SIPPING Working Group M. Garcia-Martin
Internet-Draft Ericsson
Expires: April 11, 2003 October 11, 2002
3rd-Generation Partnership Project (3GPP) Release 5 requirements on
the Session Initiation Protocol (SIP)
draft-ietf-sipping-3gpp-r5-requirements-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
The 3rd Generation Partnership Project (3GPP) has selected SIP [2]as
the session establishment protocol for the 3GPP IP Multimedia Core
Network Subsystem (IMS). IMS is part of the Release 5 of the 3GPP
specifications. Although SIP is a protocol that fulfills most of the
requirements to establish a session in an IP network, SIP has never
been evaluated against the specific 3GPP requirements for operation
in a cellular network. In this document we express the requirements
identified by 3GPP to support SIP for the Release 5 of the 3GPP IMS
in cellular networks.
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Table of Contents
1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 5
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview of the 3GPP IMS . . . . . . . . . . . . . . . . . 5
4. 3GPP Requirements on SIP . . . . . . . . . . . . . . . . . 8
4.1 General requirements . . . . . . . . . . . . . . . . . . . 8
4.1.1 Efficient use of the radio interface . . . . . . . . . . . 8
4.1.2 Minimum session setup time . . . . . . . . . . . . . . . . 8
4.1.3 Minimum support required in the terminal . . . . . . . . . 8
4.1.4 Roaming and non-roaming . . . . . . . . . . . . . . . . . 8
4.1.5 Terminal mobility management . . . . . . . . . . . . . . . 8
4.1.6 IP version 6 . . . . . . . . . . . . . . . . . . . . . . . 9
4.2 SIP outbound proxy . . . . . . . . . . . . . . . . . . . . 9
4.2.1 SIP outbound proxy . . . . . . . . . . . . . . . . . . . . 9
4.2.2 Discovery of the SIP outbound proxy . . . . . . . . . . . 9
4.3 Registration . . . . . . . . . . . . . . . . . . . . . . . 9
4.3.1 Registration required . . . . . . . . . . . . . . . . . . 10
4.3.2 Location of the SIP Registrar . . . . . . . . . . . . . . 10
4.3.3 Efficient registration . . . . . . . . . . . . . . . . . . 10
4.3.4 Registration for roaming and non-roaming cases . . . . . . 10
4.3.5 Visited domain name . . . . . . . . . . . . . . . . . . . 10
4.3.6 De-registration . . . . . . . . . . . . . . . . . . . . . 11
4.4 SIP Compression . . . . . . . . . . . . . . . . . . . . . 12
4.4.1 Compression algorithm independency . . . . . . . . . . . . 12
4.4.2 Extensibility of the SIP compression . . . . . . . . . . . 12
4.4.3 Minimal impact of SIP compression on the network . . . . . 12
4.4.4 Optionality of SIP compression . . . . . . . . . . . . . . 13
4.5 QoS requirements related to SIP . . . . . . . . . . . . . 13
4.5.1 Independence between QoS signaling and SIP . . . . . . . . 13
4.5.2 Coordination between SIP and QoS/Resource allocation . . . 13
4.6 Prevention of theft of service . . . . . . . . . . . . . . 14
4.7 Radio resource authorization . . . . . . . . . . . . . . . 14
4.8 Prevention of malicious usage . . . . . . . . . . . . . . 14
4.9 Prevention of denial of service . . . . . . . . . . . . . 15
4.10 Identification of users . . . . . . . . . . . . . . . . . 15
4.10.1 Private user identity . . . . . . . . . . . . . . . . . . 15
4.10.2 Public user identities . . . . . . . . . . . . . . . . . . 15
4.10.3 Delivery of the dialed public user ID . . . . . . . . . . 17
4.11 Identifiers used for routing . . . . . . . . . . . . . . . 17
4.12 Hiding requirements . . . . . . . . . . . . . . . . . . . 17
4.12.1 Hiding of the network structure . . . . . . . . . . . . . 17
4.12.2 Hiding of IP addresses . . . . . . . . . . . . . . . . . . 17
4.12.3 SIP hiding proxy . . . . . . . . . . . . . . . . . . . . . 18
4.13 Cell-ID . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.13.1 Cell-ID in signaling from the UA to the visited and home
networks . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.13.2 Format of the cell-ID . . . . . . . . . . . . . . . . . . 18
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4.14 Release of sessions . . . . . . . . . . . . . . . . . . . 18
4.14.1 Ungraceful session release . . . . . . . . . . . . . . . . 19
4.14.2 Graceful session release . . . . . . . . . . . . . . . . . 19
4.15 Routing of SIP messages . . . . . . . . . . . . . . . . . 19
4.15.1 SIP outbound proxy . . . . . . . . . . . . . . . . . . . . 20
4.15.2 SIP serving proxy in the home network . . . . . . . . . . 20
4.15.3 INVITE might follow a different path than REGISTER . . . . 20
4.15.4 SIP inbound proxy . . . . . . . . . . . . . . . . . . . . 20
4.15.5 Distribution of the Source Routing set of proxies . . . . 20
4.16 Emergency sessions . . . . . . . . . . . . . . . . . . . . 21
4.17 Identities used for session establishment . . . . . . . . 21
4.17.1 Remote Party Identification presentation . . . . . . . . . 21
4.17.2 Remote Party Identification privacy . . . . . . . . . . . 21
4.17.3 Remote Party Identification blocking . . . . . . . . . . . 21
4.17.4 Anonymity . . . . . . . . . . . . . . . . . . . . . . . . 22
4.17.5 Anonymous session establishment . . . . . . . . . . . . . 22
4.18 Charging . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.18.1 Support of both prepaid and postpaid models . . . . . . . 22
4.18.2 Charging correlation levels . . . . . . . . . . . . . . . 23
4.18.3 Charging correlation principles . . . . . . . . . . . . . 23
4.18.4 Collection of Session Detailed Information . . . . . . . . 24
4.19 General support of additional capabilities . . . . . . . . 24
4.19.1 Additional capabilities . . . . . . . . . . . . . . . . . 24
4.19.2 DTMF signaling . . . . . . . . . . . . . . . . . . . . . . 24
4.19.3 Early Media . . . . . . . . . . . . . . . . . . . . . . . 25
4.20 Exchange of session description . . . . . . . . . . . . . 25
4.21 Prohibition of certain SDP parameters . . . . . . . . . . 25
4.21.1 Prohibition of codecs . . . . . . . . . . . . . . . . . . 25
4.21.2 Prohibition of media types . . . . . . . . . . . . . . . . 26
4.22 Network initiated re-authentication . . . . . . . . . . . 26
4.23 Security model . . . . . . . . . . . . . . . . . . . . . . 26
4.24 Access Domain Security . . . . . . . . . . . . . . . . . . 27
4.24.1 General requirements . . . . . . . . . . . . . . . . . . . 27
4.24.2 Authentication . . . . . . . . . . . . . . . . . . . . . . 29
4.24.3 Message Protection . . . . . . . . . . . . . . . . . . . . 29
4.24.4 Negotiation of mechanisms . . . . . . . . . . . . . . . . 30
4.24.5 Verification of messages . . . . . . . . . . . . . . . . . 31
4.25 Network Domain Security . . . . . . . . . . . . . . . . . 31
5. Security considerations . . . . . . . . . . . . . . . . . 32
6. IANA considerations . . . . . . . . . . . . . . . . . . . 32
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . 32
Normative References . . . . . . . . . . . . . . . . . . . 32
Informational References . . . . . . . . . . . . . . . . . 33
Author's Address . . . . . . . . . . . . . . . . . . . . . 35
Full Copyright Statement . . . . . . . . . . . . . . . . . 36
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1. Conventions
This document does not specify any protocol of any kind. Therefore,
the usage of the key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
"OPTIONAL" in this document, as described in RFC-2119 [1], does not
apply.
