UUCP performance
ITEM: RS4000000967
**************> QUESTION level 1 --> level 2 SPECIALIST <**************
Hello, folks.
I have a question about UUCP performance.
My customer connected 2 RS/6000s with UUCP(see the following figer).
+---------+ * * +---------+
| RS/6000 |---. modem .---/\/\/\/---. modem .---| RS/6000 |
+---------+ remote +---------+
* Two modems supports 28.8kbps communication.
He executed file transfer between two machines.
The thruput of file-transfer was about 9600 bps.
And then he re-connected RS/6000s by SLIP.
The file transfer rate of ftp was higher than UUCP (He said it was near
28.8kbps).
He thinks UUCP's transfer-rate is too late. He checked
/etc/uucp/Systems
and /etc/uucp/Devices. He found a bound rate was set 38400 bps on
those files( of course, a bound rate of tty's was also set 38400 ).
He had heard that the performance of UUCP was'nt good on AIX.
So, he thought three hypothesises.
1) There are some defects in UUCP settings. He might miss important
parameters.
2) There is a limitation for UUCP file transfer on AIX.
===
On another UNIX, there is no limitation.
3) The maxium file transfer rate is defined because of UUCP spec.
Are there any answer for the above hypothesises ?
If not, could you tell me correct answer?
Thanks and Regards.
************** ANSWER level 2 -- level 1 SPECIALIST **************
==== THIS TEXT HAS BEEN ENTERED BY IBM IN USA
==== ASGN: BUNLOEUR AT WTSCPOK ================= DATE:960819
TIME:0830
Received by Austin ITSC and assigned to AIXOPSYS.
Your question has been received, and assigned to a specialist. Please
wait for a reply. Thank you.
************** ANSWER level 2 -- level 1 SPECIALIST **************
==== THIS TEXT HAS BEEN ENTERED BY IBM IN USA
==== RESP: AIXOPSYS AT WTSCPOK ================= DATE:960819
TIME:1754
Response:
I shall attempt to answer your 3 questions with one answer that will
hopefully explain why UUCP performance can be quite slow. First,
there is not one "uucp" protocol. UUCP definitions have several
protocols. AIX supports g, e, t, and x protocols and there are
several other UUCP protocols that we don't support. For ALL UUCP
implementations, the default protocol is g.
The g protocol defined that the sender sends 64 bytes and then
waits for an acknowledgement from the remote before sending another
64 bytes... There is a lot of error checking done by UUCP and is
very slow.
e,x use larger blocks with less error checking... Somewhat faster.
t - 1K blocks, no error checking at all. Extremely fast but should
only be used over TCP/IP where TCP/IP does the error checking and
there is no need for UUCP to do more error checking.
If UUCP is slow, and BOTH systems support a common protocol other than
the default g protocol, you can improve performance by specifying the
faster protocol in the dialing systems Systems file (see examples in
/etc/uucp/Systems showing the t protocol)
AIX implementation of UUCP is the HoneyDanbur version of UUCP which is
the same you'll find on most UNIX implementations (HP, SUN, etc.) UUCP
is just a slow protocol in general... You can improve performance by
using a faster protocol, but with the strict rules of the 'g' protocol
that is used by default (send 64 bytes, wait for acknowledgement, send
another 64, etc.) there's not much that could be done to improve the
performance other than increasing the baud rate.
UUCP performance is sometimes hindered by modems that are configured
for XON/XOFF flow control... XON/XOFF characters could get into the
data stream and throw off packet checksums causing packets to be
retransmitted several times (UUCP ASSERT ERROR would be logged).
Another thing that sometimes causes problems is if one of the two
modems but not both is doing "uucp spoofing" in which the modem is
intelligent enough to determine that the transfer of data is a uucp
transfer and tries to spoof the remote end by sending acknowledgements
for the packets instead of letting the system do it... Very few modems
have this capability, so it's not a likely cause of problems.
Hope this helps out.
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