The World of Computer Software/The World of Computer Software.iso/nosvw137.zip/AX25

Text File | 1991-09-18 | 14KB | 343 lines

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ax25
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ax25 bc <interface>
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The 'ax25 bc' command routes beacon broadcasts via <interface>.

>> Example:  ax25 bc tnc0


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ax25 bcinterval [<seconds>]                 Default: 0 (disabled)
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Display or set the time interval between beacon broadcasts.

On display both the interval and the countdown values are shown.

>> Example:  ax25 bcinterval 179


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ax25 bctext ["<broadcast_text"]
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Display or set the text to be sent for beacon broadcast messages.

>> Example:  ax25 bctext "NS9BOB TCP/IP"


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ax25 blimit [<count>]                                 Default: 30
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Display or set the AX.25 retransmission backoff limit.  Normally
each successive AX.25 retransmission is delayed by twice the
value of the previous interval; this is called binary exponential
backoff.  When the backoff reaches the 'blimit' setting it is
held at that value.

To prevent the possibility of "congestive collapse" on a loaded
channel, 'blimit' should be set at least as high as the number of
stations sharing the channel.  Note that this is applicable only
on actual AX.25 connections; UI-frames will never be re-
transmitted by the AX.25 layer.

>> Example:  ax25 blimit 30


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ax25 digipeat [on | off]                              Default: on
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Display or set the digipeater enable flag.

>> Example:  ax25 digipeat off


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ax25 filter  [0 | 1 | 2 | 3]            Default: 0 (no filtering)
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Display or set the logging of heard lists of source and
destination AX.25 callsigns.  This is a bitwise-OR function where
the 01 value is for source stations and the 02 value for
destination stations.  When the bit is '0', logging is enabled,
when '1' disabled.

>> Examples:  ax25 filter 0       (log sources and destinations)
              ax25 filter 1       (log destinations only)
              ax25 filter 2       (log sources only)
              ax25 filter 3       (no logging)


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ax25 flush
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Clear the AX.25 "heard" list (see 'ax25 heard').


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ax25 heard
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Display the AX.25 "heard" list.  For each interface that is
configured to use AX.25, a list of all callsigns heard through
that interface is shown, along with a count of the number of
packets heard from each station and the interval, in hr:min:sec
format, since each station was last heard.

The local station always appears first in the listing; the packet
count actually reflects the number of packets transmitted.  This
entry is always present even if no packets have been sent.


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ax25 hearddest <interface>
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Displays the destination list; i.e. the addressed-to stations.
The display shows latest times of transmission to stations,
together with the times that the stations replied.

This gives a good reference to see if a station is reachable and
responding.

>> Example:  ax25 hearddest tnc0


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ax25 irtt [<millisecs>]                             Default: 5000
_________________________________________________________________
Display or set the initial value of smoothed round trip time to
be used when a new AX.25 connection is created.  The old T1 value
is now taken to be 2*irtt and is variable.  The actual round trip
time will be learned by measurement once the connection has been
established.

>> Example:  ax25 irtt 2500


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ax25 kick <&AXB>
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Force a retransmission on the specified AX.25 control block.
Control block numbers are obtained with the 'ax25 status'
command.

>> Example:  ax25 kick 000000000


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ax25 maxframe [<window_size>]                          Default: 1
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Establish the maximum number of frames that will be allowed to
remain unacknowledged at one time on new AX.25 connections.  This
number cannot be greater than 7.

For best performance on a half-duplex radio channel, maxframe
should always be set to 1.  The reasons are explained in the
paper "Link Level Protocols Revisited" by Brian Lloyd and Phil
Karn, which appeared in the proceedings of the ARRL 5th Computer
Networking Conference in 1986.

>> Example:  ax25 maxframe 1


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ax25 mycall [<callsign>]
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Display or set the local callsign for AX.25 packets.  This also
defines the callsign of the NET/ROM node.

***** This command must be given before any 'attach' commands
***** using AX.25 mode are given.

>> Example:  ax25 mycall NS9BOB-5

[N.B.  The 'ax25 mycall' command identifies your call to NOS, but
does not set the TNC 'MYCALL' parameter.  You must therefore set
up the TNC with your call before using NOS.  You can do this by
using the TNC command 'MYCALL', or by using the NOS 'comm'
command].


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ax25 paclen [<bytes>]                                Default: 256
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Display or set the maximum size of I-fields on new AX.25
connections.  If IP datagrams or fragments larger than this are
transmitted, they will be transparently fragmented at the AX.25
level, sent as a series of I-frames, and reassembled back into a
complete IP datagram or fragment at the other end of the link.

To have any effect on IP datagrams, this parameter should be less
than or equal to the MTU of the associated interface.

The more data you put into an AX.25 I-frame, the smaller the
AX.25 headers are in relation to the total frame size.  In other
words, by increasing 'paclen', you lower the AX.25 protocol
overhead.

