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RUCUS Exploratory Working Group                                  D. Wing
Internet-Draft                                                     Cisco
Intended status:  Experimental                              S. Niccolini
Expires:  August 16, 2008                                 M. Stiemerling
                                                                     NEC
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                       February 13, 2008


                           Spam Score for SIP
                    draft-wing-sipping-spam-score-01

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This document defines a mechanism for SIP proxies to communicate a
   spam score to downstream SIP proxies and to SIP user agents.  This
   information can then be used as input to other decision making
   engines, for example, to provide alternate call routing or call



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   handling.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Operation of Spam-Scoring Proxy . . . . . . . . . . . . . . . . 3
   4.  Operation of Proxy or User Agent  . . . . . . . . . . . . . . . 4
   5.  Grammar . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     10.1.  Normative References . . . . . . . . . . . . . . . . . . . 6
     10.2.  Informational References . . . . . . . . . . . . . . . . . 7
   Appendix A.  Changes  . . . . . . . . . . . . . . . . . . . . . . . 7
     A.1.   Changes from -00 to -01  . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9






























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1.  Introduction

   It is desirable for SIP proxies to insert a spam score so that
   downstream SIP proxies and downstream SIP user agents can use a high
   score to decide that special handling is required.  For example, a
   score above 20 might cause one of the spam avoidance techniques
   described in [RFC5039] to be triggered for this call.

   This specification allows each SIP proxy to contribute spam scoring
   information that can be useful to downstream SIP proxies and the SIP
   user agent (UA).  The downstream SIP proxies or SIP UA might ignore
   that information (e.g., it doesn't trust the SIP proxy that generated
   the spam score) or might use it.

   Note that this document does not make the attempt to define how the
   spam score was derived nor to distribute information that could be
   used to verify the spam score generation.  Furthermore, this document
   does not attempt to cryptographically bind the identity of the entity
   generating the score to the value itself.  Hence, its usage is likely
   to be useful only between neighboring administrative domains
   communicating such a score.


2.  Terminology

   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 [RFC2119].


3.  Operation of Spam-Scoring Proxy

   A SIP proxy evaluates an incoming SIP request and generates a spam
   score using a local mechanism.  This score is between 0 (indicating
   the message is not spam) and 100 (indicating the message is spam).
   Values between 0 and 100 indicate the 'likelihood' that the SIP
   request is spam, with higher values indicating a higher likelihood
   the message is spam.

   This spam score is inserted into the new "Spam-Score" header.  This
   header field contains a summary spam score and optionally contains
   detail information.  The detail information is implementation
   dependent.  The detail information is valuable for debugging and to
   provide the SIP user agent or SIP proxy with additional information
   regarding how the spam-scoring SIP proxy's local mechanism arrived at
   the summary spam score.





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4.  Operation of Proxy or User Agent

   A downstream proxy or the SIP user agent MAY use the spam score or
   spam-detail information to change call routing or call handling.  It
   is envisioned that some form of policies indicate the trusted proxies
   in order to decide which spam scores to consider for special call
   treatment.

      In some jurisdictions, the end user needs to authorize call
      handling, including rejection of a call based on a spam score.
      Mechanisms to allow users to influence such policies are, however,
      out of scope of this document.

   The behavior of the SIP proxy or user agent when the spam score is
   above a certain value is a local policy matter.  Examples of behavior
   include:

   o  a SIP request with a high spam score might cause a proxy or user
      agent to redirect the SIP request to company's main telephone
      extension or to the user's voicemail

   o  a user agent might alert the user by flashing the phone (without
      audible ringing)

   o  a user agent might allow calls with a spam score below a certain
      value during daylight hours, but deny such calls at night.

   o  a proxy might challenge the caller to complete a Turing test.























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5.  Grammar

   ABNF using the ABNF syntax of [RFC3261]:

     extension-header   = spam-score [ SP ";" spam-detail ]

     spam-score         = score SP "by" SP hostname
     score              = 1*3DIGIT [ "." 0*3DIGIT ]

     spam-detail        = "detail" EQUAL detail
     detail             = QUOTE mech SEMI rule-score
                          *(COMMA rule-score) QUOTE
                          ; mathematical average of the rule-scores
                          ; MUST be same as spam-score

     rule-score         = rule [ "=" score ]
     mech               = token
     rule               = token

                              Figure 1: ABNF


6.  Examples

   The following example shows a SIP score generated and inserted by two
   SIP proxies, sip.example.com and sip.example.net.  In this example,
   sip.example.com is owned by a spammer who is trying to fool
   downstream systems with their low spam score (0).  However, the
   example.net proxies and user agents only pay attention to spam scores
   from Spam-Score headers generated by example.net proxies, so
   example.com's attempts to fool the downstream proxies (with its low
   spam score) are in vain.



















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     INVITE sip:bob@example.net SIP/2.0
     Via: SIP/2.0/UDP sip.example.net;branch=z9hG4bKnashds8
       ;received=192.0.2.1
     Spam-Score: 75 by sip.example.net
       ;detail="SIPfilter-1.0;call_volume=75"
     Via: SIP/2.0/UDP sip.example.com;branch=z9hG4bKfjzc
       ;received=192.0.2.127
     Max-Forwards: 70
     To: Bob <sip:bob@example.net>
     From: Alice <sip:alice@example.com>;tag=1928301774
     Call-ID: a84b4c76e66710@pc33.example.com
     CSeq: 314159 INVITE
     Contact: <sip:alice@pc33.example.com>
     Content-Type: application/sdp
     Content-Length: 142

     [... SDP elided from this example...]

                    Figure 2: Example with spam scores


7.  Security Considerations

   SIP proxies and SIP user agents need to ignore spam scores generated
   by proxies that aren't trusted.

   [[This section will be completed in a later version of this
   document.]]


8.  Acknowledgements

   Thanks to Joachim Charzinski, Daniel Quinlan, and S. Moonesamy for
   their suggestions to improve this document.


9.  IANA Considerations

   [[This section will be completed in a later version of this
   document.]]


10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.



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   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

10.2.  Informational References

   [RFC5039]  Rosenberg, J. and C. Jennings, "The Session Initiation
              Protocol (SIP) and Spam", RFC 5039, January 2008.


Appendix A.  Changes

   Note to RFC Editor:  please remove this section prior to publication.

A.1.  Changes from -00 to -01

   o  Changed scoring from positive/negative to 0-100 range.

   o  Moved score from a "Via:" extension to a new header "Spam-Score:".

   o  Changed from Standards Track to Experimental.


Authors' Addresses

   Dan Wing
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email:  dwing@cisco.com


   Saverio Niccolini
   Network Laboratories, NEC Europe Ltd.
   Kurfuersten-Anlage 36
   Heidelberg  69115
   Germany

   Phone:  +49 (0) 6221 4342 118
   Email:  saverio.niccolini@netlab.nec.de
   URI:    http://www.netlab.nec.de







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   Martin Stiemerling
   Network Laboratories, NEC Europe Ltd.
   Kurfuersten-Anlage 36
   Heidelberg  69115
   Germany

   Phone:  +49 (0) 6221 4342 113
   Email:  stiemerling@netlab.nec.de
   URI:    http://www.netlab.nec.de


   Hannes Tschofenig
   Nokia Siemens Networks
   Linnoitustie 6
   Espoo  02600
   Finland

   Phone:  +358 (50) 4871445
   Email:  Hannes.Tschofenig@nsn.com
   URI:    http://www.tschofenig.com































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Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

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Acknowledgments

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).  This document was produced
   using xml2rfc v1.33pre66 (of http://xml.resource.org/) from a source
   in RFC-2629 XML format.



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