2. Introduction
3GPP has selected SIP [2]as the protocol to establish and tear down
multimedia sessions in the IP Multimedia Subsystem (IMS). A
description of the IMS can be found in 3GPP Technical Specification
23.228 [31]. A comprehensive set of session flows can be found in
3GPP Technical Specification 24.228 [32].
This document is an effort to define the requirements applicable to
the usage of the SIP protocol suite in cellular networks, and
particularly in the 3GPP IMS, and in particular, to the Release 5 of
the 3GPP specifications. Further releases of the 3GPP specifications
may contain additional requirements to SIP. This document focuses on
the requirements identified for the 3GPP Release 5 IMS.
The rest of this document is structured as follows:
o Section 3 offers an overview of the 3GPP IMS. Readers who are not
familiar with it should carefully read this section.
o Section 4 contains the 3GPP requirements to SIP. Requirements are
grouped by categories. Some requirements include a statement on
possible solutions that would be able to fulfill the requirement.
Note also that, as a particular requirement might be fulfilled by
different solutions, not all the solutions might have an impact on
SIP.
3. Overview of the 3GPP IMS
This section gives the reader an overview of the 3GPP IM CN Subsystem
(IMS). It is not intended to be comprehensive. But it provides
enough information to understand the basis of the 3GPP IMS. Readers
are encouraged to find a more detailed description in the 3GPP
Technical Specifications 23.060 [30], 23.228 [31] and 24.228 [32].
For a particular cellular device, the 3GPP IMS network is further
decomposed in a home network and a visited network.
An IMS subscriber belongs to his or her home network. Services are
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triggered and may be executed in the home network. One or more SIP
servers are deployed in the SIP home network to support the IP
Multimedia Subsystem. Among those SIP servers, there is a SIP
serving proxy, which is also acting as a SIP registrar.
Authentication/Authorization servers may be part of the home network
as well. Users are authenticated in the home network.
A SIP outbound proxy is provided to support the UA. The SIP outbound
proxy is typically located in the visited network, although it may
located in the home network as well. The SIP outbound proxy
maintains security associations between itself and the terminals, and
interworks with the resource management in the packet network.
The SIP outbound proxy is assigned after the mobile device has
connected to the access network. Once this proxy is assigned, it
does not change while the mobile remains connected to the access
network. Thus the mobile can move freely within the access network
without SIP outbound proxy reassignment.
The home network may support also one or more SIP edge proxies.
These nodes may act as the first entry point for SIP signaling to the
home network and may decide (with the help of location servers) which
SIP registrar server to assign to a particular user. Typically the
address of the home network SIP edge proxy is configured in DNS in
the form of a DNS NAPTR and SRV records for SIP.
Additionally, home and visited networks may deploy, if required, a
SIP hiding proxy. The main purpose of the SIP hiding proxy is to
hide the network configuration.
The 3GPP IM CN Subsystem is designed to be access independent.
Access is granted from 3GPP cellular terminals or from other
terminals that use other accesses out of the scope of 3GPP.
3GPP cellular IP Multimedia terminals use the existing General Packet
Radio Service (GPRS) [30] as a transport network for IP datagrams.
The terminals first connect to the GPRS network to get an IPv6
prefix. In order to do this, the terminals must perform a (GPRS)
Attach procedure followed by a (GPRS) PDP Context Activation
procedure. These GPRS procedures are required to be completed before
any IP Multimedia session can be established.
As a result of the above-mentioned GPRS procedures, the terminal has
built an IPv6 address. The IPv6 address belongs to the same network
address space as the SIP outbound proxy. The address does not change
as the mobile terminal moves while still attached to the same network
address space.
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If the terminal moves from a GPRS access to another GPRS access, the
above-mentioned GPRS procedures needs to start from the beginning to
allocate an IPv6 address to the terminal.
Figure 1 shows an overview of the 3GPP architecture for IM CN
Subsystem.
+-------------+ +----------------+ +----------------+
| | | | | +------+ |
| | | | | | SIP | |
| | | | | |server| |
| | | | | | +------+ |
+-|+ | | | | | / |
| | | | | +------+ | | +------+ |
| | | | | | SIP | | | | SIP | |
| | ---|-------------|--|----|server|----|---|-|server| |
+--+ | | | +------+ | | +------+ |
| | | | | |
SIP | GPRS access | | Visited Network| | Home Network |
dev. +-------------+ +----------------+ +----------------+
Figure 1: Overview of the 3GPP IMS architecture
Another possible future configuration is depicted in Figure 2. In
that case, a general-purpose computer (e.g., a laptop computer) is
connected to a GPRS terminal. The computer hosts the Multimedia
application (comprising SIP, SDP, RTP, etc.). The GPRS terminal
handles the radio access and the GPRS connectivity. Note that, for
the sake of clarity, in this example the home network has not been
depicted in the figure.
+-------------+ +----------------+
+-------+ | | | | |
| | +-|+ | | | |
| | | | | | | +------+ |
+-------+ | | | | | | SIP | |
/ / --------| | ---|-------------|-------|server|------
/-------/ +--+ | | | +------+ |
| | | |
SIP GPRS | GPRS access | | Visited Network|
client terminal +-------------+ +----------------+
Figure 2: A computer connected to a GPRS terminal
Services are typically executed in an application server. The
interface between the SIP server and the application server is based
on SIP. However, certain operators may want to reuse the existing
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technology, and therefore, they may need to interoperate SIP with
protocols like CAMEL/Intelligent-Network or Open services
Architecture (OSA).
4. 3GPP Requirements on SIP
4.1 General requirements
This section does not specify any particular requirement to SIP.
However, it includes a list of general requirements that must be
considered when developing solutions to particular requirements.
4.1.1 Efficient use of the radio interface
The radio interface is a scarce resource. As such, the exchange of
signaling messages between the mobile terminal and the network should
be minimized. All the mechanisms developed should make an efficient
use of the radio interface.
See also the related requirements in Section 4.4
4.1.2 Minimum session setup time
All the procedures and mechanisms should have a minimum impact on the
session setup time as perceived by the user. When there is a choice
between performing tasks at session establishment and in transactions
prior to session establishment, then the tasks should be performed
prior to session establishment.
See also the related requirements in Section 4.4
4.1.3 Minimum support required in the terminal
As terminals could be rather small devices, memory requirements,
power consumption, processing power, etc. should be kept to a
minimum. Mandating support for additional protocols in the terminal
must meet this requirement.
