping packets on the Wi-SUN network to an IPv6 target (other Wi-SUN nodes or external IPv6 devices). This device replies with pong packets for each ping received. When the pong is received by the Performance Measurement node, the Wi-SUN Network Measurement application computes a round-trip latency on the communication link. During the test, the Wi-SUN Network Measurement application monitors several metrics to provide insights into the Wi-SUN stack behavior.

Retrieve Test Results#

After a ping test has ended, test results are available. They sum up the following information:

  • Ping packet loss percentage

  • Minimum ping latency in milliseconds

  • Maximum ping latency in milliseconds

  • Average ping latency in milliseconds

In addition to the ping test results, the Wi-SUN Network Measurement application also monitors metrics associated with the Wi-SUN stack.

Impact of Wi-SUN signaling on ping test results#

Due to the characteristics of a Wi-SUN network, where network management such as PAN advertising can take a certain time (it requires sending a PAN Advertisement on each channel, and there are often as much as 129 channels), using a ping to measure network latency needs to be taken cautiously.

Over several pings there will be mostly short ping durations, and some longer durations when network signaling takes precedence over data transmission. When network signaling occurs, the ping duration will be impacted.

The 'max' and 'average' ping results will be impacted by network management. To get a valid 'latency' value to compare between PHYs configurations, we'll only keep the 'min' ping duration of at least 100 pings in tables and graphs below. The ‘Wi-SUN SoC Network Measurement’ application is designed to allow this test.

Note: The network_size parameter will have a significant impact on these 'signaling perturbations'. The smaller network sizes use more frequent network signaling and therefore have the highest impact.

Wi-SUN Metrics#

To provide a better understanding on the Wi-SUN stack behavior the stack maintains internal statistics. The Wi-SUN Network Measurement application monitors several metrics during the tests:

  • Lifetime

  • MAC transmission count

  • MAC transmission failed

  • RPL rank

  • Expected Transmission Count (ETX)

  • Received Signal Level OUT (RSL out)

  • Received Signal Level IN (RSL in)

The metrics are maintained for each neighbor device in the routed network (that is, the parent and all of the children in the RPL mesh tree). Each metric is described in the following sections.

Lifetime#

The lifetime is a counter maintained with each neighbor to evaluate the state of the connection with this device. After each successful unicast communication with the neighbor, the counter is reset to 2200 seconds. When no unicast communication is exchanged with the neighbor, the counter is decreased each second.

MAC Transmission Count#

The MAC transmission count (or MAC TX count) represents the number of packets transmitted over the air. A single ping attempt can result in several MAC-level transmission if the first attempts have not been successful. The number also considers packets not related to the ping test itself. Packets routed by the device to its parent and network maintenance related communications also increase this number.

MAC Transmission Failed#

The MAC transmit failed (or MAC TX failed) represents the number of unsuccessful transmission attempts. In the Wi-SUN FAN specification, the peer must acknowledge every unicast packet. If a packet is not acknowledged within a given timeout, the transmission is considered failed. The packet is retransmitted by the Wi-SUN stack MAC layer until it reaches the maximum number of transmission attempts.

RPL Rank#

The RPL rank represents the rank or hop distance from the tree root (that is, the Wi-SUN border router). For more information, see section 3.5 of RFC 6550.

Expected Transmission Count#

The Expected Transmission Count (ETX) is an Exponentially Weighted Moving Average (EWMA) of the number of expected packet transmissions required for error-free reception at destination. The ETX is calculated as (frame transmission attempts)/(received frame acknowledgements) *128 with a maximum value of 1024, where 0 received frame acknowledgments sets ETX to the maximum value. This metric is maintained as part of the RPL protocol RFC 6550 and participates in the best parent selection.

Received Signal Level OUT#

The Received Signal Level out (RSL out) is an EWMA of the received signal level for the node-to-neighbor direction. The RSL is calculated as the received signal level relative to standard thermal noise (290°K) at 1 Hz bandwidth or -174 dBm. This provides a range of -174 (0) to +80 (254) dBm.

Received Signal Level IN#

The Received Signal Level in (RSL_in) is an EWMA of the received signal level for the neighbor-to-node direction. The RSL is calculated as the received signal level relative to standard thermal noise (290°K) at 1 Hz bandwidth (= -174 dBm). This provides a range of -174 (0) to +80 (254) dBm in 1 dBm steps. The RSL_in value is communicated through an information element in the Wi-SUN packet exchanges between the device and its neighbor.

Test Configuration#

The Wi-SUN Network Measurement application provides several settings to configure the ping test. The capabilities vary depending on the interface used but some of the configurations are shared:

  • Packet count: Defines the number of ping packets sent per target during the tests (default value 10). If the test targets the border router and the parent, 10 ping attempts would be sent to the border router followed by 10 attempts targeting the parent.

  • Packet length: Defines the payload size of the ping packet sent to the targets (default value 40). The size corresponds to the ICMPv6 payload including type field (1 byte), code (1 byte), checksum (2 bytes), identifier (2 bytes), sequence number (2 bytes), and finally data field (dependent on the packet length configuration).

  • Target devices: Defines which Wi-SUN devices are targeted by the ping test. There are three options:

    • Every known device, that is, the border router, the parent, and the device children

    • The border router

    • The parent

Note: If the device running the Wi-SUN Network Measurement application is connected directly to the border router, the parent device and the border router are equivalent.