Subject: SIP registration

From: [email-masked] (Pradeep Malhotra)
Date: Tue, 15 Jun 1999 10:06:38 -0700

Hi,
	I am new to SIP specifications. I have a basic doubt about the 
	registration process of the users with SIP servers. Let's say there
	is a domain company.com which has a number of hosts. A user is
	logged on to four different hosts simultaneously. There is a user agent
	server on each host and there is one SIP proxy server in the domain. 
	
	Does the user have to register with each user agent server for SIP
	services or to the SIP proxy server? Is there a possibility that the
	user does not register at all and when an inoming invitaion arrives at 
	the SIP proxy, it could find the user's current hosts using location
	services?
	
	Your help is appreciated..
	
regards,
pradeep

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From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 15 Jun 1999 14:45:25 -0400

>         the SIP proxy, it could find the user's current hosts using location

There are many valid possibilities according to the protocol spec. Which
one is actually done depends on the configuration of the software and
the needs of the application:

1. each of the four user agents registers the same name
([email-masked]). When a call for [email-masked] arrives at the
proxy, it can be forwarded to any one (or all) of these hosts, according
to its configuration and policy.

2. one of the hosts can perform the registration for the others. The
software probably couldn't do this automatically, but a user could sit
at one host, and register all four hosts to the same name in a single
registration message.

3. Registration is optional. The proxy server could use a location
service to locate which hosts the user is logged in on, if such a
service were available, rather than depending on registrations.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       Lucent Technologies
Member of Technical Staff                   101 Crawfords Corner Rd.
High Speed Networks Research                Holmdel, NJ 07733
FAX:   (732) 834-5379                       Rm. 4C-526
EMAIL: [email-masked]
URL: http://www.cs.columbia.edu/~jdrosen

---

From: Dean Willis <[email-masked]>
Date: Tue, 15 Jun 1999 22:40:14 -0500

> service were available, rather than depending on registrations.

A fourth option would be for each host to register a unique identity, like
"host1.company.com" and so on. The user profile for "user" in proxy
"sip.company.com" might manually provision "host1.company.com" and so on as
potential contacts, and the behavior of "sip.company.com" might be to fork
invites to "[email-masked]" to the set of provisioned contacts which are
also registered. This behavior is especially interesting if one wishes to
adopt the PBX modality of assigning a numeric extension to each handset and
only listing a few users by name in the dirctory. This allows the handset to
function as a normal phone if a random user tries to place or receive calls
from it.

--
Dean Willis