SIPPING Working Group G. Camarillo
Internet-Draft G. Blanco
Expires: August 5, 2005 Ericsson
February 2005
The Session Initiation Protocol (SIP) P-User-Database Private-Header
(P-Header)
draft-camarillo-sipping-user-database-01.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 5, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document specifies the SIP P-User-Database 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 address of the database that contains the user
profile of the user that generated a particular request.
Camarillo & Blanco Expires August 5, 2005 [Page 1]
Internet-Draft The P-User-Database P-Header February 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1 User Registering to the IMS . . . . . . . . . . . . . . . . 3
3.2 Incoming Request for an Unregistered User . . . . . . . . . 4
4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. P-User-Database header field Definition . . . . . . . . . . . 5
6. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1 Normative References . . . . . . . . . . . . . . . . . . . 6
10.2 Informational References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
Camarillo & Blanco Expires August 5, 2005 [Page 2]
Internet-Draft The P-User-Database P-Header February 2005
1. Introduction
The 3rd-Generation Partnership Project (3GPP) IMS (IP Multimedia
Subsystem) uses SIP [3] as its main signalling protocol. 3GPP has
identified a set of requirements that can be met, according to the
procedures in RFC 3427 [4], by defining a new SIP P-header.
The remainder of this document is organized as follows. Section 2
defines the terminology used in this document. Section 3 describes
the scenarios considered by 3GPP and Section 4 discusses the
requirements derived from these scenarios. Section 5 defines the
P-User-Database header field, which meets those requirements, and
Section 6 discusses the applicability and scope of this new header
field. Section 7 registers the P-User-Database header field with the
IANA and Section 8 discusses the security properties of the
environment where this header field is intended to be used.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
3. Scenarios
In the 3GPP IMS, there are two scenarios where a set of proxies
handling a request need to consult the same user database. These
scenarios consist of a user registering to the IMS network and an
unregistered user receiving an incoming request that triggers a
service (e.g., a voice mail service).
3.1 User Registering to the IMS
In the 3GPP IMS, SIP REGISTER requests generated by a UA (User Agent)
traverse a set of SIP proxy servers before reaching the SIP
registrar. A REGISTER request sent by a UA is routed to the outbound
proxy of the UA, which is referred to as the P-CSCF (Proxy-Call/
Session Control Function).
The P-CSCF routes the REGISTER request to another proxy, which is
always located in the home domain of the user, which is referred to
as the I-CSCF (Interrogating-CSCF). The I-CSCF consults the user
database of the domain, which is referred to as the HSS (Home
Subscriber Server), in order to choose the registrar that will
process the REGISTER request.
Camarillo & Blanco Expires August 5, 2005 [Page 3]
Internet-Draft The P-User-Database P-Header February 2005
With the information received from the HSS, the I-CSCF routes the
REGISTER request to the appropriate registrar, which is referred to
as the S-CSCF (Serving-CSCF). At this point, the S-CSCF needs to
contact the same HSS that was previously contacted by the I-CSCF in
order to fetch the user profile of the user that generated the
REGISTER request.
The interface between the I-CSCF and the HSS and between the S-CSCF
and the HSS is called Cx interface, and it is based on Diameter [5].
When there is a single HSS (i.e., user database) handling all the
users in the domain, both the I-CSCF and the S-CSCF can be configured
with its address so that they contact it when necessary. However,
some domains have several HSSs, each of which handles a particular
set of users. When dealing with a REGISTER request, the I-CSCF and
the S-CSCF need to discover which is the HSS that contains the
profile of user that generated the REGISTER request.
In networks with more than one HSS, a Diameter redirect agent
referred to as SLF (Subscription Locator Function) is implemented.
The interface between the I-CSCF and the SLF and between the S-CSCF
and the SLF is called Dx interface and, like the CX interface, is
based on Diameter. The SLF provides the I-CSCF and the S-CSCF with
the address of the HSS that handles the user they are dealing with.
Therefore, in a network with more than one HSS, the SLF is consulted
twice per REGISTER request. First by the I-CSCF, and later by the
S-CSCF. If the I-CSCF could provide the S-CSCF with the address of
the HSS handling the user that generated the REGISTER request, the
S-CSCF could contact directly that HSS. That is, the S-CSCF would
not need to contact the SLF in order to obtain the address of the
HSS.
