Subject: Re: [SIMPLE] Mechanism for sending service-state notifications to a handset

From: Jonathan Rosenberg <[email-masked]>
Date: Mon, 07 Mar 2005 01:27:26 -0500

This is mostly off topic for SIMPLE, but replies inline.

[email-masked] wrote:

> 
> Hi,
> 
> In TDM-networks, the service offering includes "supplementary services", 
> such as call forwarding (on busy, no reply, unconditional, ...), 
> CLIP/CLIR, call barring, etc.  When call forwarding (CF) is activated, a 
> user typically is notified of this situation when he lifts the hook, 
> either by a stutter tone or by an announcement that informs him/her of 
> the condition.
> 
> As one possible use of SIP telephony is to replace a TDM-network, this 
> CF notification should also be implemented in a SIP network.  It will be 
> impossible to implement this in the same way as in a TDM network, since 
> in a TDM network, the switch is aware of the activation of the call 
> forwarding service and the switch detects when a phone is off-hook, and 
> thus can play the stutter dial-tone or the notification.  In a SIP 
> network, the softswitch is aware of the activation of the call 
> forwarding, but the off-hook condition is typically not detected by the 
> softswitch, but by the handset.  But the handset may not be aware of the 
> activation of the call forwarding condition.
> Two solutions seem evident:
> 
>    1. the handset notifies the softswitch of the off-hook condition, so
>       the softswitch can play the notification or the stutter dial-tone
>    2. the softswitch notifies the handset of the status of services, so
>       the handset can show indicators or play notifications or tones

This is a softswitch centric view of the problem. In SIP, there is no 
such thing as off-hook conditions. In a softphone, there is no hook.

The problem you are asking is: how can a SIP user agent know that call 
forwarding has been activated for it?

The answer is that it is dependent on how call forwarding is provisioned 
in the network. I happen to think that we should (in sipping, not here), 
define an xcap usage for forwarding configuration, and then a user agent 
can read the forwarding information that is in place, or set it.

Based on this, a SIP UA that is in a dumb phone (or a phone adaptor), 
could, on "off hook", go and fetch the xml document, and if forwarding 
is indicated as activated, play the tone. A smart UA, such as a 
softphone, could render this appropriately in a dialog window. By using 
explicit signaling, different user interfaces and device types are 
supported with the same protocols.

-Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
Director, Service Provider VoIP Architecture   Parsippany, NJ 07054-2711
Cisco Systems
[email-masked]                              FAX:   (973) 952-5050
http://www.jdrosen.net                         PHONE: (973) 952-5000
http://www.cisco.com

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