Network Working Group G. Camarillo
Request for Comments: 5002 G. Blanco
Category: Informational Ericsson
August 2007 The Session Initiation Protocol (SIP)
P-Profile-Key Private Header (P-Header)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
This document specifies the SIP P-Profile-Key P-header. This header
field is used in the 3rd-Generation Partnership Project (3GPP) IMS
(IP Multimedia Subsystem) to provide SIP registrars and SIP proxy
servers with the key of the profile corresponding to the destination
SIP URI of a particular SIP request.
Table of Contents
1. Introduction ....................................................22. Terminology .....................................................23. Scenario ........................................................24. Requirements ....................................................35. P-Profile-Key Header Field Definition ...........................36. Applicability ...................................................47. IANA Considerations .............................................48. Security Considerations .........................................59. Acknowledgements ................................................510. References .....................................................510.1. Normative References ......................................510.2. Informative References ....................................6
The 3rd-Generation Partnership Project (3GPP) IMS (IP Multimedia
Subsystem) uses SIP [RFC3261] as its main signalling protocol. (For
more information on the IMS, a detailed description can be found in
3GPP TS 23.228 [3GPP.23.228] and 3GPP TS 24.229 [3GPP.24.229]). 3GPP
has identified a set of requirements that can be met, according to
the procedures in [RFC3427], by defining a new SIP P-header.
The remainder of this document is organized as follows. Section 3
describes the scenario considered by 3GPP and Section 4 discusses the
requirements derived from this scenario. Section 5 defines the P-
Profile-Key header field, which meets those requirements, and Section
6 discusses the applicability and scope of this new header field.
Section 7 registers the P-Profile-Key header field with the IANA and
Section 8 discusses the security properties of the environment where
this header field is intended to be used.
HSS: Home Subscriber Server.
I-CSCF: Interrogating - Call/Session Control Function.
Public Service Identity:
A SIP URI that refers to a service instead of a user.
S-CSCF: Serving - Call/Session Control Function.
Wildcarded Public Service Identity:
A set of Public Service Identities that match a regular
expression and share the same profile.
In the 3GPP IMS, there are scenarios where a set of proxies handling
a request need to consult the same user database, as described in
[RFC4457]. Those proxies typically use the destination SIP URI of
the request as the key for their database queries. Nevertheless,
when a proxy handles a Wildcarded Public Service Identity, the key to
be used in its database query is not the destination SIP URI of the
request, but a regular expression instead.
Public Service Identities are SIP URIs that refer to services instead
of users. That is, they address a specific application in an
Application Server. Wildcarded Public Service Identities are a set
of Public Service Identities that match a regular expression and
share the same profile. For example, the Public Service Identities
'sip:firstname.lastname@example.org' and 'sip:email@example.com'
would match the Wildcarded Public Service Identity
'sip:firstname.lastname@example.org'. For a description of Wildcarded
Public Service Identities, see 3GPP TS 23.003 [3GPP.23.003].
When a proxy queries the user database for a Public Service Identity
for which there is no profile in the user database, the user database
needs to find its matching Wildcarded Public Service Identity. For
example, if the user database receives a query for
'sip:email@example.com', the user database needs to go through
all the Wildcarded Public Service Identity it has until it finds a
matching one; in this case, 'sip:firstname.lastname@example.org'. The
process to find a matching Wildcarded Public Service Identity can be
computationally expensive, time consuming, or both.
When two proxies query the user database for the same Public Service
Identity, which matches a Wildcarded Public Service Identity, the
user database needs to perform the matching process twice. Having to
perform that process twice can be avoided by having the first proxy
obtain the Wildcarded Public Service Identity from the user database
and transfer it, piggy-backed in the SIP message, to the second
proxy. This way, the second proxy can query the user database using
the Wildcarded Public Service Identity directly.
An alternative, but undesirable, solution would consist of having the
user database store every Public Service Identity and its matching
Wildcarded Public Service Identity. The scalability and
manageability properties of this approach are considerably worse than
those of the approach described earlier.
This section lists the requirements derived from the previous
1. It is necessary to optimize the response time for session
establishment in the 3GPP IMS.
2. It is necessary to keep the user database's size and maintenance
manageable (e.g., storing individual Public Service Identities
matching a Wildcarded Public Service Identity in the user
database is not believed to be an acceptable solution).
