Path: utzoo!bnr-vpa!bnr-fos!tpc
From: tpc@bnr-fos.UUCP (Tom Chmara)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Reliable datagram service available? (SUMMARY)
Summary: look at VMTP, XTP
Keywords: datagram UDP IP
Message-ID: <559@bnr-fos.UUCP>
Date: 8 Jun 89 17:08:31 GMT
References: <526@bnr-fos.UUCP>
Reply-To: tpc@bnr-fos.UUCP (Tom Chmara)
Organization: Bell-Northern Research, Ottawa, Canada
Lines: 93

In article <526@bnr-fos.UUCP> I asked...

>Does anyone know of any
>	a) free
>	b) $$
>software which implements reliable datagram service, something like the
>	SOCK_SEQPACKET
>(sequenced, reliable, two-way connection-based byte stream for fixed-length
> datagram)
>described in the literature?

"DID WE GET LETTERS!?!"
To summarize:
	- I asked for the wrong thing, though many people figured out what
	  it was I wanted vs asked for.  As Craig Partridge & jqj@hogg
	  were so kind as to point out, with admirable restraint..
	  (jqj's words):

		"You asked about both RDP and sequenced packet protocols.
		4.3BSD supports a sequenced packet protocol, SPP, in the
		XNS domain.  A reliable SPP carries almost all of the baggage
		(except fragmentation/reassembly) that a TCP stream does i.e.
		is just as expensive.  All it does is *in addition to providing
		a stream* provides information to the client on packet
		boundaries.  Not what you want."

	  What I WANTED was reliable datagrams.  (Craig Partridge HAS a
	  sequenced packet protocol:  RDP, for those who might want it; contact
	  him at craig@nnsc.nsf.net).

	- I heard about TWO reliable datagram protocols.  One is eXpress
	  Transfer Protocol (XTP).  Rex Buddenberg (budden@manta.nosc.mil)
	  described it as follows:

		"Not exactly free, and not exactly here yet either...but.
		Reliable datagram service isn't as easy as it sounds at first
		encounter.  First, consider how TCP handles things:
			<description left out>
		Note that you've burned up 9 packets in order to get one packet
		through the system.  Further, the data packet is the fourth one
		in line -- if latency is a concern (and in tactical applications
		it most definitely is), then you've eaten up a lot of overhead
		before you get real performance.

		What we are currently latched onto is eXpress Transfer Protocol.
		XTP allows the connection open, the data and the connection
		close to all go in the very first packet.  So you get out with
		a grand total of 3 packets for guaranteed delivery; and the
		data goes in packet #1 now.

		XTP is being build by Protocol Engines Inc in Santa Barbara.
		They intend to embed it in a chipset in a year or so.  In the
		meantime, some beta sites are running C versions.  If you are
		looking for a 'today' answer this isn't it, but next year..."

	 I heard from many people about the second reliable datagram protocol:
	 Guy Middleton won with being first here; jqj@hogg, dave crocker
	 (dcrocker@ahwahnee.stanford.edu) also replied.  Sorry if I missed
	 anyone...  The protocol is VMTP ( Versatile Message Transport
	 Protocol) and is described by RFC 1045.
	
	 The abstract for RFC 1045 describes VMTP as
		"a transport protocol specifically designed
		to support the transaction model of communication, as
		exemplified by remote procedure call (RPC).  The full function
		of VMTP, including support for security, real-time, asynchronous
		message exchanges, streaming, multicast and idempotency,
		provides a rich selection to the VMTP user level.
		Subsettability allows the VMTP module for particular
		clients and servers to be specialized and simplified to the
		services actually required."
	
	VMTP is layered atop IP; i.e. is a peer protocol to UDP and TCP.  The
	VMTP README file for the second release notes that VMTP
		"is available for "Sun-3, Sun-4, Vax, and DEC mips architecture
		machines"

	VMTP is available from Stanford University Distributed Systems Group.
	If you wish to be added to the VMTP mailing list, drop a line to
	vmtp-ip-request@gregorio.stanford.edu.  Postings to the mailing list
	are sent to vmtp-ip@gregorio.stanford.edu.
	I do not know any details regarding licensing for educational or
	commercial use.

Thanks to all who responded; if I've missed your name in the above credits,
please accept my abject apologies.  Response to my question was as always
quick, insightful, and clear.  Thanks again.
	---tpc---
-- 
I am sole owner of the above opinions. Licensing inquiries welcome.
------------------------------------------------------------------------
Tom Chmara			UUCP:  ..utgpu!bnr-vpa!bnr-fos!tpc
BNR Ltd.  			BITNET: TPC@BNR.CA