Subject: RE: Current LINK snapshot available

From: "Spencer Dawkins" <[email-masked]>
Date: Mon, 25 Oct 1999 21:55:00 -0500

Steve,

OK, I'll bite. I wouldn't say a null modem cable is a CONNECTIONLESS
subnetwork - unless the RS-232 cable is LYING to you, it has two ends, and
all resources along this subnetwork are reserved for the conversation
between the two hosts, so - what did you mean by a "connection-oriented
network"?

Stepping back a tiny bit, aren't we trying to describe a path through a
subnetwork that is relatively stable (think, "call setup request", in
software), so that the use of delta encoding in RFC-1122 header compression
makes sense, because most packets are delivered in the order they were sent?
If so, reserving such a path through the use of dedicated hardware has this
property in the same way as reserving such a path via resource-reserving
software (and I didn't actually spell out RSVP on purpose!).

Spencer

> -----Original Message-----
> From:	Steve Deering [SMTP:[email-masked]]
> Sent:	Monday, October 25, 1999 6:08 PM
> To:	Phil Karn
> Cc:	[email-masked]; [email-masked];
> [email-masked]
> Subject:	Re: Current LINK snapshot available
> 
> At 10:01 AM -0700 10/22/99, Phil Karn wrote:
> >I agree that the wording may be unnecessarily restrictive, but it is
> >true that header compression is usually done over connection-oriented
> >networks.
> 
> 
> Phil,
> 
> A common use of VJ header compression is (or at least was at one time)
> on an RS-232 serial cable directly connecting two machines (i.e., no
> modems involved).  That is not a "connection-oriented network", any more
> than is an Ethernet cable with two nodes attached.
> 
> Steve
>

---

From: Steve Deering <[email-masked]>
Date: Tue, 26 Oct 1999 09:14:28 -0700

>between the two hosts, so - what did you mean by a "connection-oriented

Spencer,

A connection-oriented network is one in which potential delivery paths
exist between sources and destinations, but in order to use them, one must
first perform an explicit "connect" operation (usually by some sort of
signalling protocol).  There is usually also a corresponding "disconnect"
operation, to indicate that one is finished communicating.

A null modem cable does not require any such operations.  Sticking real
modems in there, connecting to the connection-oriented telephone network,
is what imposes the connection-oriented service model on the end devices.

Connection orientation has nothing to do with resource reservation.
You can have a connection-oriented network that does no resource
reservation (apart from the memory resources to hold the connection state
itself), such as a frame relay network with no committed data rates, and
you can have a connectionless network that supports resource reservation,
such as an IP network with RSVP.

Steve

---

From: Lloyd Wood <[email-masked]>
Date: Tue, 26 Oct 1999 18:29:48 +0100 (BST)

On Tue, 26 Oct 1999, Steve Deering wrote:
> > Mon, 25 Oct 1999 16:08:18 -0700, Steve Deering wrote:
> > > A common use of VJ header compression is (or at least was at one
> > > time) on an RS-232 serial cable directly connecting two machines
> > > (i.e., no modems involved).  That is not a "connection-oriented
> > > network", any more than is an Ethernet cable with two nodes
> > > attached.
> > 
> A null modem cable does not require any such operations.

Okay, I'll bite.

Remember hardware and software handshaking?

I'd certainly class handshaking as an explicit connect operation,
utilising a signalling protocol, that must first be carried out before
the potential delivery paths between sources and destinations become
available for use in data transmission. (in the case of the null-modem
cable, these potential delivery paths are known as "wires" or "pins".)

Well, handshaking can be carried out for the duration, too; the
absence of handshaking is the disconnect operation, just as the start
of handshaking is the connect operation. And if it's hardware
handshaking, the signalling protocol involved happens to be a
controlled wiring/voltage convention, and you're actually completing a
circuit for the duration...

Et voila, a null-modem cable is connection-oriented, because it
explicitly enables hardware handshaking in its wiring. (Maybe I should
stop wishing I had studied computer science instead of electrical
engineering.)

L.

the differences that you perceive do not lie in the networking.
those differences only lie in how you perceive the networking.

> Sticking real

<[email-masked]>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>

---

From: Steve Deering <[email-masked]>
Date: Tue, 26 Oct 1999 12:36:44 -0700

>those differences only lie in how you perceive the networking.

...or what layer you are looking at (which is one aspect of perception).
Connection orientation is a property of a service interface to a protocol
layer.  When you run TCP over IP over a dial-up modem, the TCP service is
connection-oriented, the IP service is connectionless, and the async
serial service is connection-oriented.  As you keep digging deeper, you
may find other layers that are connectionless or connection-oriented, as
you pointed out.

At the layer of concern to the compression discussion that triggered this
digression, a null modem cable is a connectionless service.

Steve

---

From: Cannara <[email-masked]>
Date: Thu, 28 Oct 1999 11:00:20 -0700

Beg to differ on the serial interface -- if you don't see DSR or CTS, you
don't send nada.  This is a long-standing hardware-based connection protocol,
called RS232 (and others, of course).  Modems have more features to add re the
different medium between them, but they themselves depend on setting up a
connection to the serial interfaces at either end.  

Alex