4.1.4 Roaming and non-roaming
All the requirements must be met for both roaming and non-roaming
scenarios. There should not be a significant change in the signaling
procedures between roaming and non-roaming scenarios.
4.1.5 Terminal mobility management
As terminal mobility is managed by the access network, there is no
need to support terminal mobility management in SIP.
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4.1.6 IP version 6
3GPP IMS is solely designed to use IP version 6. As a consequence,
all protocols must support IPv6 addesses.
4.2 SIP outbound proxy
4.2.1 SIP outbound proxy
A SIP outbound proxy is provided to support both roaming and non-
roaming scenarios. The SIP outbound proxy may be located either in
the home network or in the visited network.
4.2.2 Discovery of the SIP outbound proxy
There must be a general mechanism so that the mobile device (UA)
learns the SIP outbound proxy address.
The Internet Draft DHCPv6 option for SIP servers [22] seems to
fulfill the requirement.
In addition to the above expressed requirement, the 3GPP access
network may provide the SIP outbound proxy address during access
network bearer establishment. This is considered a less general
mechanism though.
4.3 Registration
The home network must maintain one or more SIP registrars. The SIP
registrar authenticates the user and registers the IP address where
the user can be located.
Once the terminal is switched on, the mobile device UA reads its
configuration data. This data may be stored in a SIM card or any
other memory device. The configuration data contains an
identification of the home network. The device finds the SIP
registrar address from the home network domain name. The terminal
sends the registration through the SIP outbound proxy.
In order to support the search of the registrar, the home network
contains one or more SIP servers that may be configured in DNS with
the NAPTR/SRV record of SIP. These are the home network edge
proxies. Their mission is to serve as a first point of contact in
the home network, and decide (with the help of location servers)
which SIP registrar server to assign to a particular user.
The procedures specified in RFC 3263 [11] applied to a REGISTER
message seems to be sufficient to meet this requirement.
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4.3.1 Registration required
A user must register to the IMS before he/she can receive any
invitation to any sessions. In addition, it is desirable for the
user to register before initiating any sessions. The rationale
behind this is that:
1. The SIP serving proxy in the home network needs to know when the
user is available and from which terminal, in order to route
received SIP requests for sessions and services.
2. The user can be pre-authenticated early, so that authentication
does not contribute to post-dial delay. The procedure should not
have a penalty on the session setup time (see also the
requirement stated in Section 4.1.2).
3. The user is assigned a particular serving proxy. The serving
proxy downloads the service profile for that user to trigger
services.
Therefore, 3GPP has mandated the mobile device UA to register before
the mobile device UA initiates any session.
4.3.2 Location of the SIP Registrar
4.3.3 Efficient registration
Due to the scarce radio interface resource, a single registration
must be sufficient to insure that the mobile UA is reachable from
both the home and visited networks.
A single REGISTER message, addressed to the registrar, may traverse
the SIP outbound proxy. This can install, if needed, soft
registration states in the SIP outbound proxy.
4.3.4 Registration for roaming and non-roaming cases
Independently of whether the UA is roaming or not, it is desirable
for the registration procedure to be the same.
4.3.5 Visited domain name
The home network must be able to validate the existence of a roaming
agreement between the home and the visited network. The home network
needs to validate that the user is allowed to roam to such a visited
network. Therefore, there must be a mechanism so that the visited
network identity is known at registration time at the home network.
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It is acceptable to represent the visited network identity either as
a visited network domain name or as a string.
4.3.6 De-registration
4.3.6.1 De-registration of users
There must be a procedure for a user to de-register from the network.
This procedure may be used, e.g., when the user deactivates the
terminal.
We believe that a REGISTER with an expiration timer of 0 will meet
the requirement.
4.3.6.2 Network initiated de-registration or re-registration
There are a number of situations where the network needs to de-
register or trigger a re-registration of a previously registered UA.
Examples of usage are described in Section 4.3.6.3, Section 4.3.6.4
and Section 4.3.6.5.
This implies a need for a notification mechanism whereby the UA can
be notified of the de-registration, or a request for re-registration.
We believe this requirement is met by the SIP-specific event
notification [13] and a registration event package [16].
4.3.6.3 Network initiated de-registration, network maintenance
There might be cases when the SIP serving proxy has to shutdown,
e.g., due to maintenance operation. Although this situation is not
likely to happen in everyday situations, still it is desirable to
have a mechanism to inform the UA that his current registration is
being cancelled. The UA may initiate another registration process,
that will lead to the selection of a new SIP serving proxy.
4.3.6.4 Network initiated de-registration, network/traffic determined
The system must support a mechanism to avoid inconsistent information
storage and remove any redundant registration information. This case
will occur when a subscriber roams to a different network without a
prior de-registration. This case occurs in normal mobility
procedures when the user roams from one access network to another
one, or when imposing new service conditions to roamers.
4.3.6.5 Network initiated de-registration, administrative
For different reasons (e.g., subscription termination, stolen
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terminal, etc.) a home network administrative function may determine
a need to clear a user's SIP registration. It is desirable to have a
mechanism whereby the SIP serving proxy can inform the UA that his
registration is being cancelled.
There must be a procedure for a the SIP serving proxy to de-register
users. The de-registration information must be available at all the
proxies that keep registration state and the UA.
We believe that a procedure based on SIP-specific event notification
[13] and a registration event package [16].
4.4 SIP Compression
The radio interface is a scarce resource and typically, the available
bandwidth over the radio interface is limited. These two factors
seem to limit the transport of possibly large SIP messages over the
air interface. Particularly, the session setup time might be
extended, due to the time needed to transport SIP messages over a
limited bandwidth channel.
On the other hand, the number and size of certain SIP header values,
such as Via or Record-Route, seems to not be limited. A mobile
device UA may present limitations in the available memory to store
this kind of information.
Therefore, there must be a mechanism to efficiently transport SIP
signaling packets over the radio interface, by compressing the SIP
messages between the mobile device UA and the SIP outbound proxy, and
between the SIP outbound proxy and the mobile device UA. Note that
compression of IP and transport layer protocol headers that carry
these SIP messages is also a requirement, although we believe that
does not have an impact on SIP.
4.4.1 Compression algorithm independency
The chosen solution(s) must be able to allow the operation under
several different compression algorithms.
4.4.2 Extensibility of the SIP compression
The chosen solution(s) must be extensible to facilitate the
incorporation of new and improved compression algorithms in a
backward compatible way, as they become available.
4.4.3 Minimal impact of SIP compression on the network
Application specific compression must minimize impacts on existing
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3GPP access networks (such as base stations transceivers). On the
other hand, the compression mechanism should be independent of the
access, e.g., the compression must be defined between the mobile
device UA and the outbound SIP proxy.
4.4.4 Optionality of SIP compression
It must be possible to leave the usage of compression for SIP
signaling optional. To facilitate mobile terminal roaming between
networks which are using compression, the mobile terminal should
always support ability to compress SIP signaling. If compression is
not supported, communication may continue without compression,
depending on the local policy of the visited network.
