W3C home > Mailing lists > Public > ietf-http-wg@w3.org > January to March 1997

Re: How to add new "protocols" ?

From: <touch@isi.edu>
Date: Wed, 19 Feb 1997 09:42:25 -0800
Message-Id: <199702191742.AA26992@ash-s.isi.edu>
To: touch@isi.edu, luigi@labinfo.iet.unipi.it
Cc: ses@tipper.oit.unc.edu, masinter@parc.xerox.com, http-wg@cuckoo.hpl.hp.com
X-Mailing-List: <http-wg@cuckoo.hpl.hp.com> archive/latest/2469
> From luigi@labinfo.iet.unipi.it Tue Feb 18 23:09:27 1997
> > > > > 	1) try  alternate protocol, and use it if it works. Cache result
> > > > Increases the connection latency. Bad in general. Besides, 
> > > 
> > > Adds an extra RTT to first connection to host
> > 
> > Only if "fails" is by NACK. Otherwise, it adds
> > a timeout, which is usually in the 2-3*RTT range, _at best_.
> It should normally fail by NACK (with the equivalent of ICMP port
> unreachable), so that's not much of an issue. Since the result of
> the probe is cached, this is not more costly than a DNS lookup.
> Besides, you can probe in parallel all (are they 2, 3, 4 ? not
> certainly a dozen) the known protocols and continue the transaction
> using the preferred one among those available.

ICMP port unreachable is a "MAY", not a "MUST".

It also can increase the load on the server, especially
when you probe in parallel.

There is only one known protocol for which any of this
works, as pointed out earlier - TCP. 

Using non IP reliable full-duplex connection transports requires
redoing the rest of the URL anyway (to change the interpretation of the
host address and port, which is IPv4-specific), so using a new protocol
ID (http-tp4:) is necessary anyway.

Supporting HTTP over non full-duplex, connection-oriented protocols
requires other modificiations - i.e., serial numbers to associate
responses with requests, at least.

What is the advantage to a transparent selection of transport
protocol, given these constraints??

Joe Touch - touch@isi.edu		    http://www.isi.edu/~touch/
ISI / Project Leader, ATOMIC-2, LSAM       http://www.isi.edu/atomic2/
USC / Research Assistant Prof.                http://www.isi.edu/lsam/
Received on Wednesday, 19 February 1997 09:49:46 UTC

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