Timewave PK-232 MBX, Руководство по эксплуатации, Страница: 72 / 266

PK-232 OPERATING MANUAL PACKET RADIO
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 compressed 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:
0 A B C D E F G 0 0 H I J K L M 0 N 0 P Q R S T 0 0 u v w x Y Z
If we label the 7 standard right-justified callsign bytes 1-6 and SSID,
here is how we derive the first group of address-bits A-M:
ABCDE = (byte 1 XOR byte 4) AND $1F
FGHI = (byte 2 XOR byte 5) AND $0F
JKLM = (byte 3 XOR byte 6 XOR SSID) AND $0F
Timewave firmware derives the second group of bits N-Z the same way.
Other implementations are free to select any combination of 26 bits when
setting up the short address in either the initial SABM frame or its UA
response.
4.11 Packet Meteor Scatter Extension
A new packet protocol extension has been added for meteor scatter work
that allows a Master/Slave packet connection to be established. This is
done to reduce the possibility of simultaneous transmissions by both sides
of a packet connection over a long meteor scatter path.
This experimental protocol is activated by turning User SIT 18 ON (UBIT 18
ON). When UBIT 18 is ON (default OFF) the packet station that initiates a
packet connect will become the Master station and the station that
acknowledges the connect becomes the Slave.
After a Meteor Scatter connection has been established, the Master station
will continually send either information frames (I-frames) or polling
frames and await an acknowledgment from the slave. The Master station
therefore sends packets constantly, even if all its I-frames have been
acknowledged. The slave station sends nothing, not even I-frames, until
it receives a polling frame from the master. The Slave station may only
send an I-frame to the Master after a poll frame has been received.
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