A Session Initiation Protocol (SIP) Response Code for Rejected Calls

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SIPCORE                                                        E. Burger
Internet-Draft                                     Georgetown University
Intended status: Standards Track                         August 21, 2018
Expires: February 22, 2019

  A Session Initiation Protocol (SIP) Response Code for Rejected Calls


   This document defines the 608 (Rejected) SIP response code.  This
   response code enables calling parties to learn their call was
   rejected by an intermediary and will not be answered.  As a 6xx code,
   the caller will be aware that future attempts to contact the same UAS
   will be likely to fail.  The present use case driving the need for
   the 608 response code is when the intermediary is an analytics
   engine.  In this case, the rejection is by a machine or other
   process.  This contrasts with the 607 (Unwanted) SIP response code,
   which a human at the target UAS indicated the call was not wanted.
   In some jurisdictions this distinction is important and may have
   additional requirements beyond the 607 response code.  Specifically,
   this document defines the use of the Call-Info header in 608
   responses to enable rejected callers to contact entities that blocked
   their calls in error.

Status of This Memo

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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

Burger                  Expires February 22, 2019               [Page 1]
Internet-Draft               Status Rejected                 August 2018

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1.  Introduction

   The IETF has been addressing numerous issues surrounding how to
   handle unwanted and, depending on the jurisdiction, illegal calls
   [RFC5039].  Technologies such as STIR [RFC7340] and SHAKEN [SHAKEN]
   address cryptographic signing and attestation, respectively, of
   signaling to ensure the integrity and authenticity of the asserted

   This document describes a new SIP response code, 608, which allows
   calling parties to learn an intermediary rejected their call.  As
   described below, we need a distinct indicator to differentiate
   between a user rejection and an intermediary's rejection of a call.
   In some jurisdictions, calls, even if unwanted by the user, may not
   be blocked unless there is an explicit user request.  Moreover, users
   may misidentify the nature of a caller.  For example, a legitimate
   caller may call a user who finds the call to be unwanted.  However,
   instead of marking the call as unwanted, the user may mark the call
   as illegal.  With that information, an analytics engine may determine
   that all calls from that source should be blocked.  However, in some
   jurisdictions blocking calls from that source for other users may not
   be legal.  Likewise, one can envision jurisdictions that allow an
   operator to block such calls, but only if there is a remediation
   mechanism in place to address false positives.

   Some call blocking services may return responses such as 604 (Does
   Not Exist Anywhere).  This might be a strategy to attempt to get a
   destination's address removed from a calling database.  However,
   other network elements might interpret this to mean the user truly
   does not exist and result in the user not being able to receive calls
   from anyone, even if wanted.  As well, in many jurisdictions,
   providing false signaling is illegal.

   The 608 response code addresses this need of remediating falsely
   blocked calls.  Specifically, this code informs the UAC an
   intermediary blocked the call and, to satisfy some jurisdictional
   requirements for providing a redress mechanism, how to contact the
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