On 09/19/2012 07:39 AM, McKown, John wrote:
ftp does not go through as many transitions. Basically, there is an IP
connection to a server which write directly to a file. The only encode/decode
is if you do an ASCII translation. With TSO IND$FILE, you must encode and
decode all your data into a 3270 data stream. Which, due to TSO, is half duplex
(like the old walkie talkies, only one side talks at a time). You then IP
connect your TN3270 emulator to a TN3270 server which encodes the 3270 data
stream. Also, then IND$FILE transfer is limited to the size of your TSO screen.
I.e. send one screen of encoded data (at most 80x24, or 1920, bytes for a -2;
27*132==3564 for a -5); wait and decode the response (protocol overhead); wash,
rinse, repeat until all data is transferred. The protocol and data translation
(if any) overhead on ftp is much less.
The above is just my SWAG based on some knowledge of how IND$FILE works
internally.
TSO File Transfer was also slow when TN3270 and IP were out of the
picture and you just had a coax-attached PC 3270 emulator with only
VTAM, 3270 protocol, and 3274 controllers involved. Considering the age
of IND$FILE on MVS, there is probably minimal buffering used for
reading/writing the file under TSO on MVS. Depending on DASD block size
and latency times, Just failing to adequately buffer the DASD file I/O
could easily degrade the throughput by an order of magnitude. That,
plus the inefficiencies of trying to kludge arbitrary data into
half-duplex 3270 data-stream protocol, which was designed and optimized
for sending formatted text fields, is probably sufficient to explain why
this has never been a good way to transfer data files unless they were
very small.
Given the typical product and product-version unique, tedious, and
therefore error-prone methods for specifying IND$FILE file attributes
and file sizes on various 3270 emulators, I also found that even for
transferring small files with non-standard attributes, success was
easier and sooner obtained with FTP and MVS-consistent "quote site"
attribute overrides than trying to re-discover how to specify the
correct attributes through the unique GUI interfaces of some emulator
product or to decipher/modify existing transfer profiles unique to a
specific PC instance of that product. I ceased to use IND$FILE except
when no other option for file transfer was available and the experience
in those few cases was frequently unpleasant by comparison.
--
Joel C. Ewing, Bentonville, AR jcew...@acm.org
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