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Network Working Group                                            D. Wing
Internet-Draft                                             Cisco Systems
Intended status:  Standards Track                           S. Niccolini
Expires:  February 19, 2008                                          NEC
                                                           H. Tschofenig
                                                  Nokia Siemens Networks
                                                          M. Stiemerling
                                                                     NEC
                                                         August 18, 2007


                           Spam Score for SIP
                  draft-wing-sipping-spam-score-00.txt

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on February 19, 2008.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document defines a mechanism for SIP proxies to communicate a
   spam score to downstream SIP proxies and SIP user agents so they can
   provide alternate call routing or call handling.



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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].


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Operation of Spam-Scoring Proxy . . . . . . . . . . . . . . . . 3
   3.  Operation of Proxy or User Agent  . . . . . . . . . . . . . . . 3
   4.  ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     9.2.  Informational References  . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8





























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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 [I-D.ietf-sipping-spam], 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
   UA.  The downstream SIP proxies might ignore that information (e.g.,
   they don't trust it) or might use it (e.g., they trust it because it
   was generated by a federation).

   From a deployment point of view it is expected that the score will
   most likely be benefical (and trustworthy) when inserted by a SIP
   proxy on the recipients side for evaluation by a SIP UA that has a
   direct relationship with this SIP proxy.


2.  Operation of Spam-Scoring Proxy

   A SIP proxy generates a spam score using a local mechanism.  Negative
   scores indicate the SIP request is not considered spam, and positive
   scores indicate the SIP request is considered spam.  The higher the
   value, the more likely a message is spam or is not spam.

   This spam score is inserted into the "Via:" header, which is already
   generated by the proxy.

      The Via header was chosen because it the Via is already correlated
      with the proxy that generated the Via header.


3.  Operation of Proxy or User Agent

   A downstream proxy MAY use the spam score or spam-detail information
   to change call routing or call handling.  It is RECOMMENDED that only
   scores generated by trusted proxies be used.  The behavior of the SIP
   proxy or user agent when the spam score is above a certain value is a
   local 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)



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   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.

   These aspects are discussed in
   [I-D.tschofenig-sipping-framework-spit-reduction].


4.  ABNF

   ABNF using the ABNF syntax of [RFC3261]:

     via-extension      = spam-score / spam-detail

     spam-score         = "spam" EQUAL score
     score              = *"-" 1*4DIGIT [ "." 0*3DIGIT ]

     spam-detail        = "spam-detail" EQUAL detail
     detail             = QUOTE mech SEMI rule-score
                          *(COMMA rule-score) QUOTE
     rule-score         = rule [ "=" score ]
     mech               = token
     rule               = token

                              Figure 1: ABNF

























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5.  Examples

   The following example shows a SIP score generated by biloxi.com and
   atlanta.com.  In this example, atlanta.com is owned by a spammer who
   is trying to fool downstream systems with their low spam score (0.0).
   However, the biloxi.com proxies and user agents only pay attention to
   spam scores from Via:  headers generated by biloxi.com proxies, so
   atlanta.com's attempts are in vain.

     INVITE sip:bob@biloxi.com SIP/2.0
     Via: SIP/2.0/UDP biloxi.com;branch=z9hG4bKnashds8
       ;received=192.0.2.1
       ;spam=-5
       ;spam-detail="Hormel-1.0;whitelist=-10,call_volume=5"
     Via: SIP/2.0/UDP sip.atlanta.com;branch=z9hG4bKfjzc
       ;received=192.0.3.2
       ;spam=-100
       ;spam-detail="Jaeger-3.3;not-a-spammer=-100"
     Max-Forwards: 70
     To: Bob <sip:bob@biloxi.com>
     From: Alice <sip:alice@atlanta.com>;tag=1928301774
     Call-ID: a84b4c76e66710@pc33.atlanta.com
     CSeq: 314159 INVITE
     Contact: <sip:alice@pc33.atlanta.com>
     Content-Type: application/sdp
     Content-Length: 142

                             Figure 2: example


6.  Security Considerations

   SIP proxies and SIP user agents need to ignore spam scores in Via
   headers generated by proxies that aren't trusted.  Via headers have
   the most recent proxy on top, so parsing for spam scores should stop
   at the first Via header from a non-trusted proxy.


7.  Acknowledgements

   Add your name here.


8.  IANA Considerations

   This document will add new IANA registrations for new SIP headers.

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



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   document.]]


9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, 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,
              June 2002.

9.2.  Informational References

   [I-D.ietf-sipping-spam]
              Rosenberg, J. and C. Jennings, "The Session Initiation
              Protocol (SIP) and Spam", draft-ietf-sipping-spam-05 (work
              in progress), July 2007.

   [I-D.tschofenig-sipping-framework-spit-reduction]
              Tschofenig, H., "A Framework to tackle Spam and Unwanted
              Communication for Internet  Telephony",
              draft-tschofenig-sipping-framework-spit-reduction-01 (work
              in progress), July 2007.


Authors' Addresses

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

   Email:  dwing@cisco.com













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   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


   Hannes Tschofenig
   Nokia Siemens Networks
   Otto-Hahn-Ring 6
   Munich, Bavaria  81739
   Germany

   Email:  Hannes.Tschofenig@nsn.com


   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






















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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
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Acknowledgment

   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).





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