3.2 Incoming Request for an Unregistered User
In the 3GPP IMS, incoming requests for a user traverse an I-CSCF in
the home domain of the user. This I-CSCF consults the HSS, using the
Diameter-based Cx interface, in order to decide which S-CSCF should
handle the request. After consulting the HSS, the I-CSCF forwards
the request to a S-CSCF, which is also located in the home domain of
the user.
If the user the request is addressed to is registered to the IMS
network, the S-CSCF receiving the request knows which HSS handles the
user. The S-CSCF stored this information when the user registered.
However, if the user is not registered, the S-CSCF needs to consult
the SLF (assuming more than one HSS in the network) in order to
discover the HSS handling the user.
Camarillo & Blanco Expires August 5, 2005 [Page 4]
Internet-Draft The P-User-Database P-Header February 2005
Therefore, like in the previous scenario, in a network with more than
one HSS, the SLF is consulted twice per incoming request addresses to
an unregistered user. First by the I-CSCF, and later by the S-CSCF.
If the I-CSCF could provide the S-CSCF with the address of the HSS
handling the user that generated the request, the S-CSCF could
contact directly that HSS. That is, the S-CSCF would not need to
contact the SLF in order to obtain the address of the HSS.
4. Requirements
This section lists the requirements derived from the previous
scenarios:
1. It is necessary to optimize the registration process in the 3GPP
IMS by reducing the time it takes for a UA to register to the IMS
network.
2. It is necessary to optimize the handling of incoming requests to
unregistered users in the 3GPP IMS by reducing the time it takes
for a domain to handle these requests.
3. It is necessary to improve the scalability of SLFs in the 3GPP
IMS by reducing the amount of traffic the SLF of a network needs
to handle.
5. P-User-Database header field Definition
This document defines the SIP P-User-Database P-header. This header
field can be added to requests routed from an I-CSCF to a S-CSCF.
The P-User-Database P-header contains the address of the HSS handling
the user that generated the request.
The augmented Backus-Naur Form (BNF) [2] syntax of the P-User-
Database header field is the following:
P-User-Database = "P-User-Database" HCOLON database
database = LAQUOT DiameterURI RAQUOT
DiameterURI is defined in RFC 3588 [5]. HCOLON, LAQUOT, and RAQUOT
are defined in RFC 3261 [3].
The following is an example of a P-User-Database header field:
P-User-Database: <aaa://host.example.com;transport=tcp>
Camarillo & Blanco Expires August 5, 2005 [Page 5]
Internet-Draft The P-User-Database P-Header February 2005
6. Applicability
According to RFC 3427 [4], P-headers have a limited applicability.
Specifications on P-headers such as this document 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-User-Database header field is intended to be used in 3GPP IMS
networks. This header field carries the HSS's address between an
I-CSCF and a S-CSCF.
When SIP is used on the Internet, there are typically no proxies
querying a user database between the UA sending a REGISTER request
and the registrar. Consequently, the P-User-Database header field
does not seem useful in a general Internet environment.
7. IANA Considerations
This document defines a new SIP header field: P-User-Database. This
header field needs to be registered by the IANA in the SIP Parameters
registry under the Header Fields subregistry.
8. Security Considerations
The P-User-Database 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-User-Database
header field will be used ensures the integrity and the
confidentiality of the contents of this header field.
9. Acknowledgements
Nuria Esteban, Stephen Terrill, and Jeroen van Bemmel provided
comments on this document.
10. References
10.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
Camarillo & Blanco Expires August 5, 2005 [Page 6]
Internet-Draft The P-User-Database P-Header February 2005
[3] 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.
[4] 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.
[5] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
"Diameter Base Protocol", RFC 3588, September 2003.
[6] Camarillo, G., "The Internet Assigned Number Authority (IANA)
Uniform Resource Identifier (URI) Parameter Registry for the
Session Initiation Protocol (SIP)", BCP 99, RFC 3969,
December 2004.
10.2 Informational References
Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
German Blanco
Ericsson
Via de los Poblados 13
Madrid 28035
Spain
Email: german.blanco@ericsson.com
Camarillo & Blanco Expires August 5, 2005 [Page 7]
Internet-Draft The P-User-Database P-Header February 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Camarillo & Blanco Expires August 5, 2005 [Page 8]
