Timewave PK-900, Operating Manual

Page: 82 / 392

In this case, the non-Lite station notices the non-standard bytes
following the control byte and issues a FRMR (Frame Reject) to signify
that a protocol violation has taken place. The PK-900 receives the
FRMR and automatically reverts to standard AX.25, sending the connect
retries without the Lite PID and address bytes.
3. WA1ABC>WB2XYZ [C,P] 01 3E 38 58 32 {Packet Lite attempt}
... {No response}
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.
4.11.3 Packet Lite Protocol Enhancement Summary
The following describes the Packet Lite protocol extension in depth
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 WA1ABC calls WB2XYZ:
Connect:
W B 2 X Y Z -0 W A 1 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 WA1ABC 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 WA1ABC. However, any combination of 26 bits may be used
(see "Technical Details" below).
Connect acknowledgment:
W A 1 A B C -0 W B 2 X Y Z -0 UA 01 58 32 3E 38
destination | source | CTRL PID | short address
WB2XYZ replies to WA1ABC. 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 WA1ABC,
and has shown his acceptance by echoing the address back in reverse
order (5832 = WA1ABC 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
1/93 4-40