Internet Engineering Task Force (IETF) D. Petrie
Request for Comments: 6080 SIPez LLC
Category: Standards Track S. Channabasappa, Ed.
ISSN: 2070-1721 CableLabs
March 2011
A Framework for Session Initiation Protocol User Agent Profile Delivery
Abstract
This document specifies a framework to enable configuration of
Session Initiation Protocol (SIP) user agents (UAs) in SIP
deployments. The framework provides a means to deliver profile data
that user agents need to be functional, automatically and with
minimal or no User and Administrative intervention. The framework
describes how SIP user agents can discover sources, request profiles,
and receive notifications related to profile modifications. As part
of this framework, a new SIP event package is defined for
notification of profile changes. The framework provides minimal data
retrieval options to ensure interoperability. The framework does not
include specification of the profile data within its scope.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6080.
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Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Without obtaining an adequate license from the person(s) controlling
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outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Reference Model . . . . . . . . . . . . . . . . . . . . . 6
3.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Profile Types . . . . . . . . . . . . . . . . . . . . . . 9
3.4. Profile Delivery Stages . . . . . . . . . . . . . . . . . 9
3.5. Supported Device Types . . . . . . . . . . . . . . . . . . 10
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. Simple Deployment Scenario . . . . . . . . . . . . . . . . 10
4.2. Devices Supporting Multiple Users from Different
Service Providers . . . . . . . . . . . . . . . . . . . . 12
5. Profile Delivery Framework . . . . . . . . . . . . . . . . . . 14
5.1. Profile Delivery Stages . . . . . . . . . . . . . . . . . 14
5.2. Securing Profile Delivery . . . . . . . . . . . . . . . . 22
5.3. Additional Considerations . . . . . . . . . . . . . . . . 24
5.4. Support for NATs . . . . . . . . . . . . . . . . . . . . . 33
6. Event Package Definition . . . . . . . . . . . . . . . . . . . 33
6.1. Event Package Name . . . . . . . . . . . . . . . . . . . . 33
6.2. Event Package Parameters . . . . . . . . . . . . . . . . . 33
6.3. SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . . 36
6.4. Subscription Duration . . . . . . . . . . . . . . . . . . 37
6.5. NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . . 37
6.6. Notifier Processing of SUBSCRIBE Requests . . . . . . . . 37
6.7. Notifier Generation of NOTIFY Requests . . . . . . . . . . 38
6.8. Subscriber Processing of NOTIFY Requests . . . . . . . . . 38
6.9. Handling of Forked Requests . . . . . . . . . . . . . . . 39
6.10. Rate of Notifications . . . . . . . . . . . . . . . . . . 39
6.11. State Agents . . . . . . . . . . . . . . . . . . . . . . . 39
7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.1. Example 1: Device Requesting Profile . . . . . . . . . . . 39
7.2. Example 2: Device Obtaining Change Notification . . . . . 42
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46
8.1. SIP Event Package . . . . . . . . . . . . . . . . . . . . 46
8.2. Registry of SIP Configuration Profile Types . . . . . . . 46
9. Security Considerations . . . . . . . . . . . . . . . . . . . 47
9.1. Local-Network Profile . . . . . . . . . . . . . . . . . . 48
9.2. Device Profile . . . . . . . . . . . . . . . . . . . . . . 49
9.3. User Profile . . . . . . . . . . . . . . . . . . . . . . . 50
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 51
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 52
11.1. Normative References . . . . . . . . . . . . . . . . . . . 52
11.2. Informative References . . . . . . . . . . . . . . . . . . 53
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1. Introduction
SIP user agents require configuration data to function properly.
Examples include information specific to local networks, devices, and
users. A configuration data set specific to an entity is termed a
profile. For example, device profile contains the configuration data
related to a device. The process of providing devices with one or
more profiles is termed "profile delivery". Ideally, this profile
delivery process should be automatic and require minimal or no user
intervention.
Many deployments of SIP user agents require dynamic configuration and
cannot rely on pre-configuration. This framework provides a standard
means of providing dynamic configuration that simplifies deployments
containing SIP user agents from multiple vendors. This framework
also addresses change notifications when profiles change. However,
the framework does not define the content or format of the profile,
leaving that to future standardization activities.
