PK-232 MBX – OPERATING MANUAL PACKET-RADIO
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WA1ABC sends data to WB2XYZ in Packet Lite format. The address field consists of the
short address from WB2XYZ's UA frame, reversed and left-shifted. The added bits come
from AX.25 version 2.0's command and response bits, and the end-of-address bit.
Acknowledgment of data:
BO 64 7C Fl 31
5832 shifted 3E38 shifted (RR,F;l)
short dest. short source CTRL
WB2XYZ acknowledges the data from WALABC. The address field is reversed. This is the
shortest length frame possible in Packet Lite. 4 address bytes + 1 CTRL byte + 2 flags +
2 CRC bytes = 9 bytes.
Every 10 minutes the stations must identify using both long and short addresses:
W B 2 X Y Z -0 W A 1 A B C -0 [RR,P;0] 0l 3E 38 58 32
destination | source | CTRL PID | short address
W A 1 A B C -0 W B 2 X Y Z –0 (RR,F;1) 01 58 32 3E 38
destination | source | CTRL PID | short address
Either station may initiate the ID exchange.
Disconnect:
W B 2 X Y Z -0 W A 1 A B C -0 DISC 01 3E 38 58 32
destination | source | CTRL PID | short address
Disconnect 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
At the end of the connection, the two stations must once again identify using both long
and short addresses.
Timewave firmware supporting Packet Lite also contains code that permits monitoring of
Packet Lite and extended AX.25 frames.
Packet Lite Shortened Address Technical Details
The Packet Lite address field consists of 26 bits distributed over 4 bytes (or 'octets', as the
AX.25 Spec calls them). These bits are considered to be two groups of 13 bits each,
roughly equivalent to a destination and a source ID. If we label the bits A-Z and show
their use in the address field of a Lite frame, the bits are distributed as follows:
A B C D E F G 0 x H I J K L M 0 N O P Q R S T 0 y U V W X Y Z 1
The least significant bit of each byte is used to show whether or not the byte is the final
byte in the address field, as in standard AX.25. The bits "x" and "y" (lower case) have the
function of command and response, similar to the function of the standard AX.25 version
2.0 SSID byte C bits (see AX.25 Protocol version 2.0, section 2.4.1.2).
In the Timewave implementation of Lite addressing, the standard callsigne are com-
pressed to yield short addresses. The destination callsign is compressed into bit:a A-M,
and the source into N-Z. These bits are used as the address field suggestion following the
control byte in the Connect (SARH) frame. When the bits are used following the control
byte as an ID suggestion or a real extended ID, the format is:
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