Path: utzoo!attcan!uunet!zaphod.mps.ohio-state.edu!usc!ucsd!ucbvax!FTP.COM!jbvb
From: jbvb@FTP.COM (James B. Van Bokkelen)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Reliable Datagram ??? Protocols
Message-ID: <9010251954.AA15469@ftp.com>
Date: 25 Oct 90 19:54:21 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: jbvb@ftp.com
Organization: The Internet
Lines: 29

If you can fit your entire message in one MAC-layer packet, and you only
have one, a formal connection can be replaced by server idempotency.  However,
if you have more than one message (or they are larger than one MAC-layer
packet), consider the following:

Dir	Flags		Data.

 <-	SYN		Transaction 1 request.
 ->	SYN ACK		Transaction 1 response.
 <-	ACK FIN		Transaction 2 request.
 ->	ACK FIN		Transaction 2 response.
 <-	ACK

Two transactions, five packets, perfectly legal TCP, and the server
doesn't have to be idempotent.  Four is the absolute minimum with UDP if
the server is idempotent.  I am not contending that any existing TCP API
will allow this streamlined an exchange, or that all TCPs can handle data
with the SYN (almost all can handle data with the FIN).  However, I will
argue that work in this direction offers more bang per buck than
developing both the sophisticated API and a new protocol to go under it.

One might criticize my scenario on the grounds that transaction processing
might delay things enough to cause retransmissions.  However, the same problem
afflicts any transport in this situation.  If processing time is predictable,
the API must allow setting initial timeout values.  If not, the net suffers
regardless of the API.

James B. VanBokkelen		26 Princess St., Wakefield, MA  01880
FTP Software Inc.		voice: (617) 246-0900  fax: (617) 246-0901