Flow Control and FIFOs (Re: Son of FAS?)

[Marco S Hyman]

In article <3821 at sixhub.UUCP> davidsen at sixhub.UUCP (bill davidsen) writes:
 >   Now, on the XOFF, any system with a FIFO may well keep right on
 > sending after the XOFF, and I think there's a standard which calls for
 > XOFF 1 sec before buffer full, I just can't remember where I saw it. We
 > hit this in 1978 or so when running a mainframe into an old S100 system
 > at 38.4.

Time for the back of the envelope. At 38.4 Kbps speaking async 1 second
is ~ 3840 characters.  That's a lot of buffer space destined to never be
used. Last week, using a 256 byte buffer I had to change the "flow off"
point from 2/3 full to 1/2 full when speaking to a 3b2/600 at 19.2 Kbps.
As the 3b2 got busy I was dropping characters -- about 10-20 implying the
buffer should have been 80-100 bytes or about 50 milliseconds worth. Going
to 64 milliseconds worth of buffering did the job no matter how bad the
load. Note: a VAX 780 running VMS (ugh!) had no problems shutting down
within the original 32 millisecond of buffering.

-- 
// marc
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