5. P-Profile-Key Header Field Definition
This document defines the SIP P-Profile-Key P-header. The P-
Profile-Key P-header contains the key to be used by a proxy to query
the user database for a given profile.
The augmented Backus-Naur Form (BNF) [RFC4234] syntax of the
P-Profile-Key header field is the following:
P-Profile-Key = "P-Profile-Key" HCOLON (name-addr / addr-spec)
*( SEMI generic-param )
The format of HCOLON, name-addr, addr-spec, and generic-param are
defined in [RFC3261]. The format of Wildcarded Public Service
Identities is defined in 3GPP TS 23.003 [3GPP.23.003]. They take the
form of Extended Regular Expressions (ERE) as defined in Chapter 9 of
IEEE 1003.1-2004 Part 1 [IEEE.1003.1-2004].
The following is an example of a P-Profile-Key header field that
contains a Wildcarded Public Service Identity:
According to [RFC3427], P-headers have a limited applicability.
Specifications of P-headers such as this RFC need to clearly document
the useful scope of the proposal, and explain its limitations and why
it is not suitable for the general use of SIP on the Internet.
The P-Profile-Key header field is intended to be used in 3GPP IMS
networks. This header field carries the key of a service profile,
that is stored in a user database referred to as HSS, between two
proxies, which are referred to as I-CSCF and S-CSCF. The I-CSCF and
the S-CSCF belong to the same administrative domain and share a
common frame of reference to the user database. The I-CSCF inserts
the P-Profile-Key header field into a SIP request and the S-CSCF
removes it before routing the request further. (For a description of
how an I-CSCF and an S-CSCF query the same user database for a single
request, see [RFC4457].)
Typically, when SIP is used on the Internet, there are not multiple
proxies with a trust relationship between them querying the same user
database. Consequently, the P-Profile-Key header field does not seem
useful in a general Internet environment.
7. IANA Considerations
This document defines a new SIP header field: P-Profile-Key. This
header field has been registered by the IANA in the SIP Parameters
registry under the Header Fields subregistry.
8. Security Considerations
The P-Profile-Key defined in this document is to be used in an
environment where elements are trusted and where attackers are not
supposed to have access to the protocol messages between those
elements. Traffic protection between network elements is sometimes
achieved by using IPsec and sometimes by physically protecting the
network. In any case, the environment where the P-Profile-Key header
field will be used ensures the integrity and the confidentiality of
the contents of this header field. The P-Profile-Key header field
MUST NOT be used in environments that do not have these
The P-Profile-Key header field needs to be integrity protected to
keep attackers from modifying its contents. An attacker able to
modify the contents of this header field could make the network apply
a different service than the one corresponding to the request
carrying the P-Profile-Key header field.
The contents of the P-Profile-Key field need to be kept confidential.
An attacker able to access the contents of this header field would
obtain certain knowledge about the way services are structured in a
Alf Heidermark and Timo Forsman provided input to this document.
Miguel Angel Garcia-Martin performed an expert review on this
document on behalf of the SIPPING working group. Jon Peterson
provided comments on this document.
10.1. Normative References
[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.
[RFC3427] Mankin, A., Bradner, S., Mahy, R., Willis, D.,
Ott, J., and B. Rosen, "Change Process for the
Session Initiation Protocol (SIP)", BCP 67, RFC
3427, December 2002.
[RFC4234] Crocker, D. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", RFC 4234, October
[3GPP.23.003] 3GPP, "Numbering, addressing and identification",
3GPP TS 23.003 3.15.0, October 2006.
[IEEE.1003.1-2004] "Standard for information technology - portable
operating system interface (POSIX). Base
definitions", IEEE 1003.1-2004, 2004.
10.2. Informative References
[RFC4457] Camarillo, G. and G. Blanco, "The Session
Initiation Protocol (SIP) P-User-Database
Private-Header (P-Header)", RFC 4457, April 2006.
[3GPP.23.228] 3GPP, "IP Multimedia Subsystem (IMS); Stage 2",
3GPP TS 23.228 5.15.0, June 2006.
[3GPP.24.229] 3GPP, "Internet Protocol (IP) multimedia call
control protocol based on Session Initiation
Protocol (SIP) and Session Description Protocol
(SDP); Stage 3", 3GPP TS 24.229 5.18.0, October
Via de los Poblados 13
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