Page 30 of 101
DWG ID: 181-0101-00A
Date: 2003-09-26
require more time to be transmitted, more time to be repeated by the digipeater, and so on
down the line. The FRACK timer begins when the packet has been sent and is suspended
when data carrier from the radio is present, or when your station is transmitting.
8.11
Retries in AX.25 Level 2, Version 1 vs. Version 2
The way retries are accomplished depends on AX25L2V2 being OFF or ON. If a packet
is transmitted to a connected station, and an acknowledgement is not received back, the
entire packet is retransmitted (with the same frame number) up to the number of tries
specified by the RETRIES command, until an acknowledgement is received. If
acknowledgement is still not received, a disconnect sequence is started, up to the number
of RETRIES again. If there is still no response from the other station, the
unacknowledged packet is discarded. In level 1 type responses, single pairs of angle
brackets are used (such as <rr0>).
Under version 2 (AX25L2V2 ON), when an acknowledgement has not been returned, a
POLL only is sent (not the entire packet), up to the number of times specified by
RETRIES. In level 2 type responses, two pairs of angle brackets are use (such as
<<rr0>>).
8.12
Convers Mode vs. Transparent Mode
In the Convers Mode special control characters are still recognized. They are used to edit
typed data before transmitting it, to pass through special characters as data to another
station, or to cause a packet to be transmitted.
Transparent Mode was designed for sending files, whether ASCII data files or program
files. Special characters (other than TRFLOW and TXFLOW, when ON) have no
meaning to the TNC in transparent mode, they are just data characters to be put in a
packet and sent to the radio.
In Transparent Mode, the PACTIME command defines when packets are transmitted.
There is no MONITOR function while in TRANSPARENT mode. Only data from a
connected station can be received.
8.12.1
Exiting Transparent Mode
Since Transparent Mode allows the sending of all characters, only a special sequence of
characters or a modem break will exit Transparent Mode. The command called
CMDTIME sets a timing of character entry that will allow the use of the COMMAND
character in the special character sequence. Three COMMAND (<Ctrl+C>) characters
must be entered within CMDTIME of each other, with at least one CMDTIME before
and after the special sequence.
Some terminal programs can send a MODEM BREAK signal, which toggles the TXD
line for a specific period of time that is longer than a standard character bit time. This will
