Flaw in using the quietest channel for the network (Ember)

[triller-telekom]

The EmberNetworkInitialisation class creates the zigbee network via

public void formNetwork(EmberNetworkParameters networkParameters, ZigBeeKey linkKey, ZigBeeKey networkKey) {
.
...
.
    if (networkParameters.getRadioChannel() == 0) {
            networkParameters.setRadioChannel(quietestChannel);
    }
.
...
.
}

The problem is, that the ZigBeeDongleEzsp which calls this formNetwork method, initializes the networkParameters during its initialization as follows:

// Get the current network parameters so that any configuration updates start from here
networkParameters = ncp.getNetworkParameters().getParameters();

As far as I understand it, this means that networkParameters.getRadioChannel() will always contain the channel that is set on the chip and thus never 0.

UNLESS one calls ZigbeeNetworkManager#setZigBeeChannel(ZigBeeChannel channel) between the ZigbeeNetworkManager#initialize() and ZigbeeNetworkManager#startup().

This boils down to the problem of setting a channel that satisfies the check from above: networkParameters.getRadioChannel() == 0.

The naive approach with

networkManager.setZigBeeChannel(ZigBeeChannel.create(0));

results in

ZigBeeDongleEzsp] - Unable to set channel outside of 2.4GHz channels: CHANNEL_00

The error occurs due to this check in ZigBeeDongleEzsp:

public ZigBeeStatus setZigBeeChannel(ZigBeeChannel channel) {
        if ((ZigBeeChannelMask.CHANNEL_MASK_2GHZ & channel.getMask()) == 0) {
            logger.debug("Unable to set channel outside of 2.4GHz channels: {}", channel);
            return ZigBeeStatus.INVALID_ARGUMENTS;
        }
        networkParameters.setRadioChannel(channel.getChannel());
        return ZigBeeStatus.SUCCESS;
    }

---

As a solution to this problem I think the check in formNetwork should be changed to:

if (networkParameters.getRadioChannel() == ZigBeeChannel.UNKNOWN.getChannel()) {
            networkParameters.setRadioChannel(quietestChannel);
}

And the check for setting a zigbee channel in ZigbeeDongleEzsp should be extended to allow for setting the UNKNOWN channel, which then means "Use auto detection to find the quietest channel":

public ZigBeeStatus setZigBeeChannel(ZigBeeChannel channel) {
        if (channel != ZigBeeChannel.UNKNOWN && (ZigBeeChannelMask.CHANNEL_MASK_2GHZ & channel.getMask()) == 0) {
            logger.debug("Unable to set channel outside of 2.4GHz channels: {}", channel);
            return ZigBeeStatus.INVALID_ARGUMENTS;
        }
        networkParameters.setRadioChannel(channel.getChannel());
        return ZigBeeStatus.SUCCESS;
}

However, I am also wondering why there is a check for the 2GHz band in there. Is there any regulatory that Ember chips must only be used within this frequency band?

---

I also had a look at the telegesis implementation, but I think this feature is not implemented (yet), at least I didn't see it in the transport implementation.

[cdjackson]

Hi Stefan,
I think from a quick look at your proposal that it sounds ok.

However, I am also wondering why there is a check for the 2GHz band in there. Is there any regulatory that Ember chips must only be used within this frequency band?

ZigBee defines channels outside of 2GHz so we can't really do this - it is perfectly possible for the Ember chipset to use these frequencies. If the code that restrict this then we may need to remove that restriction at some point in future. Currently the 868MHz band is possible, and I understand that 915MHz will also be opened up in future (that said, these frequencies are currently only defined for use with Smart Energy but there are other users I know of looking at using ZigBee devices on these bands for added range).

Possibly also linked to #958.