Kantronics MT1200, Руководство пользователя

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address field as well as the data field and display the packet as specified by other
commands such as MONITOR.
➔ When PASSALL is OFF, packets will be displayed only if the CRC (error checking) is
correct and as specified by other commands such as MONITOR.
PERSIST n (n = 0 - 255)
default 63
This command, used with SLOTTIME, implements an algorithm for channel access 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.
Making SLOTTIME smaller will cause the TNC to generate the random number more
frequently, whereas raising the PERSIST value will give a better chance (improve the
odds) of transmitting the data. Through careful choice of these values, it is possible to
improve data throughput 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
PID {ON | OFF}
default OFF
When OFF, only those packets with a protocol ID of $F0 (pure AX.25) are displayed.
When ON, all packets are displayed. Some of the information in non-AX.25 packets (for
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