Path: utzoo!utgpu!water!watmath!clyde!att!pacbell!rtech!hoptoad!gnu
From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: comp.mail.uucp
Subject: Re: 'g' packet size
Message-ID: <5463@hoptoad.uucp>
Date: 26 Sep 88 08:01:27 GMT
References: <212@jato.Jpl.Nasa.Gov>
Organization: Grasshopper Group in San Francisco
Lines: 33

The packet size is negotiated in powers of two; it is possible to
negotiate larger packet sizes.  I have not tried it in gnuucp, but
it should work.  Last time this was mentioned though, someone
reported that old Unix uucp's would happily try to send you larger
packets, but had statically allocated buffers of the old size --
so they end up overrunning an array, writing into random memory, and
crashing.

It's not clear what effect larger packet sizes would have.  On
links that have high delay (e.g. PC Pursuit), the more data you
can shove into the pipe before stalling awaiting an ack, the better
off you are -- so since the protocol limits you to 7 packets,
making them larger is a possible way to increase thruput.  On links
with fast acks (any Telebit link, and links to quick systems), it
probably doesn't matter much.

Somebody pointed out a problem if uucico "swaps out" and you use large
packets, the tty drivers won't have room to keep all the characters.
That depends on your tty drivers of course, but regardless, if your uucico
is swapping out, your thruput is going to go to shit anyway because your
acks are delayed and the sender stops sending.

I recommend that if anyone implements larger packet sizes, you call it
the "G" protocol rather than the "g" protocol.  That is, the "G"
protocol is a "g" protocol that has no bugs around large packet sizes.
Advertise as supporting both; if you call another site with no bugs,
you'll use large packets, and if you call an older site, you'll use the
old standby 64 byte packets.

	John Gilmore
-- 
John Gilmore    {sun,pacbell,uunet,pyramid,amdahl}!hoptoad!gnu    gnu@toad.com
  there's still time to change the road you're on.  --LZ: "Stairway to Heaven"