Wi-Fi Interface

There are two Wi-Fi interfaces available for use with ZentriOS, a wlan client (802.11 STA) interface and a softAP (802.11 AP) interface. Both interfaces share the same physical Wi-Fi radio and antennas. To set the Wi-Fi transmit power for both interfaces, use the common wlan.tx_power variable.

Likewise, to set the antenna used by both interfaces, use the common wlan.antenna.select variable.

WLAN Client Interface

The wlan client interface enables ZentriOS to join with a Wi-Fi access point at home, work or in-between. It is possible to use the wlan and softap interfaces concurrently, however these interfaces share the Wi-Fi radio and hence must operate on the same Wi-Fi radio channel in concurrent mode. The wlan interface has priority, and if the wlan interface starts on a different channel to the softap interface, the softap channel switches to the wlan channel.

ZentriOS provides various commands and variables to configure the wlan interface. See the documentation for wlan commands and wlan variables. An overview of WLAN functionality is provided in the following sections.

Scanning for Networks

There are two methods to scan for networks in range, active scanning and passive scanning. Active scanning involves the Wi-Fi module actively transmitting 802.11 probe request packets. When a Wi-Fi Access Point receives a probe, it replies with an 802.11 probe response. Passive scanning on the other hand avoids actively transmitting, and the Wi-Fi module simply listens for Wi-Fi Access Point beacons for a period of time on each channel scanned.

Each of the parameters discussed in the preceding paragraph (plus more) are configurable with ZentriOS. To specify the channels to scan, use the wlan.scan.channel_mask variable. The scan type (active or passive) can be set using the wlan.scan.type variable. The time spent listening on each channel, in active and passive scan mode respectively, is configurable using the wlan.scan.active_dwell and wlan.scan.passive_dwell variables. In active mode, the number of 802.11 probe requests is configurable using wlan.scan.num_probes.

To initiate a scan for Wi-Fi networks in range, use the wlan_scan command.

WLAN Security Type

ZentriOS supports all SOHO security types including Open, WEP, WPA & WPA2, and WPA2 mixed mode.

The wlan.security variable sets security type. The default value is Auto: ZentriOS determines security type automatically, from the network you are attempting to join. If you are planning to use WEP (and we sincerely hope you are not since WEP IS NOT SECURE), please read the instructions in wlan.security.

Joining a Network

To join a network manually, set the wlan.ssid and wlan.passkey variables to match the network name and network password the module is attempting to join. You can do this by setting the values of the variables directly. See Configuration and Setup for other provisioning methods.

See Procedure for Joining a WLAN Network

If your application is sensitive to latency or power, you should also consider customizing the number of join retry attempts with the wlan.join.retries.

To hide the passkey after it has been set, simply set the wlan.hide_passkey variable. After the passkey is hidden, it is no longer possible to read the passkey until a factory reset is performed. This stops an attacker learning the network password by physically acquiring a product with a ZentriOS device.

If the application requires the module to auto-join a network after boot up, set the wlan.auto_join.enabled variable. The number of automatic retry attempts and the delay between automatic retries is configurable with the variables wlan.auto_join.retries and wlan.auto_join.retry_delay.

Once the module is joined to a Wi-Fi network, the received signal strength (signal level) of the Wi-Fi Access Point is available with the wlan_get_rssi command.

Wi-Fi Roaming

If the signal strength of the Wi-Fi Access Point the module is joined with drops too low, the module attempts to scan for (and roam to) another known network in range. The received signal level at which roaming is initiated is configured using the wlan.roam.threshold variable. While the module is roaming on other radio channels, it may miss packets on the home channel. Depending on your application, it may be necessary to modify one or more of the wlan scan variables discussed in the Scanning for Networks section to minimize packet loss during roaming.

Access Point (SoftAP) Interface

The softAP interface enables a Wi-Fi client such as a notebook, smartphone or tablet to join with ZentriOS. The softap interface is primarily controlled with the softap variables:

SoftAP features:

Note: The SoftAP is limited to a maximum of 4 WLAN clients for ZentriOS on the AMW004 (Wallaby) and AMWx06 (Numbat) modules.