Timewave PK-900, Operating Manual

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The TRIES counter keeps track of the retries that have occurred on the
current packet.
4.5.4 PACLEN and MAXFRAME
Packets will be sent either when the <Enter> key is pressed or when
the maximum packet size is exceeded. The maximum packet size is set
by the PACLEN command which defaults to 128 characters. When large
amounts of data need to be sent, this value can be increased to 256.
When conditions are poor or the channel is crowded as on HF packet,
this value should be reduced to 64 or less.
The packet protocol allows more than one frame to be sent in a single
transmission. The default is set to 4 by the MAXFRAME command. When
conditions are good up to 7 frames can be sent to speed data transfer.
When conditions are poor or the channel is crowded, MAXFRAME should be
reduced to only 1 frame.
4.5.5 Reducing Errors through Collision Avoidance
If every packet station could hear every other station, there would be
very few "collisions" due to stations transmitting at the same time.
Since packet operates over radio, there are often many stations on the
same frequency that cannot hear each other. Digipeaters and network
nodes allow these stations to communicate with each other, but this
increases the chances of collisions.
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-900 uses the number set in PERSIST 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 experienced packet users in your area and
find out if they are using priority acknowledge or have changed any
other packet 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-900 will wait before
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