Kantronics KPC-4 - KISS Mode

KISS Mode
The KISS Mode allows the TNC to act as a modem and packet assembler/disassembler
(PAD). The heart of the work to be done concerning what happens to data must reside
in your computer in order to use this mode of operation. The KISS code as designed by
Phil Karn is implemented to support higher level protocols for sharing computer
resources in a network fashion.
The most popular program using the KISS Mode of operation is TCP/IP or Transport
Control Protocol/Internet Protocol. This program will allow simultaneous file transfers
using FTP (File Transfer Protocol), user conversations using TELNET, and a Simple
Mail Transfer Protocol (SMTP). In addition, multi-connect capability is built into the
package, with the data being displayed only for the current "session". You can relate a
session to an I/O stream in the normal TNC operating mode.
In the KISS Mode, the TNC simply passes all received data to your computer, and the
computer program is responsible for all processing of that data, including decisions
concerning routing, digipeating, and other control decisions. The TNC converts the
synchronous data being received from the radio link into asynchronous data to be
passed to the computer over the serial port, and converts the asynchronous data from
your computer into the synchronous format suitable for radio transmission. The TNC
retains the responsibility for these functions, as well as determining proper timing for
channel access.
In the KISS Mode, channel access is determined by two settings in your TNC —
namely PERSIST and SLOTTIME. The algorithm used to determine whether or not
to transmit using this method has been shown to be considerably more sophisticated
than the DWAIT method used by most standard AX.25 packet stations. The result of
using the persistence algorithm is increased thruput under most channel conditions.
For our explanation of this algorithm, let's assume a PERSIST setting of 63 and a
SLOTTIME setting of 10. This slottime setting corresponds to 100 milliseconds.
When the TNC detects that the channel is clear and available (no carrier is detected),
it starts a timer (SLOTTIME). When the timer expires (100 ms in our case) the TNC
generates a random number between 0 and 255. If the generated number is equal to
or less than the PERSIST value, the TNC keys up the transmitter and sends the data
packet. With our setting of 63 the odds of this occurring after the first slottime are
about 1 in 4. (Actually the odds are PERSIST plus 1 divided by 256.) If the TNC
generated random number is greater than PERSIST, the TNC restarts the timer and
waits for the timer to expire again before generating a new random number. This is
repeated until the TNC gains channel access and sends its packet of information.
By carefully examining what happens, we can see that making SLOTTIME smaller
will cause the TNC to generate the random number more frequently, whereas raising
the
PERSIST
value
will
give
a
better
chance
(improve
the
odds)
of
transmitting
the
data.
Through
careful
choice
of
these
values,
it
is
possible
to
improve
data
thruput
while
at
the
same
time
permitting
shared
channel
usage
by
other
packet
users.
Data
received
from
the
radio
is
converted
into
asynchronous
format
by
the
TNC
and
sent
to
your
computer.
The
data
actually
sent
over
the
serial
port
is
formatted
with
special
control
information,
allowing
the TNC to determine
the
type
of
data
being
received
from
the
TNC.
KISS 35
© Copyright 1989, 1990, Kantronics, Inc. All Rights Reserved. A
Duplication of this manual or the firmware without Aug. 13, 1990 o Version 3.0
permission of Kantronics, Inc. is prohibited. Operations Manual