Path: utzoo!attcan!uunet!husc6!purdue!decwrl!ucbvax!Philip
From: Philip Prindeville@UDEL.EDU, philipp@larry.mcrcim.mcgill.EDU
Newsgroups: comp.protocols.tcp-ip.ibmpc
Subject: Re:  "host-based" vs. "front-end-processor" PC network interfaces
Message-ID: <8805132056.AA13505@Larry.McRCIM.McGill.EDU>
Date: 13 May 88 20:56:06 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 63


	Date: 13 May 88 01:34:23 GMT
	From: Chuck Kollars <pyramid!leadsv!excelan!chuck@decwrl.dec.com>
	Subject: "host-based" vs. "front-end-processor" PC network interfaces
	To: pcip@louie.udel.edu
	
	[ ... ]
	Some potential advantages of the Front End Processor architecture:
	 o  offload packet handling from host CPU 
	 o  reduce host memory requirements 
	 o  larger data holding buffers and sliding window sizes 
	 o  shorter latency between received packet and acknowledgement
	 o  partially offload keystroke processing 
	 o  many simultaneous connections 

A major drawback is that you can't support multihomed hosts as easily.
About the only thing a board-resident IP can do is perform checksumming.
No reason you can't support multiple sessions with a host-resident TCP/IP.
	
	Some of these advantages are most relevant to multiprocessor (ex:

I think you meant "multiprocessing" (or multitasking), not "multiprocessor".

	OS/2) or multiuser (ex: Xenix) systems.  Others are especially
	relevant to systems with memory address space restrictions (ex: DOS).
	
	The interface to the transport layer is a convenient place for 
	separating host and onboard portions.  Applications using an 
	interface like SOCK_STREAM sockets can pass their data to the network 
	with simple read() and write() calls.  Separation between the host 
	and onboard portions is especially clean for "stream" or "pipeline" 
	style transport layers (ex:TCP, named pipes).  

You will have to explain to me why streams are more convenient than
datagrams.  I would have thought it would be easier with datagrams, since
there is even less state to maintain between transactions.

	While Excelan did not invent the Front End Processor approach and does

(Not by a long-shot.  Ever hear of the Honeywell H16? [so called "Susie"])

	not restrict its product line to FEP configurations, "Excelan style" 
	is sometimes used to mean "outboard" or "onboard" protocols.

	[ ... plug deleted ... ]
	
	"Host-based" vs. "front-end-processor" has been discussed to death
	for years on the network, in the literature, and elsewhere.  This

That isn't to say that new approaches aren't being developed.  Dave
Clark or MIT-LCS (the Internet Architect) is working on a idea that merges
off-host processing with named pipes (he calles it "named buffers").  It
is an interesting concept, and could well appear in implementations fairly
soon (if only in labs)...

	posting is intended to provide a brief introduction to the topic for
	people who are new to LAN's, not to rekindle old religious wars.  It 
	was prompted by peripheral references to the FEP vs. Host-Based issue 
	in some recent articles in this newsgroup:

And I thought it was to sell Excelan cards... :-)

-Philip