PK-232 MBX Operating Manual - N3UJJ

PK-232 OPERATING MANUAL
PACKET RADIO
3. WAlABC>WB2XYZ [C, P] 01 3E 38 58 32 {Packet Lite attempt}
…
In this case, the non-Lite station notices the non-standard bytes
following the control byte but sends no response at all. If this occurs,
you must turn the command LITE OFF and try to connect again to the distant
station. No adverse effects are caused by this, but transparency with
standard AX.25 is lost when the receiving station does not acknowledge a
Packet Lite connect request in some manner.
We know that TCP/IP, NET-ROM and DRSI stations ignore Packet Lite Connect
requests. These stations are normally found on VHF, but to be safe, the
LITE command should be turned OFF when not in use.
4.10.3 Packet Lite Protocol Enhancement Summary
The following describes the Packet Lite protocol extension in detail for
those interested in the technical details. It is not necessary to read or
understand the following section to use the protocol.
Here is a summary of a Packet Lite exchange, where WALABC calls WB2XYZ:
Connect:
W B 2 X Y Z -0 W A I A B C -0 SABM 01 3E 38 58 32
destination ⏐ source ⏐ CTRL PID ⏐ short address
The destination and the source are both 7 bytes long. Everything up to
the CTRL byte (SABM) is standard AX.25 version 2.0. The 'Protocol ID" of
01 hex is Packet Lite's reserved value, which provides a way of
interpreting the following bytes. This leaves room for other extensions
to AX.25 in the future. The short address bytes are the right-justified
bytes of the address field that WAIABC proposes to use in subsequent
Packet Lite frames with WB2XYZ. In this case, the AEA implementation of
the short address is illustrated. 3E38 is a compressed version of the
destination WB2XYZ and 5832 is a compression of WAIABC. However, any
combination of 26 bits may be used (see "Technical Details" below).
Connect acknowledgment:
W A I A B C -0 W B 2 X Y Z -0 UA 01 58 32 3E 36
destination ⏐ source ⏐ CTRL PID ⏐ short address
WB2XYZ replies to WALABC. Again, everything up to the CTRL byte (UA) is
standard AX.25. The 'PID' of 01 and the short address confirm that WB2XYZ
has accepted the Packet Lite connection. The short address is again the
right-justified representation of the address field that WB2XYZ will be
using in subsequent Packet Lite transmissions. In this case WB2XYZ has
accepted the short address field suggested by WALABC, and has shown his
acceptance by echoing the address back in reverse order (5832 = WALABC and
3E38 = WB2XYZ). AEA products always accept the short address from the
SABM frame; however, the Packet Lite protocol allows the sender of the UA
frame to propose a different combination of 26 bits, to avoid conflicting
with another Lite QSO. In either case, the sender of the original SABM
must accept the 26 bits in the UA frame, reversing the address order for
its own transmission
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