Full-duplex data transfer over radio modems

Full-duplex refers to a system which transmits and receives data in two directions at the same time. The telephone system is full-duplex as one can talk and listen simultaneously. A walkie-talkie is half duplex because a user can either receive or press the "talk" button to transmit. Half-duplex means that data can be transmitted in both directions on a signal carrier, but not at the same time.

Digi radio modems use a half-duplex radio channel but have full-duplex serial data buffers which allow the radios to simulate a full-duplex radio channel. The radios transfer data one direction while buffering data going the other direction. The radio channel will then switch directions to transfer the data in the reverse direction. This mechanism works best when the data transfer requirements are much smaller than the throughput available on theDigi radio modems.

Use these parameters to simulate full-duplex communication between two Digi RF Modems. These settings are only needed if communication may be initiated by two RF Modems simultaneously.

RR = 20
RN = 3

When streaming data, these settings enable "Reliable Delivery" communication and will arbitrate collisions by inserting up to RN random back-off delays after a collision; this allows a second radio to transmit data the other direction and simulates full-duplex communication. If one radio is sending data continuously the TT parameter may be used to force a RN delay to allow for other radios to send data back the other direction. Flow control may be enabled using the RT=2 parameter.

Last updated: Jun 19, 2019

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