This document is organized as follows. The normative requirements
are contained in Section 5 (framework operations) and Section 6 (the
event package definition). The rest of the document provides
introductory and supporting explanations. Section 3 provides a high-
level overview of the abstract components, profiles, and the profile
delivery stages. Section 4 provides some motivating use cases.
Section 7 follows with illustrative examples of the framework in use.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This document also reuses the SIP terminology defined in [RFC3261]
and [RFC3265], and it specifies the usage of the following terms.
Device: software or hardware entity containing one or more SIP user
agents. It may also contain applications such as a DHCP client.
Device Provider: the entity responsible for managing a given device.
Local Network Provider: the entity that controls the local network
to which a given device is connected.
SIP Service Provider: the entity providing SIP services to users.
This can refer to private or public enterprises.
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Profile: configuration data set specific to an entity (e.g., user,
device, local network, or other).
Profile Type: a particular category of profile data (e.g., user,
device, local network, or other).
Profile Delivery Server (PDS): the source of a profile, it is the
logical collection of the Profile Notification Component (PNC) and
the Profile Content Component (PCC).
Profile Notification Component (PNC): the logical component of a
Profile Delivery Server that is responsible for enrolling devices
and providing profile notifications.
Profile Content Component (PCC): the logical component of a Profile
Delivery Server that is responsible for storing, providing access
to, and accepting profile content.
Profile Delivery Stages: the processes that lead a device to obtain
profile data, and any subsequent changes, are collectively called
profile delivery stages.
Bootstrapping: Bootstrapping is the process by which a new (or
factory reset) device, with no configuration or minimal "factory"
pre-configuration, enrolls with the PDS. The device may use a
temporary identity and credentials to authenticate itself to
enroll and receive profiles, which may provide more permanent
identities and credentials for future enrollments.
3. Overview
This section provides an overview of the configuration framework. It
presents the reference model, the motivation, the profile delivery
stages, and a mapping of the concepts to specific use cases. It is
meant to serve as a reference section for the document, rather than
providing a specific logical flow of material, and it may be
necessary to revisit these sections for a complete appreciation of
the framework.
The SIP UA Profile Delivery Framework uses a combination of SIP event
messages (SUBSCRIBE and NOTIFY; [RFC3265]) and traditional file
retrieval protocols, such as HTTP [RFC2616], to discover, monitor,
and retrieve configuration profiles. The framework defines three
types of profiles (local-network, device, and user) in order to
separate aspects of the configuration that may be independently
managed by different administrative domains. The initial SUBSCRIBE
message for each profile allows the UA to describe itself (both its
implementation and the identity requesting the profile), while
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requesting access to a profile by type, without prior knowledge of
the profile name or location. Discovery mechanisms are specified to
help the UA form the Subscription URI (the Request-URI for the SIP
SUBSCRIBE). The SIP User Agent Server (UAS) handling these
subscriptions is the Profile Delivery Server (PDS). When the PDS
accepts a subscription, it sends a NOTIFY to the device. The initial
NOTIFY from the PDS for each profile may contain profile data or a
reference to the location of the profile, to be retrieved using HTTP
or similar file retrieval protocols. By maintaining a subscription
to each profile, the UA will receive additional NOTIFY messages if
the profile is later changed. These may contain a new profile, a
reference to a new profile, or a description of profile changes,
depending on the Content-Type [RFC3261] in use by the subscription.
The framework describes the mechanisms for obtaining three different
profile types, but does not describe the data model they utilize (the
data model is out of scope for this specification).
3.1. Reference Model
The design of the framework was the result of a careful analysis to
identify the configuration needs of a wide range of SIP deployments.
As such, the reference model provides for a great deal of
flexibility, while breaking down the interactions to their basic
forms, which can be reused in many different scenarios.
The reference model for the framework defines the interactions
between the Profile Delivery Server (PDS) and the device. The device
needs the profile data to function effectively in the network. The
PDS is responsible for responding to device requests and providing
the profile data. The reference model is illustrated in Figure 1.
+-------------------------+
+--------+ | Profile Delivery Server |
| Device |<==========================>| +---+ +---+ |
+--------+ | |PNC| |PCC| |
| +---+ +---+ |
+-------------------------+
PNC = Profile Notification Component
PCC = Profile Content Component
Figure 1: Framework Reference Model
The PDS is subdivided into two logical components:
o Profile Notification Component (PNC), responsible for enrolling
devices for profiles and providing profile change notifications.