4.4.4.1 Compression reliability
The compression mechanism should be reliable and be able to recover
automatically from errors generated during the decompression.
4.5 QoS requirements related to SIP
4.5.1 Independence between QoS signaling and SIP
The selection of QoS signaling and resource allocation schemes must
be independent of the selected session control protocols. This
allows for independent evolution of QoS control and SIP.
4.5.2 Coordination between SIP and QoS/Resource allocation
4.5.2.1 Allocation before alerting
In establishing a SIP session, it must be possible for an application
to request that the resources needed for bearer establishment are
successfully allocated before the destination user is alerted. Note,
however, that it must be also possible for an SIP application in a
terminal to alert the user before the radio resources are established
(e.g., if the user wants to participate in the media negotiation).
We believe this requirement is met by Integration of Resource
Management and SIP [17].
4.5.2.2 Destination user participates in the bearer negotiation
In establishing a SIP session, it must be possible for a terminating
application to allow the destination user to participate in
determining which bearers shall be established. Although it must be
possible to establish the SIP session without user intervention.
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We believe this requirement is met by the standard SDP negotiation
described in SIP [2] and the SDP offer/answer model [12] and the
extensions described in Integration of Resource Management and SIP
[17].
4.5.2.3 Successful bearer establishment
Successful bearer establishment must include the completion of any
required end-to-end QoS signaling, negotiation and resource
allocation.
We believe this requirement is met by the procedures described in the
Integration of Resource Management and SIP [17] .
4.6 Prevention of theft of service
Users are typically allocated QoS resources. There is an admission
control mechanism that prevents users to exceeds the limits
negotiated with the network. The network must prevent unauthorized
users to make usage of non-authorized resources. For instance, the
network must provide mechanism to prevent a user to use the resources
allocated to a second user, and for which this second user may be
paying.
We believe this requirement may be met by the procedures described in
the Private SIP extensions for Media Authorization [18].
4.7 Radio resource authorization
As radio resources are very valuable the network must be able to
manage these in a controlled manner. The network must be able to
identify who is using these resources and be able to authorize their
usage. For example, a mobile device terminal could execute an
unlimited and uncontrolled resorce reservation procedure if the
network does not supervise the usage of radio resources.
We believe this requirement is met by the procedures described in the
Private SIP extensions for Media Authorization [18]..
4.8 Prevention of malicious usage
The 3GPP IMS must prevent mobile devices for making a malicious usage
of the network. For instance, a malicious UA could not follow the
Record-Route procedures, so that subsequent request bypass proxies
which recorded route.
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4.9 Prevention of denial of service
The risk of a proxy to receive a denial of service attack shall be
minimized. For instance, a malicious mobile device could learn a SIP
proxy IP address and port number (e.g., in a Record-Route header
value) and establish an attack to that proxy.
4.10 Identification of users
4.10.1 Private user identity
In order to use the 3GPP IMS, a user is assigned a private user
identity. The home network operator assigns the private user
identity, which is used to uniquely identify the user from a network
perspective. The private user identity is used, for example, for
authentication, authorization, administration, and possibly
accounting purposes. Note that the private user identity is not used
for routing of SIP messages.
The private user identity is a unique global identity defined by the
Home Network Operator. The identity takes the form of a Network
Access Identifier (NAI) as defined in RFC 2486 [7].
The end user does not have access to the private user identity.
Typically the identity is stored in a Subscriber Identity Module
card.
The private user identity is permanently allocated to a user (it is
not a dynamic identity), and is valid for the duration of the user's
business subscription with the home network.
4.10.1.1 Private user ID in registrations
The mobile UA must deliver the private user identity to the SIP
outbound proxy and the registrar at registration time.
The private user identity is used as the basis for authentication
during registration of the mobile user. The term authentication is
used in this document with the same meaning as it is defined in RFC
2828 [8].
We believe that this requirement is met by populating the username
field of the Authorization: header value of the REGISTER request with
the private user identity.
4.10.2 Public user identities
In order to use the 3GPP IMS, a user is assigned one or more public
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user identities. The user will make use of the public user identity/
identities when requesting communication to other users. For
example, the public user identity might be included on a business
card.
Different public user identities may be grouped into a user profile.
A user may have different profiles, each one containing different
public user identities. A public user identity can be part of a
single user profile.
The user may need to register one or more public user identities
prior to receiving communications addressed to that public user
identity.
We believe this requirement is met by populating the From: and To:
header values of a REGISTER message with the public user identity.
4.10.2.1 Format of the public user identities
The public user identity/identities must take the form of a SIP URI
(as defined in RFC 3261 [2] and RFC 2396 [4]) or the form of a E.164
[37]number.
We believe this requirement is met by using SIP URLs and telephone
numbers represented in SIP URLs as described in SIP [3]. In
addition, tel: URLs as specified in [13] can be used to fulfill the
requirement.
4.10.2.2 Registration of public user IDs
It must be possible to register globally (i.e., through one single UA
request) a user that has more than one public identity that belongs
to the same user profile, via a mechanism within the IMS. In this
case, the user will be registered with all the public identities
associated to a user profile.
We believe this requirement may be accomplished by external
procedures. For example, the user's profile may contain a list of
alias identities that the registrar considers active if the primary
identity is registered. The user may get informed of the
automatically registered public user IDs by subscribing to its own
registration state.
4.10.2.3 Authentication of the public user ID
Public user identities are not authenticated by the 3GPP IMS.
However the network authorizes that the public user identity is
associated to the registered private user identity.
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There is a list of public user identities that are associated with
each private user ID within the IMS. IMS will reject attempts to use
other public identities with this private user ID.
4.10.3 Delivery of the dialed public user ID
Typically a UA will be registered under a set of different public
user IDs. As such, sessions destined to the user can be placed to
any of the registered public user IDs. The serving proxy,
application server(s) in the termination network may apply certain
filtering rules or services based on the public user ID contained in
the Request-URI. The UA may also apply certain filtering rules or
services based on the called public user ID.
As such, it must be possible, for all sessions, to deliver the dialed
public user ID to the terminating entities, such as the serving
proxy, application servers and the terminating UA.
4.11 Identifiers used for routing
Routing of SIP signaling within IMS must use SIP URLs as defined in
SIP [2]. E.164 [37] format public user identities must not be used
for routing within IMS, and session requests based upon E.164 format
public user identities will require conversion into SIP URI format
for internal IMS usage.
We believe that this requirement is achieved by translating E.164
numbers into SIP URIs. A database, such as ENUM [10] might do the
job.
4.12 Hiding requirements
Although the requirements included in this section are not optional,
the hiding feature is an optional to use through configuration. This
means that a network operator can, at his desire, switch the hiding
functionality on or off.
4.12.1 Hiding of the network structure
A network operator need not be required to reveal the internal
network structure to another network (in Via, Route, or other
headers) that may contain indication of the number of SIP proxies,
domain name of the SIP proxies, capabilities of the SIP proxies or
capacity of the network.
4.12.2 Hiding of IP addresses
A network need not be required to expose the explicit IP addresses of
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the nodes within the network (excluding firewalls and border
gateways).
