Kantronics KPC-9612 Plus, Руководство пользователя

Страница: 280 / 348

PBREVERS {ON | OFF}
default ON
When ON, the TNC PBBS will request a reverse forward from another BBS after
it has finished forwarding any mail to the other BBS. This does not affect the
ability of another BBS to reverse forward from your PBBS, but only affects the
action taken by the TNC after it has initiated a forward (PBFORWRD com-
mand). Note: Your PBBS will not forward or reverse forward unless HTEXT is
set.
See also: pbforwrd
PERSIST n (n = 0 - 255)
Multi-Port
default 63/63
This command, used with SLOTTIME, implements an algorithm for channel ac-
cess to send packets. The algorithm used to determine whether or not to transmit
using the PERSIST/SLOTTIME method has been shown to be considerably more
efficient than the DWAIT method used by most standard AX.25 packet stations.
The result of using the persistence algorithm is increased throughput under most
channel conditions.
The value of “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 divided 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 repeated until the TNC gains channel access and sends
its packet of information.
Command Reference TNC Commands
User’s Guide 264 KPC-9612 Plus v 8.2