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

[Benjamin on Asterisk Mailing Lists]

I spent some time with Stuart Cheshire, the driving force behind
Apple's Zeroconf implementation, which they call Rendezvous. We agreed
to work together to bring Rendezvous support to Asterisk. What this
means is, I will be doing the work and Apple will provide assistance
in respect of Rendezvous.

For those who are unfamiliar with Rendezvous/Zeroconf, it is a
technology to use DNS SRV records to dynamically advertise service
availability and service parameters to clients on the network.

http://www.zeroconf.org

Anyway, the idea is to let Asterisk advertise services so that IP
phones can discover those services and configure themselves
automatically. The libraries are built in to Darwin and Apple has
released the code as open source with Linux compatibility. A Windoze
version is available as a technology preview.

The API is very straigtforward. The only functions required from the
viewpoint of a server are DNSServiceRegister, DNSServiceUpdateRecord
and DNSServiceDeallocate (though the mDNSresponder will automatically
deregister services when the process that registered them exits).

So building a module for Asterisk to advertise services by calling
those functions shouldn't be all to difficult. The part that will need
a little more effort in form of careful thought is how to tell
Asterisk which services it should advertise and what service
parameters should be advertised. It is this part that I would like to
ask interested parties for input/suggestions.

Let me first give you a better view of the DNSServiceRegister function ...

DNSServiceErrorType DNSServiceRegister(
DNSServiceRef *sdRef,
DNSServiceFlags flags,
uint32_t interfaceIndex,
const char *name,
const char *regtype,
const char *domain,
const char *host,
uint16_t port,
uint16_t txtLen,
const void *txtRecord,
DNSServiceRegisterReply callBack,
void *context);

An example of a SIP service being advertised would be:

name = "Flintstones Inc. Internal Telephone Service"
regtype = "SIP"
domain = "local"
host = "pbx"
port = 5060

and txtRecord which would show up as a DNS TXT record, could contain
various service parameters like authentication method, registrar
server, outbound proxy, dtmfmode, contact, voicemail access number etc
etc. For IAX, switchboard extension and incoming context could also be
advertised here.

For starters I envisage the following two scenarios:

1) New IP telephone set deployment

The phone would be put on a user's desk, connected to the LAN and
power, switched on and the menu would display a list of advertised
services. The "telephone guy" would select the appropriate service and
all service parameters would be set accordingly, leaving only the user
ID and password to be supplied. This could be further automated by an
IVR that an employee calls to be provisioned.

2) Walk-in guest user, ie Hotel

The WiFi phone would be switched on at the Hotel's premises and the
Hotel's welcome service would show up on the display. The user would
select the service and thereby be enabled to call an IVR that walks
him through the necessary steps to receive service, ie establishing
prepaid credit or key in a code received at check-in which triggers
automatic provisioning. A similar situation could be imagined for a
travelling employee visiting a remote office.

I am sure there are more scenarios. As with so many things the
potential will probably only become visible once using it.

Anyway, with those starter scenarios in mind, I was trying to come up
with an idea how to tell Asterisk what to advertise and what
parameters to advertise. I am split between a decidated zeroconf.conf
configuration file for the details or adding a few things to sip.conf,
iax.conf etc. The answer probably lies somewhere in between.

For example, if we look at how voicemail is configured, this could
serve as a model:

voicemail.conf ...

1000 => ...

sip.conf ...

[user]
...
mailbox=1000

If we were to use this as a blueprint, then we might do something like this:

For scenario #1

zeroconf.conf ...

[internal]
enable=yes
bindaddr=192.168.77.99 ; only advertise on this interface
servicename="Flintstones Inc. Internal Telephone Service
(authentication required)"
username=no ; do not advertise usernames -- this would be the default
auth=yes ; advertise authentication method
vmaccess=8500 ; advertise voicemail access number

sip.conf ...

[2001]
...
zeroconf=internal ; referring to the entry [internal] in zeroconf.conf

[2002]
...
zeroconf=internal ; referring to the entry [internal] in zeroconf.conf

A potential problem I see here would be different users having
different parameters amongst those to be advertised. Not sure yet how
to resolve this.

For scenario #2

zeroconf.conf ...

[walk-in]
enable=yes
servicename="Flintstones Hotel Walk-in Telephone Service"
username=yes ; advertise username
auth=yes ; advertise authentication method
dtmfmode=yes ; advertise dtmfmode
contact=7000 ; advertise switchboard/IVR contact number

sip.conf ...

[guest]
...
zeroconf=walk-in ; referring to the entry [walk-in] in zeroconf.conf


Any comments as to the how and what are appreciated.

Anybody who has issues with zeroconf as such please start a new thread
and discuss there, don't hijack this one as this one is solely aimed
at discussing the how and what.

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

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