Subject: [SPIRITS] Re: SPIRITS digest, Vol 1 #64 - 1 msg

From: [email-masked]
Date: Fri, 21 Mar 2003 11:32:33 +0530

hi folks,

If the User needs only the Redirection Service and wants to know about the
Incoming Call, then in the "Subscribe" Message itself  can specify the details
of the
redirection. Then if a call is ended to the user, then he will just be informed
through the "Notify" message and the Call is redirected. But in this case he has
no
choice, other than the call being redirected. In this case the Service is much
much lighter too.
Do I make any sense?

Talking about the INVITE and NOTIFY, definetly both the messages can be used
to invoke a service at the Application Server.

thanks
UCB

[email-masked] on 03/20/2003 10:31:08 PM

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Subject:  SPIRITS digest, Vol 1 #64 - 1 msg

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Today's Topics:

   1. Redirection in SPIRITS (Vijay K. Gurbani)

Message: 1
Date: Wed, 19 Mar 2003 16:33:45 -0600
From: "Vijay K. Gurbani" <[email-masked]>
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Folks:

One issue that has come up in conjunction to the services
enabled by SPIRITS is how to best do redirection.  For
instance, an application server may subscribe to the equivalent
of a Terminating Attempt Authorized trigger (or Terminating
Busy trigger) to perform redirection services.  How do we
realize such services in SPIRITS?

So far, using ICW as a canonical example, the PSTN sends an
INVITE and expect a 3xx response redirecting it to alternative
destinations.  However, given the advent of events in the SIP
WG, there is a better way to do these types of services which
does not require the heavy-weight processing of the INVITE
transaction.  And that is the use of "message/sipfrag" MIME
type (http://www.ietf.org/rfc/rfc3420.txt).

Using this, the 200 OK (NOTIFY) from the application server (which
is a SPIRITS server as well), instead of containing an empty
body, will instead contain a body of MIME type "message/sipfrag".
The body will include fragments of a 3xx final response,
including the Contacts to redirect the call to.

Here is a sample call flow:

PSTN               App Server
   |<-------------------+ SUBS (body: application/spirits-event)
   +------------------->| 200 OK
  ...                  ...
   +------------------->| NOT (body: application/spirits-event)
   |<-------------------+ 200 OK (body: message/sipfrag)

Of course, this does not deprecate or obsolete the use of an
INVITE request; but rather it is yet another (light-weight) way
to do redirection services in SIP.

Comments/questions/opinions welcome.

Regards,

- vijay
--
Vijay K. Gurbani  vkg@{lucent.com,research.bell-labs.com,acm.org}
Wireless Networks Group/Internet Software and Services
Lucent Technologies/Bell Labs Innovations, 2000 Lucent Lane, Rm 6G-440
Naperville, Illinois 60566     Voice: +1 630 224 0216

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---

From: "Vijay K. Gurbani" <[email-masked]>
Date: Mon, 24 Mar 2003 10:02:36 -0600

[email-masked] wrote:
> Incoming Call, then in the "Subscribe" Message itself  can specify the 
> details of the redirection. 

One thing we do NOT want to do in SPIRITS is to outline specific
services.  We do want to *enable* services.  To that extent, having
the SUBSCRIBE specify details of the redirection would be attempting
to specify the service.  On the other hand, if SUBSCRIBE conatined
the normal payload -- events to be monitored -- then the framework
remains general enough and the specific redirection service is
realized as outlined in my original email.

> to invoke a service at the Application Server.

Exactly; using the mechanism I proposed does not invalidate the use
of INVITE.

Regards,

- vijay