Subject: RE: On attribute-based queries

From: Stuart Cheshire <[email-masked]>
Date: Wed, 7 Aug 2002 16:05:47 -0700

This is a good real-world example:

>A typical rig for a show in a 150 seat theatre will probably
>involve about 80 lamps, each with colour scrollers.  To avoid
>ladder or tower climbing, remote positioners would be nice (we
>can't afford to hire them yet....). This comes to 240 devices
>which have to be installed, configured and tested in 6 hours.

The crux of the debate between SLP and DNS-SD is the assertion that you 
need a complicated attribute-query-based service discovery protocol, 
because a simple protocol couldn't work in a network this large.

So, the question is this:

  Could a simple protocol work on a network with 240 devices, or more?

Perhaps we can find existing operational experience by looking at what 
people did using the old AppleTalk Name Binding Protocol, a very 
simple-minded protocol.

Over to you, Tony:

>I have done projects with up to 10000 lighting channels, however
>this doesn't mean you need 10000 IP addresses. Lighting channels
>are normally bundled in dimmer packs and moving lights etc. So the
>real demand in terms of addressing capabilities is probably closer
>to less than 2000 in my example.
>
>Using AppleTalk over Ethernet we had systems like this set up in
>a very short time with virtually no network configuration time.

If something as exceedingly simple-minded and inefficient as AppleTalk 
NBP worked for Tony de Rijk in this environment, we need to look 
elsewhere for evidence that a complicated attribute-query-based service 
discovery protocol is worth the cost.

Stuart Cheshire <[email-masked]>
 * Wizard Without Portfolio, Apple Computer
 * Chairman, IETF ZEROCONF
 * www.stuartcheshire.org

---

From: Erik Guttman <[email-masked]>
Date: Thu, 8 Aug 2002 13:11:32 +0200 (CEST)

> need a complicated attribute-query-based service discovery protocol, 

I disagree that the SLP protocol is complicated.  We're back to esthetics.

> because a simple protocol couldn't work in a network this large.

There is more to it than this.  If you do not have attribute based 
queries, each service has to handle server feature discovery.  So,
by making the service discovery simpler you make applications more
complex.

Erik