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BID : 2425_EI2GYB
Subj: INTRODUCTION TO PACKET RADIO - Part 13
Sent: 181203/0715Z 2425@EI2GYB.DGL.IRL.EURO BPQ6.0.16
INTRODUCTION TO PACKET RADIO - Part 13 - by Larry Kenney, WB9LOZ
In this part of the series and the next we'll take a look at some of the
TNC commands available to you that we haven't covered previously. You
might find that some of the commands are not available in your particular
TNC or that they're used in a slightly different manner than what is
presented here. Not all TNCs operate exactly the same. Please refer to
your owner's manual for specific details on how to use these commands if
they don't function as described here.
8BITCONV: This command enables the transmission of 8-bit data in converse
mode. Used with AWLEN - see below. For normal packet operation, such as
keyboard to keyboard transmissions, use of bulletin board systems, and the
transmission of ASCII files, 8BITCONV should be OFF. If you need to
transmit 8-bit data, set 8BITCONV ON and set AWLEN to 8. Make sure that
the TNC at the receiving end is also set up this way. This procedure is
normally used for transmission of executable files or a special non-ASCII
AWLEN: This parameter defines the word length used by the serial
input/output port of your TNC. For normal packet operation, as described
above, AWLEN should be set to 7. Set to 8 only if you're going to send
AX25L2V2: This command determines which level of AX.25 protocol you're
going to use. If OFF, the TNC will use AX.25 Level 2, Version 1.0. If ON,
the TNC will use AX.25 Level 2, Version 2.0. Note: Some early TNCs will
not digipeat Version 2.0 packets. With AX25L2V2 OFF, if your TNC sends a
packet and the packet doesn't get acknowledged the first time it was sent,
it will send it again and again, until an "ack" is received or the TNC
retries out. With AX25L2V2 ON, if your TNC sends a packet and doesn't
receive an "ack" the first time, it will send a poll frame to see if the
other TNC received the packet. If yes, then it would continue, if not
then it would send the last packet again. The advantage here is that
short poll frames are sent, rather than long packets containing data.
This can greatly reduce channel congestion. For VHF/UHF operation, it
is almost essential that every TNC have AX25L2V2 ON. Many operators
have suggested that Version 2.0 NOT be used on the HF bands as it tends
to clutter the frequency with poll frames. See the CHECK command below
for related information.
BEACON: Used with EVERY or AFTER to enable beacon transmissions.
BEACON EVERY n - send a beacon at regular intervals specified by n.
BEACON AFTER n - send a beacon once after a time interval specified
by n having no packet activity on the frequency.
n = 0 to 250 - specifies beacon timing in ten second intervals.
1 = 10 seconds, 2 = 20 seconds, 30 = 300 seconds or
5 minutes, 180 = 1800 seconds or 30 minutes, etc.
For example, if you set BEACON EVERY 180 (B E 180), the TNC will transmit
a beacon every 30 minutes. If you set BEACON AFTER 180 (B A 180), the TNC
will transmit a beacon after it hears no activity on the frequency for 30
minutes. B E 0 will turn the beacon off. The text of the beacon is
specified by BTEXT and can contain up to 120 characters. The path used for
the beacon transmission is specified by the UNPROTO command. YOU SHOULD
USE BEACONS INTELLIGENTLY! Beacons are often a point of controversy in
the packet community because they tend to clutter the frequency if used
too frequently. You should keep your beacons short and infrequent, and
they should only be used for meaningful data. Bulletin boards use the
beacon for advising the community of who has mail waiting for them, clubs
use beacons for meeting announcements, and beacons are used for severe
weather warnings. In areas with heavy packet activity, beacons should not
be used just to let everyone know that you're monitoring the frequency,
that your mailbox is ready, or that you'd like someone to connect to you.
You should monitor the frequency for activity and make some connections
CHECK n: Sets a timeout value for a packet connection. When a connection
between your station and another seems to "disappear" due to changing
propagation, channel congestion or loss of the path, your TNC could remain
in the connected state indefinitely. If the CHECK command is set to a value
other than 0, the TNC will attempt to recover the connection or disconnect.
The action taken depends on the setting of AX25L2V2. The value of CHECK (n)
may be set from 0 to 250 and the timing is based on the formula of n * 10
seconds. (n = 1 is 10 seconds, n = 5 is 50 seconds, n = 30 is 300 seconds
or 5 minutes, etc. A value of 30 is a recommended value to use.) If CHECK
is set to 0, it disables the command. If AX25L2V2 is ON, the TNC will send
a "check packet" to verify the presence of the other station if no packets
have been heard after (n * 10) seconds. If a response to the "check packet"
is received, the connection will remain. If no response is received, the
TNC will begin the disconnect sequence, just as if the DISCONNECT command
had been sent. If AX25L2V2 is OFF, after no packets are heard for n * 10
seconds, the TNC will not send a check packet, but will begin the disconnect
CMSG: Enables the automatic sending of a connect message whenever a
station connects to your TNC. If CMSG is ON, the TNC will send the message
contained in CTEXT as the first packet of the connection. CTEXT can
contain up to 120 characters. Of course, you must have a message in CTEXT
for CMSG to function. This feature is often used when the station is on
but the operator is not present. The connect message is used to advise the
other station of that fact, and often says to leave a message in the TNC
buffer or mailbox. If CMSG is OFF, the CTEXT message is not transmitted.
KISS: KISS enables the TNC to act as a modem for a host computer,
allowing programs such as TCP/IP, the G8BPQ Packet Switch, various BBS
programs, and other programs using the Serial Link Interface Protocol
(SLIP) to be run. Before turning KISS on, set the radio baud rate and
terminal baud rate to the desired values. Set KISS to ON and then issue a
(continued in part 14)
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