For SCADA applications for process automation and monitoring, the flow of data is typically a command or polling request sent from the AP down to the EP followed by a much larger response containing the answer to the poll. So most data flows from the endpoints up to the access points or the UPLINK direction. By definition, TDD (Time-Division Duplex) radios spend part of the time transmitting (DOWNLINK) and part of the time receiving (UPLINK). Optimally, the radio air interface can and will be tuned to match the traffic patterns so that the use of the air interface is optimized.
cnReach supports the ability to tune how much time is allocated in each direction by adjusting the Tx and Rx Payload Bytes. For example, 256 Tx and 256 Rx will have 50/50 duty cycle and half the time is allocated in each direction. If you set it to 128 Tx and 512 Rx then the radios will have 20% downlink and 80% uplink which is perfect for SCADA.
BUT, what if there are times when you want to send more data to the End-Point? For example, configuration or firmware updates or remote management in general. A lesser known feature of cnReach is to enable 'Dynamic Payload'. With Dynamic Payload enabled, the AP simply gives any used downlink time to the EP's. So you can configure the Tx bytes to 512 and the Rx to 128 so the AP gets access to 80% of the bandwidth but when the AP has very little to send, like polls in normal operation, it gives the unused bandwidth to the EP's.
The net impact is that the spectrum usage is optimized for SCADA but still allows remote access and management. This feature is made possible by the software-defined air interface used by cnReach.
- Bruce