One document matched: draft-wing-sipping-spam-score-01.txt
Differences from draft-wing-sipping-spam-score-00.txt
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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