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o Profile Content Component (PCC), responsible for storing,
providing access to, and accepting modifications related to
profile content.
3.2. Motivation
The motivation for the framework can be demonstrated by applying the
reference model presented in Section 3.1 to two scenarios that are
representative of the two ends of a spectrum of potential SIP
deployments.
In the simplest deployment scenario, a device connects through a
network that is controlled by a single provider who provides the
local network, manages the devices, and offers services to the users.
The provider propagates profile data to the device that contains all
the necessary information to obtain services in the network
(including information related to the local network and the users).
This is illustrated in Figure 2. An example is a simple enterprise
network that supports SIP-based devices.
--------------
/ Local Network, \
| Device & Service |
\ Provider /
----------------
|
|
--------
| Device |
--------
|
|
----
|User|
----
Figure 2: Simple Deployment Model
In more complex deployments, devices connect via a local network that
is not controlled by the SIP service provider, such as devices that
connect via available public WiFi hot spots. In such cases, local
network providers may wish to provide local network information such
as bandwidth constraints to the devices.
Devices may also be controlled by device providers that are
independent of the SIP service provider who provides user services,
such as kiosks that allow users to access services from remote
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locations. In such cases, the profile data may have to be obtained
from different profile sources: local network provider, device
provider, and SIP service provider. This is indicated in Figure 3.
--------
/ SIP \
| Service | -> Provides 'user' profile
| Provider | data (e.g., services
\ / configuration)
-------- --------
| / \
| | Device | -> Provides 'device' profile
| | Provider | data (e.g., device specifics)
| \ /
| ---------
| /
| / -------
| / / Local \
| / | Network |
| | | Provider | -> Provides 'local-network' profile
| | \ / data (e.g., bandwidth)
| | -------
| | /
| | /
| | |
===================
( Local Network )
===================
|
|
--------
| Device | -> Needs the 'local-network'
-------- and 'device' profile
/ \
/ \
------ ------
|User A| |User B| -> Users need 'user' profiles
------ ------
Figure 3: Complex Deployment Model
In either case, Providers need to deliver to the device, profile data
that is required to participate in their network. Examples of
profile data include the list of codecs that can be used and the SIP
proxies to which to connect for services. Pre-configuration of such
information is one option if the device is always served by the same
set of Providers. In all other cases, the profile delivery needs to
be automated and consistent across Providers. Given the presence of
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a number of large deployments where pre-configuration is neither
desired nor optimal, there is a need for a common configuration
framework such as the one described in this document.
Further, the former deployment model can be accomplished by the
device obtaining profile data from a single provider. However, the
latter deployment model requires the device to obtain profile data
from different providers. To address either deployment or any
variation in between, one needs to allow for profile delivery via one
or more Providers. The framework accomplishes this by specifying
multiple profile types and a set of profile delivery stages to obtain
them. These are introduced in the subsections to follow.
3.3. Profile Types
The framework handles the presence of potentially different Providers
by allowing for multiple profile types. Clients request each profile
separately, and obtain them from the same, or different, Providers.
A deployment can also choose to pre-configure the device to request
only a subset of the specified profile types. The framework
specifies three basic profile types, as follows:
Local Network Profile: contains configuration data related to the
local network to which a device is directly connected, provided by
the local network provider.
Device Profile: contains configuration data related to a specific
device, provided by the device provider.
User Profile: contains configuration data related to a specific
User, as required to reflect that user's preferences and the
particular services to which it is subscribed. It is provided by
the SIP service provider.
Additional profile types may also be specified by future work within
the IETF. The data models associated with each profile type are
out of scope for this document.
3.4. Profile Delivery Stages
The framework specified in this document requires a device to
explicitly request profiles. It also requires one or more PDSs,
which provide the profile data. The processes that lead a device to
obtain profile data, and any subsequent changes, can be explained in
three stages, termed the profile delivery stages.
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Profile Enrollment: the process by which a device requests, and if
successful, enrolls with a PDS capable of providing a profile. A
successful enrollment is indicated by a notification containing
the profile information (contents or content indirection
information). Depending on the request, this could also result in
a subscription to notification of profile changes.
Profile Content Retrieval: the process by which a device retrieves
profile contents, if the profile enrollment resulted in content
indirection information.
Profile Change Notification: the process by which a device is
notified of any changes to an enrolled profile. This may provide
the device with modified profile data or content indirection
information.