4.12.3 SIP hiding proxy
In order to support the hiding requirements, a SIP hiding proxy may
be included in the SIP signaling path. Such additional proxy may be
used to shield the internal structure of a network from other
networks.
4.13 Cell-ID
The identity of the cell through which the 3GPP UA is accessing the
IMS (Cell-ID) may be used by the home network to provide localized
services or information on the location of the terminal during an
emergency call (when emergency calls are handled in IMS, see also the
requirement stated in Section 4.16).
4.13.1 Cell-ID in signaling from the UA to the visited and home networks
Assuming that the Cell-ID is obtained by the UA by other mechanisms
outside the scope or beyond SIP, the Cell-ID must be transported at
least in the following procedures:
o Registration
o Session Establishment (Mobile Originated)
o Session Establishment (Mobile Terminated)
o Session Release
The Cell-ID is private information and only of interest in the UA
home network. Therefore, the Cell-ID should be removed prior to
sending the SIP signaling beyond the originating home network.
4.13.2 Format of the cell-ID
The cell-ID must be sent in any of the formats described in the 3GPP
Technical Specification 23.003 [29].
4.14 Release of sessions
In addition to the normal mechanisms to release a SIP session (e.g.,
BYE), two cases are considered in this section. The ungraceful
release of the session (e.g., the terminal moves to an out-of-
coverage zone) and the graceful session release ordered by the
network (e.g., pre-paid caller runs out of credit).
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We believe this requirement is met by a SIP entity acting as a so-
called transparent back-to-back User Agent.
4.14.1 Ungraceful session release
If an ungraceful session termination occurs (e.g., flat battery or
mobile leaves coverage), when a call stateful SIP proxy server (such
as the SIP serving proxy at home) is involved in a session, memory
leaks and eventually server failure can occur due to hanging state
machines. To ensure stable server operation and carrier grade
service, a mechanism to handle the ungraceful session termination
issue must be provided. We assume that there is a mechanism by which
the SIP outbound proxy is notified, by a mechanism external to SIP,
of the ungraceful session termination. This allows transforming the
ungraceful session release into a graceful session release ordered by
the network (see next section). For example, the SIP outbound proxy,
upon reception of the notification of loss of mobile radio coverage,
could send a BYE request on behalf of the terminal, although this BYE
cannot be authenticated.
4.14.2 Graceful session release
There must be a mechanism so that an entity in the network may order
the release of resources to other entities. This may be used, e.g.,
in pre-paid calls when the user runs out of credit.
This release must not involve any request to the UA to send out a
release request (BYE), as the UA might not follow this request. The
receiving entity needs the guarantee that resources are released when
requested by the ordering entity.
The following objectives must be met:
o Accurately report the termination to the charging subsystem.
o Release the associated network resources: bearer resources and
signaling resources.
o Notify other parties to the session, if any, of the session
termination.
Where feasible, this mechanism should be at the SIP protocol level in
order to guarantee access independence for the system.
4.15 Routing of SIP messages
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4.15.1 SIP outbound proxy
The 3GPP architecture includes a SIP outbound proxy which is
typically located in the visited network (although it may be located
in the home network). This outbound proxy provides local services
such as compression of SIP messages or security functions. In
addition, the outbound proxy may interact with the media reservation
mechanism to provide authentication and authorization support for
media reservation.
All mobile terminal originated session setup attempts must transit
the outbound proxy, so that the services provided by the outbound
proxy can be delivered to the mobile terminal.
4.15.2 SIP serving proxy in the home network
The serving proxy in the home network allows triggering of user
customized services that are typically executed in an application
server.
All mobile terminal originated session setup attempts must transit
the serving proxy in the home network, so that the proxy can properly
trigger the SIP services allocated to the user(e.g., speed dial
substitution). This implies a requirement for some sort of source-
routing mechanism to assure these proxies are transited correctly.
4.15.3 INVITE might follow a different path than REGISTER
The path taken by an INVITE request need not be restricted to the
specific path taken by a mobile terminal originated REGISTER request,
e.g., the INVITE may traverse just the SIP outbound proxy and the SIP
serving proxy, without passing through any other proxies. However,
the path taken by the INVITE may follow the same path taken by the
REGISTER .
4.15.4 SIP inbound proxy
The visited network may apply certain services and policies to
incoming sessions (such as establishment of security services or
interaction with the media reservation mechanism). Therefore, the
visited network may contain a SIP inbound proxy for terminating
sessions. In general, the SIP inbound proxy and the SIP outbound
proxy are the same SIP proxy.
4.15.5 Distribution of the Source Routing set of proxies
Section 4.15.2 and Section 4.15.4 assume that a source routing
mechanism is used to effect traversal of the required SIP proxies
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during session setup.
There must be some means of dynamically informing the node which adds
the source routing set of proxies that the INVITE has to traverse
(e.g., the outbound proxy or serving proxy) of what that set of
proxies should be.
The hiding requirements expressed in Section 4.12 also apply to the
said set of proxies.
4.16 Emergency sessions
3GPP networks already contain alternative procedures to deliver
emergency sessions. The Release 5 of the 3GPP specifications does
not add any requirement with respect SIP emergency sessions.
4.17 Identities used for session establishment
4.17.1 Remote Party Identification presentation
It must be possible to present to the caller the identity of the
party to which he/she may dial back to return a call.
We believe this requirement is met by the procedures described in
draft-ietf-sip-asserted-identity [19].
4.17.2 Remote Party Identification privacy
In addition to the previous requirement, the called party must be
able to request that his/her identity not be revealed to the caller.
We believe this requirement is met by the procedures described in
draft-ietf-sip-privacy-general [20].
4.17.3 Remote Party Identification blocking
Regulatory agencies, as well as subscribers, may require the ability
of a caller to block the display of their caller identification.
This function may be performed by the destination subscriber's SIP
serving proxy. In this way, the destination subscriber is still able
to do a session-return, session-trace, transfer, or any other
supplementary service.
Therefore, it must be possible that the caller requests to block the
display of his/her identity at the callee's display.
We believe this requirement is met by the procedures described in
draft-ietf-sip-privacy-general [20].
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4.17.4 Anonymity
Procedures are required for an anonymous session establishment.
However, sessions are not intended to be anonymous to the originating
or terminating network operators.
We believe this requirement is met by the procedures described in
draft-ietf-sip-privacy-general [20] and draft-ietf-sip-asserted-
identity [19].
4.17.5 Anonymous session establishment
If the caller requests the session to be anonymous, the UAC must not
reveal any identity information to the UAS.
If the caller requests the session to be anonymous, the terminating
network must not reveal any identity or signaling routing information
to the destination endpoint. The terminating network should
distinguish at least two cases, first if the caller intended the
session to be anonymous, and second if the caller's identity was
deleted by a transit network.
We believe this requirement is met by the procedures described in
draft-ietf-sip-privacy-general [20] and draft-ietf-sip-asserted-
identity [19].
4.18 Charging
The 3GPP charging implications are described in the 3GPP Technical
Specification 32.225 [34].
4.18.1 Support of both prepaid and postpaid models
Operators may choose to offer prepaid and/or postpaid services. The
prepaid model is accomplished with the support of the on-line
charging model. The postpaid model is accomplished by the support of
the off-line charging model.
