QKnxNetIpRoutingBusyProxy Class

Detailed Description

Depending on the configuration, a KNXnet/IP router or device can receive more datagrams than it can forward to the KNX subnetwork. This can lead to an overflow of the datagram queue and subsequent loss of one or more KNXnet/IP telegrams, because they could not be transferred from the network buffer to the queue to the underlying KNX subnetwork. Flow control is implemented by means of sending router busy messages to avoid the loss of datagrams due to overflowing queues in routers and devices.

A router busy message is sent by a KNXnet/IP router or device to notify all other devices that its incoming queue is filling up and it may loose datagrams if they do not stop sending. The message contains the state of the router or device (QKnx::NetIp::DeviceState), the timeout used to empty the incoming queue of the router or device, and the routing busy control field. The control field is set to 0000h, which requires all routers and devices to act upon receiving the router busy message.

The following code sample illustrates how to read the router busy message information sent by a KNXnet/IP router or device:

auto netIpFrame = QKnxNetIpFrame::fromBytes(...);

const QKnxNetIpRoutingBusyProxy proxy(netIpFrame);
if (!proxy.isValid())
    return;

auto busyTime = proxy.routingBusyWaitTime();

The sending device will wait for busyTime before sending the next frame.