3.5. Supported Device Types
The examples in this framework tend to associate devices with
entities that are accessible to end-users. However, this is not
necessarily the only type of device that can utilize the specified
framework. Devices can be entities such as SIP Phones or soft
clients, with or without user interfaces (that allow for device
configuration), entities in the network that do not directly
communicate with any users (e.g., gateways, media servers, etc.) or
network infrastructure elements (e.g., SIP servers). The framework
is extensible for use with such device types. However, it is to be
noted that some of these other device types (e.g., network elements)
may also be configurable using other mechanisms. The use of this
framework in conjunction with other mechanisms (specified outside of
this document), is out of scope.
4. Use Cases
This section provides a small, non-comprehensive set of
representative use cases to further illustrate how this framework can
be utilized in SIP deployments. The first use case is simplistic in
nature, whereas the second is relatively complex. The use cases
illustrate the effectiveness of the framework in either scenario.
For security considerations, please refer to Sections 5 and 9.
4.1. Simple Deployment Scenario
Description: Consider a deployment scenario (e.g., a small private
enterprise) where a participating device implements this framework
and is configured, using previously obtained profile data, to request
only the device profile. Assume that the device operates in the same
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network as the PDS (i.e., there is no NAT) and it obtains its IP
configuration using DHCP. Typical communication between the device
and the PDS will traverse one or more SIP proxies, but is not
required, and is omitted in this illustration.
Figure 4 illustrates the sequence of events that includes device
start-up and a successful profile enrollment for the device profile
that results in device profile data. It then illustrates how a
change in the profile data is delivered via Profile Change
Notification.
+----------------------+
+--------+ | Provider's Network |
| Device | | |
| | | |
+--------+ | DHCP PDS |
+----------------------+
| | |
(A) |<============== DHCP =============>| |
| |
| |
| |
(B) |<=========== Profile Enrollment ============>|
| | Profile data
| | is modified
| |
(C) |<============ Profile Change ================|
| Notification |
| |
| |
Figure 4: Use Case 1
The following is an explanation of the interactions in Figure 4.
(A) Upon initialization, the device obtains IP configuration
parameters such as an IP address using DHCP.
(B) The device requests profile enrollment for the device profile.
Successful enrollment provides it with a notification containing
the device profile data.
(C) Due to a modification of the device profile, a profile change
notification is sent across to the device, along with the
modified profile.
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4.2. Devices Supporting Multiple Users from Different Service Providers
Description: Consider a single device that allows multiple users to
obtain services from different SIP service providers, e.g., a kiosk
at an airport.
The following assumptions apply:
o Provider A is the device and local network provider for the
device, and the SIP service provider for user A; Provider B is the
SIP service provider for user B.
o Profile enrollment always results in content indirection
information requiring profile content retrieval.
o Communication between the device and the PDSs is facilitated via
one or more SIP proxies (only one is shown in the illustration).
Figure 5 illustrates the use case and highlights the communications
relevant to the framework specified in this document.
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User User
A B +----------------------+ +----------------------+
+--------+ | Provider | | Provider |
| Device | | A | | B |
| | | | | |
+--------+ | DHCP PROXY PDS | | PROXY PDS |
+----------------------+ +----------------------+
| | | | | |
(A) |<====DHCP====>| | | | |
| | | | |
| | | | |
| Profile Enrollment | | | |
(B) |<local-network profile>|<====>| | |
|
| <<Profile content retrieval>>
|
|
| Profile Enrollment | | | |
(C) |<== device profile ==> |<====>| | |
|
| <<Profile content retrieval>>
|
.
.
.
| Profile Enrollment | | | |
(D) |<= user profile (A) => |<====>| | |
| | | | |
|
| <<Profile content retrieval>>
.
[[User A obtains services]]
.
.
.
|
| Profile Enrollment | |
(E) |<=========== user profile (B) ==========>|<=========>|
| | |
| <<Profile content retrieval>>
|
[[User B obtains services]]
Figure 5: Use Case 2
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The following is an explanation of the interactions in Figure 5.
(A) Upon initialization, the device obtains IP configuration
parameters using DHCP. This also provides the local domain
information to help with local-network profile enrollment.