On-line charging is the process where charging information can
affect, in real-time, the service rendered to the user, such as
request for a graceful release of an existing session. On-line
charging interacts with the SIP signaling.
Off-line charging is the process where charging information does not
affect, in real-time, the service rendered to the user.
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4.18.2 Charging correlation levels
The following levels of correlation for IMS charging are considered:
o Correlation within a session. A session may comprise a number of
media components. It must be possible to correlate the charging
data of the different media components belonging to a session.
o Correlation at media component level. For a session comprising
several media types (such as audio and video), charging data is
generated for each media type and needs to be correlated between
network elements. For this, a media identifier shall be unique
and shall clearly identify to which media type of a session this
charging information belongs to. This component identifier is not
exchanged between network elements and is based on the ordering of
media flows in the SDP. This ordering is the same as the one used
in the binding information passed to the GPRS network.
4.18.3 Charging correlation principles
To support the correlation of charging information, the following
principles apply to both offline and online charging:
o The correlation of charging information for an IMS session is
based on the use of IMS Charging Identifiers (ICID).
o The first IMS network entity within the SIP signaling path is
responsible for assigning an ICID. This ICID shall then be passed
along the whole session path in an end-to-end manner. However,
this shall not preclude further elements (other SIP proxies) along
the session path generating additional identifiers to be passed
along.
o The ICID is passed to all IMS network entities in the session
signaling path. This is performed using SIP signaling.
o The addresses of the charging functions are passed by the serving
SIP proxy to all IMS network entities in the session signaling
path. This is to provide a common destination for all the
charging records generated by each IMS network entity with the
same ICID.
o For the charging correlation between the GPRS network and the IMS,
one or more GPRS Charging IDs, which identify the PDP contexts of
the session, are passed from the GPRS network to the IMS.
o The GPRS Charging IDs are passed by the outbound SIP proxy to the
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serving SIP proxy and the Application Servers using SIP signaling.
They are not transferred from one home IMS (e.g., caller's home)
to another home IMS (e.g., callee's home).
o Inter Operator Identifiers (IOI) are shared betweenthe caller's
home IMS and the callee's home IMS to provide identifiers of the
home originating and home terminating networks.
4.18.4 Collection of Session Detailed Information
The SIP serving proxy or another SIP server in the home network must
be able to log details of all sessions, such as the duration, source,
and destination of a session, to provide to the charging subsystem.
4.19 General support of additional capabilities
4.19.1 Additional capabilities
3GPP is interested on applying and using additional services, like
those described in SIP Call Control - Transfer [23], SIP Basic Call
Flow Examples [24], SIP PSTN Call Flows [25] and SIP service examples
[26]. Although 3GPP is not going to standardize additional services,
3GPP may make sure that the capabilities that enable those services
are granted in the network.
As such we believe that the SIP REFER method [27] and the Replaces
header [28] constitute a complement to be used as an enabler in order
to meet the above requirement.
4.19.2 DTMF signaling
Support for voice calls must provide a similar level of service to
the existing circuit based voice service. This includes the ability
to utilize DTMF signaling e.g., for control of interactive voice
response systems such as ticket sales lines, timetable information
etc.
The transport of DTMF tones from the mobile terminal to target
systems that may be in the PSTN, or to SIP based solutions (i.e., no
PSTN connection) must be supported.
The transport of DTMF signals may be required for the whole call,
just for the first part, or from some later point in the call, i.e.,
the start time and duration of such signaling is unpredictable.
We believe that the mechanisms specified in RFC 2833 [9] meet the
requirement without impacting SIP.
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4.19.3 Early Media
As mobile terminals will frequently interoperate with the PSTN,
support for early media is required.
4.20 Exchange of session description
Typically a session description protocol like SDP is used in SIP to
describe the media streams and codecs needed to establish the
session. SIP uses an offer/answer model of the session description,
as described in RFC 3264 [12] where one of the parties offers his
session description and the other answers to that offer.
In the 3GPP IMS, the mobile terminals might have restrictions with
the memory, DSP capacity, etc. As such, it is required a mechanism
by which the Session Description negotiation may conclude with one
out of many codecs per media stream. Both UAC and UAS must know,
prior to any media is sent or received, which codec is used for each
media stream.
In the 3GPP IMS, an efficient use of the network and radio resources
is an important requirement. As such, the network should know in
advance which codecs is used for a particular media stream. The
network access control may use this information to grant access to
the network and control the resource utilization.
Additionally, it is required that the party who pays for the resource
utilization has the opportunity to decide the codecs to use, once
both end parties are aware of the capabilities supported at the
remote UA.
Therefore, it is required a mechanism by which both UAC and UAS have
the ability to negotiate and trim down the number of codecs used per
media stream, so that at the end of the negotiation there can be a
reduced set of agreed codecs per media stream.
We believe that the mechanism specified in RFC 3264 [12] meet the
requirement.
4.21 Prohibition of certain SDP parameters
4.21.1 Prohibition of codecs
The SIP outbound proxy may contain local policy rules with respect
the codecs allowed in the network. For instance, certain networks
may disallow high bandwidth consuming audio codecs. There has to be
a mechanism whereby the SIP outbound proxy can reject a session
establishment attempt when a codec is prohibited in the network due
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to local policy.
4.21.2 Prohibition of media types
Certain user's subscription may include restrictions to use certain
media types. For instance, a user may not be allowed to establish a
video session. The SIP serving proxy in the home network downloads
the user profile, which contains the rules of this kind of
restrictions.
As the establishment of sessions traverse the SIP serving proxy in
the home network, this proxy can prohibit an attempt to establish a
session that includes a non-allowed media type for the user.
Therefore, there has to be a mechanism whereby the SIP serving proxy
can reject a session establishment attempt when the session includes
a forbidden media type.
4.22 Network initiated re-authentication
Network operators need to authenticate users to ensure that they are
charged appropriately for the services they use. The re-
authentication done when the user initiates a message will not
suffice for this purpose, as described below.
If the duration of the authentication period is set to a relatively
low value to ensure that the user cannot incur a high amount of
charges between two authentications, it may create a lot of
unnecessary authentications of users which have remained largely
inactive, and therefore utilize unnecessary air interface resources.
If the duration of the authentication period is set to a relatively
high value to avoid these unnecessary authentications the risk is
then that some users may incur high charges between authentications.
A user's authentication is automatically invalidated when a certain
threshold for charges (or number, or duration of sessions) is reached
without giving the user a chance to re-authenticate, even if a valid
registration exists. This would not provide an adequate level of
service.
Consequently it must be possible for the network to initiate a re-
authentication process at any time. The triggers must be set within
the network and may include charging thresholds, number of events,
session duration etc.
4.23 Security model
Section 4.23, Section 4.24 and Section 4.25 have been based on the
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3GPP Technical Specifications 33.203 [35], 23.228 [31] and 33.210
[36].
The scope for security of the 3GPP IMS is securing the SIP signaling
between the various SIP entities. Protecting the end-to-end media
streams may be a future extension but is not considered in the
Release 5 version of the IMS specifications.
