MFJ MFJ-1270C, Системное руководство

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MFJ-1270C/1274C MANUAL PACKET PROTOCOL
Page 231
which would have caused the collision, thus avoiding a fairly frequent source of
delay in versions of AX.25 prior to 2.0.
Channel Flow Control
Flow control of data through the link is determined by the rate at which data is
being supplied to a sending TNC and accepted from a receiving TNC.
A TNC receiving data from the link will send an RNR when the next I frame
successfully received will not fit into the buffer for output to the serial port.
Whenever a TNC transmitting data received from the serial port over the link
runs out of temporary buffer space, the serial port will be halted by an XOFF
character or CTS signal. In the MFJ-TNC implementation this happens
whenever there are 7 packets built and less than 210 characters left in the buffer
for input from the serial port.
When the TNC receiving data from the link clears out its buffers, it sends an RR
to the transmitting TNC. In order to guard against the possibility of the RR
being lost and the link becoming permanently locked, the transmitting TNC will
periodically re-transmit the packet that provoked the RNR. The receiving TNC
will continue to respond with RNR until it can accept the packet.