COMMANDS
38
PBPerson
ON | OFF
V 2.85
default OFF
All Units
PBBS
When OFF, the personal mailbox will allow messages to be sent to any callsign. When ON only
messages addressed to the MYCALL or MYPBBS callsign will be accepted.
See also: mycall, mypbbs, pbbs
PErm
immediate
All Units
This command causes any parameters changed since the last PERM command to be made "perma-
nent"; all values are burned into the EEPROM. As this process can not be undone by turning the
unit off, care should be taken to see that the correct values have been selected. The EEPROM chip
can be PERMed a minimum of 1,000 times, typically over 10,000 times. The RESTORE D command
or a Hard Reset (as described in the Installation Manual) will reinstall the factory default parame-
ters. If using the optional Battery Backup or SmartWatch all changed parameters are backed up
immediately and PERM is not necessary.
See also: restore
PERSist
n
(n = 0 – 255)
V 2.7
default 63
KPC-1
/
KPC-2
/
KPC-2400
Packet/TCP-IP
default 192/63
KAM
Packet/TCP-IP
default 63/63
KPC-4
Packet/TCP-IP
n is used to determine if a packet will be sent after SLOTTIME expires. For example, 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 1 in 4. (Actually the probability is PERSIST plus 1 di-
vided 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 re-
peated until the TNC gains channel access and sends its packet of information.
The algorithm used to determine whether or not to transmit using the PERSIST/SLOTTIME method
has been show 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 thru put
under most channel conditions. Making SLOTTIME smaller will cause the TNC to generate the ran-
dom number more frequently, whereas raising the PERSIST value will give a better chance (im-
prove the odds) of transmitting the data. Through careful choice of these values, it is possible to
improve data thru put while at the same time permitting shared channel usage by other Packet
stations. The persistence algorithm has been added on top of the DWAIT algorithm.
See also: slottime
