Re: [sipcore] Motivation for submission of RFC

[Ranjit Avasarala <[e-mail]>]

Hi Shrawan

So essentially you are trying to propose a new SIP 4xx response code with
optional warning code to indicate to UA the reason why the network did not
accept the call transfer request.  Though it may be useful, it may not be
like an essential feature that many network vendors and service providers
may be willing to support.

Still we can try and see how the reaction is from experts

Regards
Ranjit


On Thu, Mar 11, 2021 at 12:16 PM Shrawan Khatri <[e-mail]>
wrote:

> Hello SIPCORE Chair and SIPCORE team,
>
> Please find the motivation behind this RFC draft.
>
>
>
> Regards,
>
> Shrawan Khatri and team
>
>
>
> *The purpose of the draft*
>
> Signaling plane and Media plane of an IMS calls can be transferred between
> devices using IMS Signaling. There are various reasons why an on-going call
> cannot be transferred between the devices. Some of these reasons are policy
> driven, for instance: the call to be transferred is in the circuit switched
> (CS) domain and the operator's policy does not allow transfer of a CS call,
> the call is an emergency call and the operator's policy does not allow
> transfer of an emergency call, the call is a mobile-terminated call and the
> operator's policy does not allow transfer of a mobile-terminated call, or
> the call is a video call and the operator's policy does not allow transfer
> of a video call. The user agent (UA) initiating the call transfer procedure
> will be notified of any failure through a SIP response code. However the
> existing SIP response codes are not suitable to adequately convey the
> information regarding why the call transfer request is not accepted by the
> network. This is because handling of these existing response codes has
> already been implemented by various devices, with an associated device
> behavior defined for a specific purpose not related to call transfer. For
> instance, upon receiving some of these response codes, such as 403
> (Forbidden), the device may initiate IMS re-registration procedure, which
> is not needed in case of Call Pull/Call Push failure and will result in
> unnecessary SIP signaling.
>
>
>
> A method is defined in this draft such that a call transfer failure SIP
> response code is defined along with an optional warning code in a Warning
> header field to convey the exact reason why the call could not be
> transferred, so that the UA can determine the subsequent steps (e.g. call
> termination) and optionally provide an indication of the reason for the
> failure to the user.
>
>
>
> *Intended target audience*
>
> The following is the intended audience of this RFC:
>
> •             IMS Core Network Planners that support IMS call transfer
> across multiple devices.
>
> •             IMS System Designer and Developers of IMS Core Network and
> User Agent that support call transfer using IMS Signaling.
>
>
>
> *Benefit*
>
> •             In the absence of this new mechanism,
>
> o             The IMS Core network has to rely on existing SIP response
> codes, for which a specific device behavior has already been defined. For
> instance, upon receiving some of these response codes, such as 403
> (Forbidden), the device may initiate IMS re-registration procedure, which
> is not needed in case of call transfer failure and will result in
> unnecessary SIP signaling.
>
> o             The existing SIP response codes do not accurately convey the
> reason for the call transfer failure.
>
>
>
> •             With the new mechanism
>
> o             A specific behavior can be defined for the new SIP response
> code.
>
> o             Unnecessary SIP signaling may be avoided.
>
> o             A User Agent may develop intelligent algorithms for
> subsequent call transfer procedure based on the warning code received in
> the Warning header field along with the new SIP response code.
>
>
>
> Name:                  draft-khatri-sipcore-call-transfer-fail-response
>
> Revision:              00
>
> Title:                      A SIP Response Code (497) for Call Transfer
> Failure
>
> Document date:               2021-03-11
>
> Group:                  Individual Submission
>
> Pages:                   10
>
> URL:
> https://www.ietf.org/archive/id/draft-khatri-sipcore-call-transfer-fail-response-00.txt
>
> Status:
> https://datatracker.ietf.org/doc/draft-khatri-sipcore-call-transfer-fail-response/
>
> Htmlized:
> https://datatracker.ietf.org/doc/html/draft-khatri-sipcore-call-transfer-fail-response
>
> Htmlized:
> https://tools.ietf.org/html/draft-khatri-sipcore-call-transfer-fail-response-00
>
>
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