Each operator providing IMS services acts as its own domain of trust,
and shares a long-term security association with its subscribers
(e.g., pre-shared keys). Operators may enter into roaming agreements
with other operators, in which case a certain level of trust exists
between their respective domains.
SIP user agents must authenticate to their home network before the
use of IMS resources is authorized. In the Release 5 of the 3GPP IMS
specifications, authentication is performed during registration and
re-registrations.
Portions of the SIP signaling must be protected hop-by-hop. Looking
at Figure 1 in Section 3, we can distinguish two distinct zones where
the required security is unique:
o Access Domain: Between the SIP user device and the visited
network.
o Network Domain: Between the visited and the home networks, or
inside the home network.
Characteristics needed in the Access Domain are quite different from
those of the Network Domain because the terminal's requirements on
mobility, computation restriction, battery limit, bandwidth
conservation and radio interface. SIP entities in the access domain
should be able to maintain security contexts with a large group of
users in parallel. Furthermore, Access Domain provides user specific
security associations while Network Domain provides security
associations between network nodes. Therefore the weight of
protocols and algorithms and the compliance of them with compression
mechanisms are very important to Access Domain Security. It is
therefore required that the security solutions must allow different
mechanisms in these two domains.
4.24 Access Domain Security
4.24.1 General requirements
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4.24.1.1 Scalability and Efficiency
3GPP IMS is characterized by a large subscriber base of up to a
billion users, all of which must be treated in a secure manner.
The security solutions must allow global roaming among a large number
of administrative domains.
4.24.1.2 Bandwidth and Roundtrips
The wireless interface in 3GPP terminals is an expensive resource
both in terms of power consumption and maximum utilization of scarce
spectrum. Furthermore, cellular networks have typically long round-
trip time delays, which must be taken in account in the design of the
security solutions.
Any security mechanism that involves 3GPP terminals should not
unnecessarily increase the bandwidth needs.
All security mechanisms that involve 3GPP terminals should minimize
the number of necessary extra roundtrips. In particular, during
normal call signaling there should not be any additional security
related messages.
For example, once an IPsec security association or a TLS connection
is established, no additional round trips are required during session
setup. However, the requirement of minimizing the number of round
trips is hard to satisfy with IKE or TLS. It seems that IKE [6] adds
a number of roundtrips, particularly if run together with legacy
authentication extensions developed in the IPSRA WG. TLS [3] uses
fewer roundtrips, but on the other hand doesn't support UDP.
4.24.1.3 Computation
It must be possible for mobile device terminals to provide security
without requiring public key cryptography and/or certificates. 3GPP
IMS may, however, include optional security schemes that employ these
techniques.
Current HTTP authentication methods use only symmetric cryptography
as required here. Lower-layer mechanisms (ex: IKE, TLS) require
implementation of public-key cryptography and/or Diffie-Helman. If
these lower-layer mechanisms were used, the mobile terminal would
authenticate and negotiate session keys with the visited network
using only symmetric methods.
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4.24.1.4 Independence of the transport protocol
The selected security mechanism should work with any transport
protocol allowed by SIP (e.g., TCP, UDP).
4.24.2 Authentication
Authentication, as used in this context, means entity authentication
that enables two entities to verify the identity of the respective
peer.
4.24.2.1 Authentication method
A strong, mutual authentication must be provided.
The authentication method must be able to work when there are zero or
more SIP proxies in the SIP path between the authenticator and the
authenticated user.
It must be possible to support extensible authentication methods.
Therefore authentication using an extensible authentication framework
is strongly recommended.
Authentication methods based on the secure storage of long-term keys
used for authentication and the secure execution of authentication
algorithms must be supported.
The SIP client's credentials must not be transferred as plain text.
3GPP intends to reuse UMTS AKA [15]. UMTS AKA applies a symmetric
cryptographic scheme, provides mutual authentication, and is
typically implemented on a so-called SIM card that provides secure
storage on the user's side.
Additional requirements related to message protection that apply to
the authentication method are stated in Section 4.24.3.
4.24.3 Message Protection
4.24.3.1 Message Protection Mechanisms
SIP entities (typically a SIP client and a SIP proxy) must be able to
communicate using integrity and replay protection. By integrity, we
mean the ability for receiver of a message to verify that the message
has not been modified in transit. SIP entities should be able to
communicate confidentially. In 3GPP IMS, these protection modes must
be based on initial authentication. Integrity protection and
confidentiality must be possible using symmetric cryptographic keys.
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It must be possible to handle also error conditions in a satisfactory
manner as to allow recovery (see also Section 4.3.6.3 and Section
4.14).
It must be possible to provide this protection between two adjacent
SIP entities. In future network scenarios it may also be necessary
to provide this protection through proxies, though the 3GPP Release 5
IMS does not require this.
The security mechanism must be able to protect a complete SIP
message.
If header compression/removal or SIP compression is applied to SIP
messages, it must be compatible with message protection.
4.24.3.2 Delegation
3GPP IMS implements distributed security functions responsible for
authentication and message protection.
It must be possible to perform an initial authentication based on
long-term authentication credentials, followed by subsequent
protected signaling that uses short-term authentication credentials,
such as session keys created during initial authentication. The used
authentication mechanism is able to provide such session keys. It
must be possible to apply subsequent message protection as soon as
possible, even during the initial authentication period.
Initial authentication is performed between the SIP UA and the
authenticating SIP serving proxy in the home network. However, the
authentication mechanism must not require access to the long-term
authentication credentials in these nodes. In the home network, the
authenticating SIP serving proxy must support interaction with a
dedicated authentication server in order to accomplish the
authentication task. At the client side a secured (tamper-resistant)
device storing the long-term credentials of the user must perform the
authentication.
Additionally, the SIP serving proxy that performed the initial
authentication must be able to securely delegate subsequent SIP
signaling protection (e.g., session keys for integrity or encryption)
to an authorized SIP proxy further downstream. The tamper-resistant
device at the client side must be able to securely delegate the
session keys to the SIP user agent.
4.24.4 Negotiation of mechanisms
A method must be provided to securely negotiate the security
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mechanisms to be used in the access domain.
This method must at least support the negotiation of different
security mechanisms providing integrity protection and encryption,
algorithms used within these mechanisms and additional parameters
they require to be exchanged.
The negotiation mechanism must protect against attackers who do not
have access to authentication credentials. In particular, the
negotiation mechanism must be able to detect a possible man-in-the-
middle attacker who could influence the negotiation result such that
services with weaker or no security are negotiated.
A negotiation mechanism is generally required in all secure protocols
to decide which security services to use and when they should be
started. This security mechanism serves algorithm and protocol
development as well as interoperability. Often, the negotiation is
handled within a security service. For example, the HTTP
authentication scheme includes a selection mechanism for choosing
among appropriate algorithms. Note that when referring to
negotiation we mean just the negotiation, not all functions in
protocols like IKE. For instance, we expect the session key
generation is to be a part of the initial authentication.
SIP entities must be able to use the same security mode parameters to
protect several SIP sessions without re-negotiation. For example,
security mode parameters may be assumed to be valid within the
lifetime of a registration. Note that it is necessary to amortize
the cost of security association setup and parameter negotiation over
several INVITEs.
