DISPATCH H. Schulzrinne
Internet-Draft FCC
Intended status: Standards Track September 30, 2016
Expires: April 3, 2017

A SIP Response Code for Unwanted Calls


This document defines the 666 (Unwanted) SIP response code, allowing called parties to indicate that the call was unwanted. The terminating SIP entity may use this information to adjust future call handling behavior for this called party or more broadly.

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Table of Contents

1. Introduction

In many countries, an increasing number of calls are unwanted [RFC5039], as they might be fraudulent, illegal telemarketing or the receiving party does not want to be disturbed by, say, surveys or solicitation by charities. Carriers and other service providers may want to help their subscribers avoid receiving such calls, using a variety of global or user-specific filtering algorithms. One input into such algorithms is user feedback. User feedback may be offered through smartphone apps, APIs or within the context of a SIP-initiated call. This document addresses only the last mode, where the called party either rejects the SIP INVITE request as unwanted or terminates the call with a BYE request after answering the call. To allow the called party to express that the call was unwanted, this document defines the 666 (Unwanted) response code.

2. Normative Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119].

3. Motivation

None of the existing 4xx, 5xx or 6xx response codes allow the called party to convey that they not only reject this call, e.g., using 480 (Temporarily Unavailable), 486 (Busy Here), 600 (Busy Everywhere), 603 (Decline) or 606 (Not Acceptable), but that the caller is unwanted. The particular response code number was chosen to reflect the distaste felt by many upon receiving such calls.

4. Behavior of SIP Entities

The SIP entities receiving this response code are not obligated to take any particular action. The service provider delivering calls to the user issuing the response MAY, for example, add the calling party to a personal blacklist, or MAY use the information as input when computing the likelihood that the calling party is placing unwanted calls ("crowd sourcing").

The response code MAY also be used in Reason header fields [RFC3326], typically when the UAS issues a BYE request terminating an incoming call.

5. IANA Considerations

This document register a new SIP response code. This response code is defined by the following information, which is to be added to the method and response-code sub-registry under http://www.iana.org/assignments/sip-parameters.

Response Code Number
Default Reason Phrase
[this RFC]

6. Security Considerations

If the calling party number is spoofed, users may report the number as placing unwanted calls, possibly leading to the blocking of calls from the legitimate user of the number in addition to the unwanted caller. Thus, it is RECOMMENDED that the response code is used for creating call filters only if the calling party number has been authenticated using [I-D.ietf-stir-rfc4474bis].

7. Acknowledgements


8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, DOI 10.17487/RFC3261, June 2002.
[RFC3326] Schulzrinne, H., Oran, D. and G. Camarillo, "The Reason Header Field for the Session Initiation Protocol (SIP)", RFC 3326, DOI 10.17487/RFC3326, December 2002.

8.2. Informative References

[I-D.ietf-stir-rfc4474bis] Peterson, J., Jennings, C., Rescorla, E. and C. Wendt, "Authenticated Identity Management in the Session Initiation Protocol (SIP)", Internet-Draft draft-ietf-stir-rfc4474bis-13, September 2016.
[RFC5039] Rosenberg, J. and C. Jennings, "The Session Initiation Protocol (SIP) and Spam", RFC 5039, DOI 10.17487/RFC5039, January 2008.

Author's Address

Henning Schulzrinne FCC 450 12th Street SW Washington, DC 20554 US EMail: henning.schulzrinne@fcc.gov