[Asterisk-Dev] Rendezvous (aka Zeroconf) for Asterisk

[Benjamin on Asterisk Mailing Lists]

On Fri, 12 Nov 2004 08:30:03 +0100, Holger Schurig
<hs4233 at mail.mn-solutions.de> wrote:
> Why not use something that is already used by other softwares, e.g.
> the Service Location Protocol?

If you look at SCO's (ex? main-sponsor, SIGH!!!) project website you
will find that it looks somewhat abandoned (for example the FAQ page
is in a perpetual state of coming soon). Compare this with Apple's
support pages for Rendezvous/Zeroconf and you will understand right
away why Zeroconf is receiving so much attention and support, while
SLP fares only very modestly.

>From a technical viewpoint, Zeroconf is favourable because it does not
need any additional infrastructure to work. Take two zeroconf devices
out of the box, connect them, power them up and they will talk to each
other: The name says it all: Zero Configuration! SLP relies on other
infrastructure such as LDAP and/or DHCP servers to be there or it will
fail.

But don't take my word for it. There has been quite some debate on
this in other forums and a good summary can be found at Elanthis'
Corner

http://www.awemud.net/blogs/elanthis/index.php/archives/2004/03/25/127

"So it comes down to Zeroconf vs SLP. In my mind, Zeroconf is the
clear winner so far as the protocol goes. Why? First, it leverages
existing code and infrastructure - DNS. SLP requires all new code and
expertise/training on the part of programmers and admins. Second,
Zeroconf is very widely used in consumer and network devices already
thanks to Apple's Rendezvous marketing. Hard to find a new network
printer without Zeroconf support, for example. Finally, it's capable
of doing everything SLP can and then some.

Zeroconf works fine both for home users (zero configuration, after
all), ad-hoc networks (did we mention zero configuration?), and
corporate networks (the service discovery protocol, dns-sd, allows you
to do configuration and management if you really want/need to). In the
case of the former two situation, applications and systems can easily
start using Zeroconf with no need for new system components are
architecture, so long as link-local connections are on. (Which SLP
would need in order to work in a similar fashion anyhow.) In a
corporate network, DNS-SD could be configured to not publish services
over link-local addressing (which would probably be disabled) and
service browsers can look at corporate DNS servers. You could even
still allow service publishing from client machines using one of the
dns-update protocol extensions, with all sorts of policy control on
the server as well. Just like SLP. Really, in terms of protocol,
Zeroconf is pretty clearly a solid winner."

> Also, because it doesn't need to modify some entries in some DNS server
> it should be easier to deploy. Not every DNS server allows modification
> of service level entries.

That's a clear misinterpretation of what Zeroconf does on your part.
Zeroconf does not need any DNS server nor LDAP server nor DHCP server.
It uses the DNS protocol, but it doesn't mean that it will poke around
in your DNS server's database. By default it does not.

There are two components, mDNS (the multicast DNS daemon) which is
used to advertise services and DNS-SD the service discovery daemon.
These are part of Zeroconf and you don't need anything else.

In understand that Apple is working on extensions to let Zeroconf talk
to DNS servers, including dynamic DNS so you can advertise services
globally. But this is an option, not a requirement.

But of course, you are free to write an app_slp module for Asterisk. I
will continue to work towards app_zeroconf. Users can then make their
own choice which one they want to use.

rgds
benjk
-- 
Sunrise Telephone Systems, 9F Shibuya Daikyo Bldg., 1-13-5 Shibuya,
Tokyo, Japan.

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