One document matched: draft-camarillo-sipping-user-database-00.txt
SIPPING Working Group G. Camarillo
Internet-Draft G. Blanco
Expires: August 12, 2005 Ericsson
February 11, 2005
The Session Initiation Protocol (SIP) P-User-Database Private-Header
(P-Header)
draft-camarillo-sipping-user-database-00.txt
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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.
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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 . . . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1 Normative References . . . . . . . . . . . . . . . . . . . . 7
10.2 Informational References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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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 and a
related parameter 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.
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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.
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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 (some of the
definitions are taken from RFC 3261 [3]):
P-User-Database = "P-User-Database" HCOLON user-database-host
*( SEMI user-database-param )
user-database-host = host
user-database-param = user-database-realm / generic-param
user-database-realm = "realm" EQUAL hostname
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
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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 host and, optionally,
the HSS's realm 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.
This document defines a parameter for the P-User-Database header
field: realm. This header field parameter needs to be registered by
the IANA in the "SIP/SIPS URI Parameters" subregistry, which is
located under the "Session Initiation Protocol (SIP) Parameters"
registry. The reference should appear in single-brackets, as
indicated in RFC 3969 [6]. The resulting entry should be:
Parameter Name Predefined Values Reference
-------------- ----------------- ---------
realm No [RFCxxxx]
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 and Stephen Terrill provided comments on this document.
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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.
[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
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