4.24.5 Verification of messages
4.24.5.1 Verification at the SIP outbound proxy
The SIP outbound proxy must be able to guarantee the message origin
and verify that the message has not been changed (e.g., it is
integrity protected).
4.24.5.2 Verification at the SIP serving proxy
The serving SIP proxy needs to receive an indication if the outbound
proxy was able to verify the message origin and, in the case of a
REGISTER request, whether it was integrity protected or not.
4.25 Network Domain Security
Message authentication, key agreement, integrity and replay
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protection, and confidentiality must be provided for communications
between SIP network entities such as proxy servers.
Network domain security mechanisms must be scalable up to a large
number of network elements.
3GPP intends to make it mandatory to have the protection discussed
above at least between two operators, and optional within an
operator's own network. Security gateways exist between operator's
networks.
We believe the above requirements to be fulfilled by applying
security mechanisms as specified in the current IP Security standards
specified in RFC 2401 [5].
5. Security considerations
This document does not define a protocol, but still presents some
security requirements to protocols. The main security requirements
are stated in Section 4.23, Section 4.24 and Section 4.25.
Additional security-related issues are discussed under Section 4.6,
Section 4.7, Section 4.8, Section 4.9, Section 4.12 and Section 4.10.
6. IANA considerations
This document introduces no new IANA considerations.
7. Contributors
The following people contributed to this document:
Duncan Mills (Vodafone), Gabor Bajko (Nokia), Georg Mayer (Siemens),
Francois-Xerome Derome (Alcatel), Hugh Shieh (AWS), Andrew Allen
(dynamicsoft), Sunil Chotai (mmO2), Keith Drage (Lucent), Jayshree
Bharatia (Nortel), Kevan Hobbis (Huthison 3G UK), Dean Willis
(dynamicsoft), Krisztian Kiss (Nokia), Vesa Torvinen (Ericsson), Jari
Arkko (Ericsson), Sonia Garapaty (Nortel).
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] 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.
Informational References
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[3] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A. and
P. Kocher, "The TLS Protocol Version 1.0", RFC 2246, January
1999.
[4] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.
[5] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[6] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.
[7] Aboba, B. and M. Beadles, "The Network Access Identifier", RFC
2486, January 1999.
[8] Shirey, R., "Internet Security Glossary", RFC 2828, May 2000.
[9] Schulzrinne, H. and S. Petrack, "RTP Payload for DTMF Digits,
Telephony Tones and Telephony Signals", RFC 2833, May 2000.
[10] Faltstrom, P., "E.164 number and DNS", RFC 2916, September
2000.
[11] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[12] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[13] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[14] Olson, S., Camarillo, G. and A. Roach, "Support for IPv6 in
Session Description Protocol (SDP)", RFC 3266, June 2002.
[15] Niemi, A., Arkko, J. and V. Torvinen, "Hypertext Transfer
Protocol (HTTP) Digest Authentication Using Authentication and
Key Agreement (AKA)", RFC 3310, September 2002.
[16] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Registrations", draft-rosenberg-sip-reg-00 (work in
progress), May 2002.
[17] Rosenberg, J., Camarillo, G. and F. Andreasen, "Integration of
Resource Management and SIP", draft-ietf-sip-manyfolks-
resource-07 (work in progress), April 2002.
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[18] Evans, D., Marshall, W. and F. Andreasen, "SIP Extensions for
Media Authorization", draft-ietf-sip-call-auth-06 (work in
progress), May 2002.
[19] Watson, M., Peterson, J. and C. Jennings, "Private Extensions
to the Session Initiation Protocol (SIP) for Asserted Identity
within Trusted Networks", draft-ietf-sip-asserted-identity-02
(work in progress), August 2002.
[20] Peterson, J., "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", draft-ietf-sip-privacy-general-01 (work in
progress), June 2002.
[21] Droms, R., Perkins, C., Bound, J., Volz, B., Carney, M. and T.
Lemon, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
draft-ietf-dhc-dhcpv6-26 (work in progress), June 2002.
[22] Volz, B. and H. Schulzrinne, "DHCPv6 Options for SIP Servers",
draft-ietf-sip-dhcpv6-00 (work in progress), April 2002.
[23] Sparks, R., "SIP Call Control - Transfer", draft-ietf-sip-cc-
transfer-05 (work in progress), May 2002.
[24] Johnston, A., "Session Initiation Protocol Basic Call Flow
Examples", draft-ietf-sipping-basic-call-flows-01 (work in
progress), October 2002.
[25] Johnston, A., "Session Initiation Protocol PSTN Call Flows",
draft-ietf-sipping-pstn-call-flows-00 (work in progress),
August 2002.
[26] Johnston, A., "SIP Service Examples", draft-ietf-sipping-
service-examples-02 (work in progress), July 2002.
[27] Sparks, R., "The SIP Refer Method", draft-ietf-sip-refer-06
(work in progress), July 2002.
[28] Dean, R., Biggs, B. and R. Mahy, "The Session Inititation
Protocol (SIP) 'Replaces' Header", draft-ietf-sip-replaces-02
(work in progress), May 2002.
[29] 3GPP, "TS 23.003 Numbering, addressing and identification
(Release 5)", September 2002, <ftp://ftp.3gpp.org/Specs/
archive/23_series/23.003/>.
[30] 3GPP, "TS 23.060:General Packet Radio Service (GRPS); Service
Description; Stage 2", September 2002, <ftp://ftp.3gpp.org/
Specs/archive/23_series/23.060/>.
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[31] 3GPP, "TS 23.228: IP Multimedia Subsystem (IMS) (Stage 2) -
Release 5", September 2002, <ftp://ftp.3gpp.org/Specs/archive/
23_series/23.228/>.
[32] 3GPP, "TS 24.228: Signaling flows for the IP Multimedia call
control based on SIP and SDP", September 2002, <ftp://
ftp.3gpp.org/Specs/archive/24_series/24.228/>.
[33] 3GPP, "TS 24.229: IP Multimedia Subsystem (IMS) (Stage 3) -
Release 5", September 2002, <ftp://ftp.3gpp.org/Specs/archive/
24_series/24.229/>.
[34] 3GPP, "TS 32.225: Telecommunication Management; Charging
Management; Charging Data Description for IP Multimedia
Subsystem; (Release 5)", September 2002, <ftp://ftp.3gpp.org/
Specs/archive/32_series/32.225/>.
[35] 3GPP, "TS 32.203: 3G Security; Access security for IP based
services; (Release 5)", September 2002, <ftp://ftp.3gpp.org/
Specs/archive/33_series/33.203/>.
[37] ITU-T, "Recommendation E.164 (05/97): The international public
telecommunication numbering plan", May 1997, <http://
www.itu.int/rec/
recommendation.asp?type=folders&lang=e&parent=T-REC-E.164>.
Author's Address
Miguel A. Garcia Martin
Ericsson
Hirsalantie 11
Jorvas FIN-02420
Finland
EMail: miguel.a.garcia@ericsson.com
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Full Copyright Statement
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