Also, large data packets reduce the overhead of keying up a
transmitter, and this can be an important factor with higher
speed modems.  On the other hand, large frames make bigger
targets for noise and interference.  Each link has an optimum
value of 'paclen' that is best discovered by experiment.

Another thing to remember when setting 'paclen' is that the AX.25
version 2.0 specification limits it to 256 bytes.  Although NOS
can handle much larger values, some other AX.25 implementations
(including digipeaters) can not, and this may cause inter-
operability problems.  Even NOS may have trouble with certain
KISS TNCs because of fixed-size buffers.  The original KISS TNC
code for the TNC-2 by K3MC can handle frames limited in size only
by the RAM in the TNC, but some other KISS TNCs cannot.


>> Example:  ax25 paclen 256


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ax25 pthresh [<bytes>]                               Default: 128
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Display or set the poll threshold to be used for new AX.25
Version 2 connections.  The poll threshold controls
retransmission behavior as follows.  If the oldest unacknowledged
I-frame size is less than the poll threshold, it will be sent
with the poll (P) bit set if a timeout occurs.  If the oldest
unacked I-frame size is equal to or greater than the threshold,
then an RR- or RNR-frame, as appropriate, will be sent with the
poll bit set if a timeout occurs.

The idea behind the poll threshold is that the extra time needed
to send a "small" I-frame instead of a supervisory frame when
polling after a timeout is small, and since there's a good chance
the I-frame will have to be sent anyway (i.e. if it were lost
previously) then you might as well send it as the poll.  But if
the I-frame is large, send a supervisory (RR/RNR) poll instead to
determine first if retransmitting the oldest unacknowledged I-
frame is necessary; the timeout might have been caused by a lost
acknowledgement.  This is obviously a tradeoff, so experiment
with the poll threshold setting.  The default is 128 bytes, one
half the default value of 'paclen'.

>> Example:  ax25 pthresh 128


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ax25 reset <&AXB>
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Delete the AX.25 connection control block at the specified
address (which can be found with the 'ax25 status' command).

>> Example:  ax25 reset 0000000


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ax25 retry [<count>]                                  Default: 10
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Limit the number of successive unsuccessful retransmission
attempts on new AX.25 connections.  If this limit is exceeded,
link re-establishment is attempted.  If this fails retry times,
then the connection is abandoned and all queued data is deleted.

>> Example:  ax25 retry 10


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ax25 route
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Display the AX.25 routing table that specifies the digipeaters to
be used in reaching a given station.


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ax25 route add <target_callsign> [digi_callsign ... ]
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Add an entry to the AX.25 routing table.  Note that 'v' (via) is
not used with the digipeater callsigns.

An automatic 'ax25 route add' is executed if digipeaters are
specified in an AX.25 connect command, or if a connection is
received from a remote station via digipeaters.  Such automatic
routing table entries won't override locally created entries,
however.

>> Example:  ax25 route add NS9KEN-5 AX9LIZ-0 AX9JIM-1


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ax25 route drop <target_callsign>
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Drop an entry from the AX.25 routing table.

>> Example:  ax25 route drop NS9KEN-5


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ax25 route mode <target_callsign> [vc|datagram|interface]
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>> Example:  ax25 route mode WW9XYZ-5 vc


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ax25 status [<&AXB>]
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Without an argument, display a one-line summary of each AX.25
control block.  If the address of a particular control block is
specified, the contents of that control block are displayed in
more detail.  Note that the send queue units are frames, while
the receive queue units are bytes.

>> Example:  ax25 status 0000000


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ax25 t3 [<millisecs>]                                  Default: 0
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Display or set the AX.25 idle "keep alive" timer T3.

>> Example:  ax25 t3 65000


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ax25 t4 [<seconds>]                                   Default:300
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Display or set the AX.25 link redundancy timer T4.

>> Example:  ax25 t4 300


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ax25 timertype [original | linear | exponential]
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Display or set the AX.25 timer backoff mode.  In an amateur radio
environment, linear backoff is essential.

>> Example:  ax25 timertype linear


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ax25 version [1|2]                                     Default: 2
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Display or set the version of the AX.25 protocol to attempt to
use on new connections.  Version 2 uses the poll/final bits.

>> Example:  ax25 version 2


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ax25 window [<bytes>]                               Default: 2048
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Display or set the number of bytes that can be pending on an
AX.25 receive queue beyond which I-frames will be answered with
RNR (Receiver Not Ready) responses.

This presently applies only to suspended interactive AX.25
sessions, since incoming I-frames containing network (IP,
NET/ROM) packets are always processed immediately and are not
placed on the receive queue.  However, when an AX.25 connection
carries both interactive and network packet traffic, an RNR
generated because of backlogged interactive traffic will also
prevent network packet traffic from being sent.

>> Example:  ax25 window 2048