Rejecting Anonymous Requests in the Session Initiation Protocol (SIP)
RFC 5079
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RFC - Proposed Standard
(December 2007; No errata)
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2015-10-14
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draft-rosenberg-sipping-acr-code
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RFC 5079 (Proposed Standard)
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Cullen Jennings
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Network Working Group J. Rosenberg
Request for Comments: 5079 Cisco
Category: Standards Track December 2007
Rejecting Anonymous Requests in the Session Initiation Protocol (SIP)
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
The Session Initiation Protocol (SIP) allows for users to make
anonymous calls. However, users receiving such calls have the right
to reject them because they are anonymous. SIP has no way to
indicate to the caller that the reason for call rejection was that
the call was anonymous. Such an indication is useful to allow the
call to be retried without anonymity. This specification defines a
new SIP response code for this purpose.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Server Behavior . . . . . . . . . . . . . . . . . . . . . . . . 3
4. UAC Behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. 433 (Anonymity Disallowed) Definition . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . . 6
Rosenberg Standards Track [Page 1]
RFC 5079 ACR Response Code December 2007
1. Introduction
The Session Initiation Protocol (SIP) [RFC3261] allows for users to
make anonymous calls. In RFC 3261, this is done by including a From
header field whose display name has the value of "Anonymous".
Greater levels of anonymity were subsequently defined in [RFC3323],
which introduces the Privacy header field. The Privacy header field
allows a requesting User Agent (UA) to ask for various levels of
anonymity, including user level anonymity, header level anonymity,
and session level anonymity. [RFC3325] additionally defined the
P-Asserted-Identity header field, used to contain an asserted
identity. RFC 3325 also defined the 'id' value for the Privacy
header field, which is used to request the network to remove the
P-Asserted-Identity header field.
Though users need to be able to make anonymous calls, users that
receive such calls retain the right to reject the call because it is
anonymous. SIP does not provide a response code that allows the User
Agent Server (UAS), or a proxy acting on its behalf, to explicitly
indicate that the request was rejected because it was anonymous. The
closest response code is 403 (Forbidden), which doesn't convey a
specific reason. While it is possible to include a reason phrase in
a 403 response that indicates to the human user that the call was
rejected because it was anonymous, that reason phrase is not useful
for automata and cannot be interpreted by callers that speak a
different language. An indication that can be understood by an
automaton would allow for programmatic handling, including user
interface prompts, or conversion to equivalent error codes in the
Public Switched Telephone Network (PSTN) when the client is a
gateway.
To remedy this, this specification defines the 433 (Anonymity
Disallowed) response code.
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].
Rosenberg Standards Track [Page 2]
RFC 5079 ACR Response Code December 2007
3. Server Behavior
A server (generally acting on behalf of the called party, though this
need not be the case) MAY generate a 433 (Anonymity Disallowed)
response when it receives an anonymous request, and the server
refuses to fulfill the request because the requestor is anonymous. A
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