PacComm TINY-2 - Packet Formatting and Timing

OPERATING INSTRUCTIONS Packet Formatting
must contain an integral number of 8-bit bytes. The TRACe
command enables the display of the address and control fields
of packets, as well as the text. The trace function displays all
bytes in hex as well as ASCII equivalents.
Packet Transmit Timing
Radio equipment requires a time delay for switching between
transmit and receive modes. If the packet controller starts send-
ing data before the transmitter is operating or before the
receiver has had time to switch from transmitting and lock up
on the incoming signal, the packet will not be received properly.
The delay between transmitter keyup and the beginning of data
transmission is controlled by the command elay. During
the time the packet controller is keying the transmitter but not
sending data, it will transmit a synchronizing signal (flags).
If you are transmitting packets through a voice repeater, you
may require a considerably greater keyup delay than is required
for direct communications. Furthermore, the extra keyup delay
is not required if the repeater has not had time to “drop” since
the last transmission. The command AXDelay allows you to
specify an additional keyup delay to allow the repeater receiver
and transmitter to lock up. The command AXHang sets the time
the packet controller will assume is required for the repeater to
drop. If the packet controller has detected channel activity
recently enough that the repeater transmitter should still be on,
it will wait only the TXDelay time before sending data, rather
than adding an AXDelay time as well. The commands TXDelay,
AXDelay, and AXHang ail set times in units of 10 ms.
Packet Timing
The AX.25 protocol provides for retransmitting packets if no
acknowledgment
is
heard
from
the
intended
destination
station
within
a
certain
period
of
time.
A
packet
might
not
be
acknow-
ledged
due
to
channel
noise
or
“collision”
with
another
packet
transmission,
and
since
there
may
be
other
stations
on
the
channel,
the
receiving
station
may
not
be
able
to
acknowledge
the
received
packet
immediately.
The
time
lapse
before
the
originating
station
retransmits
the
packet
is
set
by
the
command
FRack (frame acknowledge time). Do not set ck to a small
value
as
this
will
cause
unnecessary
retries,
especially
on
HF.
The
maximum
number
of
retransmissions
before
the
originat-
ing
station
terminates
the
connection
is
set
by
the
command
try.
The
maximum
number
of
transmissions
of
a
packet
is
REtry
+1,
since
the
initial
transmission
does
not
count
as
a
retransmission.
Setting
REtry
to
0
specifies
an
infinite
number
of retries.
Operating
Manual,
4th
Ed.
©
PacComm,
1990
25