I have questions about the definition of printer/plotter on smit menu.
There is a item "sticky XON/XOFF flow control" on the above menu
in AIX V3.2.5.2. What is the meaning of this item ?
And what is the difference between the above item and "XON/XOFF
handshaking" in AIX V3.2.4 ?
ANSWER
Following is the comparison between XON/XOFF handshaking and
Sticky XON/XOFF flow control:
1. XON/XOFF
XON/XOFF is one type of software flow control. With this
flow control, an escape sequence for XOFF is imbedded in the
data stream when the buffer is approximately 80% full. The
XOFF signal is a "Ctrl s" and the XON signal is a "Ctrl q".
For example, when the printer's buffer reaches 80% full, an
XOFF is sent to the RISC System/6000. When this escape
sequence is interpreted by the system, no more data is sent
out to the printer port. As the printer's buffer begins to
empty out, it sends an XON signal to the RISC System/6000
which then tells the RISC System/6000 to continue sending the
remaining of the data.
2. Sticky XON/XOFF
Sticky XON/XOFF was developed to correct a defect/development
handling of multiple print jobs.
To be specific, in AIX 3.2.5, Sticky XON/XOFF was implemented
to solve the problem with printers that only send one XOFF
when their buffer is full. The printer may send this XOFF
after all the data is sent from the computer, and the computer
has closed the port and is ignoring all characters from the
printer. Thus the flow control is lost at the beginning of
the next job. Sticky XON/XOFF allows the driver to read the
XON or XOFF characters even though the port is closed. This
was done to correct some flow control problems where an XON
was sent while the port was closed but the system never saw
it.
This option was added to prevent data lost when all of the
following conditions were true:
1. No jobs in the queue.
2. Printer was taken off line (i.e. changing paper) while
no job were queue.
3. While printer is still off line, someone sends a job
to the queue.
4. Using normal XON/XOFF handshaking (not DTR)
5. The printer sends only a single XOFF when it is taken
off line.
In other words, with normal XON/XOFF the system wouldn't
recognize the XOFF when the port is not open. When Sticky
XON/XOFF is set, now the system recognizes XOFF at all times,
and the job is held until the computer comes back on.
S e a r c h - k e y w o r d s:
XON XOFF HANDSHAKING
WWQA: ITEM: RTA000086450 ITEM: RTA000086450
Dated: 03/1995 Category: ITSAI6000GE
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