From: john@starfire.MN.ORG (John Lind)
Newsgroups: comp.protocols.ppp
Subject: Re: Seeking info on PC hardware requirements for high-speed PPP
Summary: big trouble
Keywords: PPP PC 486
Date: 14 Aug 92 02:56:32 GMT
Organization: Starfire Consulting Services, Mpls., MN

In article <kemp.713460871@convex.convex.com>, kemp@convex.com (Phil Kemp) writes:
> In <1992Aug7.224514.12152@parc.xerox.com> jellinek@Xerox.com (Herb Jellinek) writes:
> 
> 
> >Hi,

Well, I was going to include quotes from the original article, but I ran
into a line-length problem.  Not to pick on you, Herb, but how can a
fellow who is a Unix-type person treat news like a word processor?

Anyway, as I understand it, you have made incompatible decisions.  SLIP
and PPP are inherently ASYNC protocols, but you have picked a SYNC
physical transport system.  Boom!  Barking up the wrong tree.

Though nothing enforces this approach, the general way things have been
done is that sync connections tend to be dedicated, while async connections
are dial-up.  There are exceptions, and most of us have seen or own 2400bps
and 1200bps modems that will do synchronous over dial-up, or which will
do async over leased lines, but in the really high-speed world, the
SYNC/dedicated ASYNC/dial grouping is essentially the unwritten law.
Since you are talking CSU/DSU, you aren't talking async or dialup at all.

Now that we move into the WAN world, the separations become even
stronger, though there is no inherent technical reasons for them.
Let me state that more clearly.  It is not a trivial change.  There
are inherent technical reasons why an async protocol won't work on
a sync line and vice versa, but there are no inherent technical reasons
that a given protocol had to be implemented for a given serial link
type -- they just tended to follow the modem industry lead: dialup
is async (and intermittant connectivity), dedicated is sync (and
fully connected).  With your synchronous dedicated line, there ISN'T
anything quite like PPP or SLIP that will use it, without putting a
stat mux or some similarly ridiculously complex and hardware intensive
solution on both ends.

You don't need PPP and you don't need SLIP to use that line.  You need
bridge/router software/hardware.  Either that or scrap the synchronous
connection and go dial dialup V.42bis.  And, in case you haven't
looked at bridge/routers lately, they have a lot more horses under the
hood than your 486 box in most cases, and sophisticated dedicated
hardware to assist in their complex and time-critical job besides.

You can get bridge/router cards to plug into your 486 PC/ISA/EISA bus,
I hear, but I don't know of them and I haven't used any.  These cards
pretty much just use the bus and enclosure for cooling and power.
You would STILL need some sort of network connection to talk to the
bridge/router.

Let's draw a picture:

Ethernet at work: ~============o============o===============oT
Cable taps*:                   |            |               |
	 		     -----        -----           -----
MAU/AUI*:                    |MAU|        |MAU|           |MAU|
			     -----        -----           -----
Transciever cables*:           |            |               |
                       --------------  -----------------  ----------
		       | Bridge or  |  | HOST 1        |  | HOST 2 |
		       | Router or  |  | w/SLIP or PPP |  ----------
		       | both       |  -----------------
		       --------------    |  Async line/standard port      
	V.35 or RS232 sync line |      ---------
			   ---------   | Async |
			   |CSU/DSU|   | modem |
			   ---------   ---------
	leased/dedicated line ||          ||     PSTN (Public Switched
			      ||          ~~     Telephone Network)
			   ---------      ||     I.e. dialup
                           |CSU/DSU|   ---------
			   ---------   | Async |
	V.35 or RS232 sync line |      | modem |
		       -------------   ---------
		       | Bridge/   |     | Async line
		       | Router    |   -----------------------------------
		       -------------   | Home System 1 running TCP/UDP   |
	Transciever cable* |           | via SLIP or PPP routing through |
			 -----         | HOST 1 for all other access     |
	MAU/AUI*	 |AUI|         -----------------------------------
			 -----
	Tap*		   |
	Ethernet at home  To====oT
	Tap*                    |
			      -----
	MAU/AUI*	      |MAU|
			      -----
	Transciever cable*      |
	      ---------------------------------------
	      | Home System 2 w/ethernet controller |
	      | for TCP/IP communicating as a peer  |
	      | with HOST 1, HOST 2, and other IP   |
	      | devices locally and at work.        |
	      ---------------------------------------

* These items may be bundled into the network device, almost certainly
  for 10baseT, and often for ThinNet.  For 10baseT though, you need
  a hub.  Tradeoffs, always tradeoffs!

For Home System 2, the WAN link is "transparent" if the Bridge/Routers
are strictly bridges, or routed if they are routers.  Some savings are
clearly possible if the work network already has a router or bridge
with a serial line/WAN port available.

We just installed a setup much like "Home System 2" for a client,
except that they also had a LAT/IP gateway on the "home" side, so the
local LAN had three devices rather than the trivial two shown here.

I wish you all the luck in the world.  If you find what you are looking
for, such information would be very enlightening to me, obviously.
-- 
		   John Lind, Starfire Consulting Services
E-mail: john@starfire.MN.ORG		USnail: PO Box 17247, Mpls MN  55417