Falcon DOS Portable Data Terminals, Advanced User'S Manual, Page: 77 / 184

Using XFER
Advanced User’s Guide
3-25
For Zmodem protocol, transmit is the default when specifying a file on the
command line. So, for example, the command
XFER /Z foo
is equivalent to
the command
XFER /Z /T foo
.
The
T
option is most useful if the
XFER_ARGS
environment variable (refer to
page 3-26
) includes the
R
command and a file is also being sent.
W
Window Size (Zmodem only) :
This option controls the use of windowing
with Zmodem protocol. By default, Zmodem is a streaming protocol, and
windowing is disabled. “Streaming” refers to the method by which Zmodem
transfers data. In streaming mode, the sender forms 1K data packets and sends
one packet after another in a continuous stream. The sender does not wait, and
does not expect, to get acknowledgments from the receiver for any of the
packets it sends. Instead, the sender assumes the file transfer is going normally
unless it gets an error indication from the receiver.
This works fine in robust, error-free environments. But the receiver can get lost
or disconnected without the sender realizing it. Windowing provides a way in
noisy environments to give some level of packet acknowledgment to Zmodem
protocol. With windowing, the sender will send up to the number of bytes
specified by the size of the window and then stop transmitting data until the
receiver acknowledges that it has received all of the packets that have been sent.
The sender then sends more packets, up to the size of the window, and so on.
Waiting for acknowledgments slows down transfer speeds, but XFER allows a
dynamic compromise between speed and robustness. XFER allows specifying
the window size with any value from
0
to
65535
. Use
W0
for streaming mode.
For a 1K window, use
W1024
. Values below
1024
are used exactly as specified
and should be the size of the transmitted packets. Values above
1024
should
be multiples of
1024
(
1024
,
2048
,
4096
, etc.). Values above
1024
that are
not multiples of
1024
are rounded up to the nearest multiple of
1024
.
If the
W
option is not included on the command line, streaming is used. If the
option is used without specifying a setting,
W0
(streaming) is used by default.
This is useful in the case where a window size is specified in the
XFER_ARGS
environment variable refer to
page 3-26
) but streaming will be used for the
current transfer session.
The last transfer option,
R
or
T
, on the command line controls whether to transmit or
receive for the session.
advuser.book Page 25 Friday, September 27, 2002 4:22 PM