The first attempt to avoid collisions was through the use of the DWAIT
and RESPTIME timers. DWAIT forced the TNC to delay the transmission
of any packet except for digipeated frames by the time selected. This
fixed timer helped, but packet was still plagued by collisions. The
RESPTIME was added to help with large file transfers. Still, more
needed to be done to reduce collisions.
Another attempt to reduce collisions was the introduction of AX.25
version 2 protocol. On VHF packet, most everyone uses version 2 which
is controlled by the AX25L2V2 command (default ON). On VHF this
helps, but some users on HF packet are turning this command OFF.
An exponentially distributed random wait method was proposed by Phil
Karn (KA9Q) called P-persistent CSMA. When the command PPERSIST is ON
(default) the PK-232 uses the number set in PPERSIST and the time
value set by the SLOTTIME command to more randomly distribute the
transmit wait time. This is more efficient than using the DWAIT time.
As a further attempt to improve packet performance, Eric Gustafson
(N7CL) proposed giving priority to acknowledgment packets (ACKs).
This protocol is controlled by the ACKPRIOR command which currently
defaults OFF. Check with the experienced packet users in your area
and find out if they are using priority acknowledge or have changed
any other parameters.
4.5.6 CHECK and RELINK
If someone connects to you and then turns his TNC off, you would
probably not want to stay connected to the station forever. The CHECK
timer determines the amount of time the PK-232 will wait before
testing the link if no data has been sent or received.
The RELINK command sets what happens after the CHECK timer has expired.
If RELINK is OFF, the PK-232 will change to the Disconnected state.
If ON, the PK-232 will attempt to reconnect to the distant station.
4.6 Multiple Connection Operation
Since packet radio allows many stations to share the same channel,
many QSOs can be going on at the same time. Because packet radio has
this channel sharing capability, there is no reason you cannot
converse with more than one station at the same time. Being connected
to multiple stations at once is a powerful feature of your PK-232.
4.6.1 Multiple Connection Description
The PK-232 offers ten logical channels, each of which can support one
conversation. In effect, multiple connect operation is much like a
ten-line telephone with automatic "hold". When you are connected to
multiple stations you will automatically receive everything sent TO
you. You must select the proper channel (in effect push the proper
line button on the telephone) to send data to a particular station.
If you are using an AEA PAKRATT program, this is described in the
program manual. If you are using a terminal, the rest of this section
will describe how to set up the PK-232 for multiple connections.
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