MFJ-1270C/1274C MANUAL PACKET PROTOCOL
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Code Abbrv Frame Type
x1 RR Receive Ready
x5 RNR Receive Not Ready
x9 REJ Reject
03 UI Unnumbered Information
0F DM Disconnected mode
2F SABM Connect request
43 DISC Disconnect request
63 UA Unnumbered Acknowledge
87 FRMR Frame reject
even I Any frame ending in an even number (including $A,
$C, and $E) is an information frame.
Table 10-1 AX.25 Control Codes
I This and UI frames are the only frame types containing user data.The
control byte contains this frame's number and the number of the next frame
expected to be received from the other end of the link.
RR Usually used to acknowledge receipt of an I frame. The RR function can
also be performed by sending an I frame with an updated "expected next frame
number" field.
RNR Used when the buffer space on the receiving side is full.
REJ Used to request retransmission of frames starting from "x". Missed frames
are detected by receiving a frame number different from that expected.
DM Sent in response to any frame received other than a connect request
(SABM) when the TNC is disconnected. Sent in response to an SABM
whenever the TNC is on the air but can't connect to the requesting user, e.g., if
the TNC is already connected to someone else or if CONOK is OFF.
SABM Set Asynchronous Balanced Mode initiates a connect.
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