PacComm TINY-2 - Channel Flow Control

PACKET
RADIO
PROTOCOL
Channel
Flow
Control
A
special
time
delay
(RESptime)
is
used
as
the
minimum
wait
time
prior
to
transmitting
acknowledgment
frames,
to
prevent
packet
controllers
accepting
data
at
high
speed
from
the
chronous
port
from
colliding
with
acknowledgment
frames
when
fewer
than
MAXframe
packets
are
outstanding.
The
receiving
packet
controller
will
wait
long
enough
before
sending
the
ACK
so
that
it
will
hear
the
data
packet
which
would
have
caused
the
collision,
thus
avoiding
a
fairly
frequent
source
of
delay
in
versions
of
AX.25
prior
to
2.0.
Channel
Flow
Comtrod
cence
Flow
control
of
data
through
the
link
is
determined
byt
at
which
data
is
being
supplied
to
a
sending
packet
controller
and
accepted
from
a
receiving
packet
controller.
A
packet
controller
receiving
data
from
the
link
will
send
an
when
the
next
I
frame
successfully
received
will
not
fit
into
the
buffer
for
output
to
the
serial
port.
Whenever
a
packet
controller
transmitting
data
received
from
the
serial
port
over
the
link
runs
out
of
temporary
buffer
space,
the
serial
port
will
be
halted
by
an
XOff
character
or
CTS
signal.
In
the
packet
controller
implementation
this
happens
whenever
there
are
7
packets
built
and
less
than
210
characters
left
in
the
buffer
for
input
from
the
serial
port.
When
the
packet
controller
receiving
data
from
the
link
clears
out
its
buffers,
it
sends
an
RR
to
the
transmitting
packet
con-
troller.
In
order
to
guard
against
the
possibility
of
the
RR
being
lost
and
the
link
becoming
permanently
locked,
the
transmitting
packet
controller
will
periodically
re-transmit
the
packet
that
provoked
the
RNR.
The
receiving
packet
controller
will
con-
tinue
to
respond
with
RNR
until
it
can
accept
the
packet.
_
Operating
Manual,
4th
Ed.
©
PacComm,
1990
45