Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!rutgers!bellcore!faline!thumper!ulysses!smb
From: smb@ulysses.homer.nj.att.com (Steven Bellovin)
Newsgroups: comp.dcom.modems
Subject: Re: 'g' & packet sizes & extensions
Message-ID: <10581@ulysses.homer.nj.att.com>
Date: 6 Sep 88 18:17:03 GMT
References: <7272@bigtex.uucp> <10500003@osiris.cso.uiuc.edu> <6452@chinet.UUCP> <169@arnold.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 23

In article <169@arnold.UUCP>, dave@arnold.UUCP (Dave Arnold) writes:
> 
> I really doubt the 'd' protocol has goals much different than 'x' or
> 'e' or 't'.  Seems like all these could have been combined into one.
> One prococol for an error-free channel.  Or am I missing somehting?

Some of the protocols we're talking about were tuned to particular
hardware environments.  The 'd' protocol relies on the ability of the
Datakit(r) VCS to propogate 0-length writes, which TCP cannot do.  Not
only that, the 0-length write is accompanied by a special control byte,
which some versions of dio require on input.  Dio also issues some
ioctl calls to the driver so that reads return on end-of-block, not
just when the user's buffer is full.  (This could be done differently
today with HDB.)  All of these considerations led Peter and I to invent
eio.  (Incidentally, eio was originally written for UNET, 3Com's
TCP/IP, and antedates 4.2bsd.) Tio was developed later, and
independently; there doesn't seem to be much need for both it and eio.
I've never heard of vio; xio was for a (rather specialized) X.25
interface available.  And I've heard rumors of a protocol that worked
via shared disks; the sender merely informed the receiver of the name
of the file to be sent.  Does anyone know any more about that?

		--Steve Bellovin