(B) The device requests profile enrollment for the local network
profile. It receives an enrollment notification containing
content indirection information from Provider A's PDS. The
device retrieves the profile (this contains useful information
such as firewall port restrictions and available bandwidth).
(C) The device then requests profile enrollment for the device
profile. It receives an enrollment notification resulting in
device profile content retrieval. The device initializes the
user interface for services.
(D) User A with a pre-existing service relationship with Provider A
attempts communication via the user interface. The device uses
the user supplied information (including any credential
information) and requests profile enrollment for user A's
profile. Successful enrollment and profile content retrieval
results in services for user A.
(E) At a different point in time, user B with a service relationship
with Provider B attempts communication via the user interface.
It enrolls and retrieves user B's profile and this results in
services for user B.
The discovery mechanisms for profile enrollment described by the
framework, or the profile data themselves, can result in outbound
proxies that support devices behind NATs, using procedures specified
in [RFC5626].
5. Profile Delivery Framework
This section specifies the profile delivery framework. It provides
the requirements for the three profile delivery stages introduced in
Section 3.4 and presents the associated security requirements. It
also presents considerations such as back-off and retry mechanisms.
5.1. Profile Delivery Stages
The three profile delivery stages -- enrollment, content retrieval,
and change notification -- apply separately to each profile type
specified for use with this framework. The following subsections
provide the requirements associated with each stage.
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5.1.1. Profile Enrollment
Profile enrollment is the process by means of which a device
requests, and receives, profile data. Each profile type specified in
this document requires an independent enrollment request. However, a
particular PDS can support enrollment for one or more profile types.
PDSs and devices MUST implement all of the three profile types. A
device that has not been configured otherwise SHOULD try to obtain
all the three profile types, in the order specified by this
framework. The exceptions are bootstrapping when it SHOULD request
the device profile type (see Section 5.3.1) or when it has been
explicitly configured with a different order via mechanisms such as
previously retrieved profile data or pre-configuration or manual
configuration.
Profile enrollment consists of the following operations, in the
specified order.
Enrollment request transmission
Profile enrollment is initiated when the device transmits a SIP
SUBSCRIBE request [RFC3265] for the 'ua-profile' event package,
specified in Section 6. The profile being requested is indicated
using the 'profile-type' parameter. The device MUST transmit the
SIP SUBSCRIBE message via configured outbound proxies for the
destination domain, or in accordance with RFC 3263 [RFC3263].
The device needs certain data to create an enrollment request,
form a Request-URI, and authenticate to the network. This
includes the profile provider's domain name and device or user
identities and credentials. Such data can be "configured" during
device manufacturing, by the user, or via profile data enrollment
(see Section 5.3.1). The data can also be "discovered" using the
procedures specified by this framework. The "discovered" data can
be retained across device resets (but not across factory resets)
and such data is referred to as "cached". Thus, data can be
configured, discovered, or cached. The following requirements
apply.
* If the device is configured with a specific domain name (for
the local network provider or device provider), it MUST NOT
attempt "discovery" of the domain name. This is the case when
the device is pre-configured (e.g., via a user interface) to be
managed by specific entities.
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* The device MUST only use data associated with the provider's
domain in an enrollment request. As an example, when the
device is requesting a local-network profile in the domain
'example.net', it cannot present a user Address of Record (AoR)
associated with the local domain 'example.com'.
* The device SHOULD adhere to the following order of data usage:
configured, cached, and discovered. An exception is when the
device is explicitly configured to use a different order.
Upon failure to obtain the profile using any methods specified in
this framework, the device MAY provide a user interface to allow
for user intervention. This can result in temporary, one-time
data to bootstrap the device. Such temporary data is not
considered to be "configured" and SHOULD NOT be cached across
resets. The configuration obtained using such data MAY provide
the configuration data required for the device to continue
functioning normally.
Devices attempting enrollment MUST comply with the SIP-specific
event notification specified in [RFC3265], the event package
requirements specified in Section 6.2, and the security
requirements specified in Section 5.2.
Enrollment request admittance
A PDS or a SIP proxy will receive a transmitted enrollment
request. If a SIP infrastructure element receives the request, it
will relay it to the authoritative proxy for the domain indicated
in the Request-URI (the same way it would handle any other
SUBSCRIBE message). The authoritative proxy is required to
examine the request (e.g., event package) and transmit it to a PDS
capable of addressing the profile enrollment request.
A PDS receiving the enrollment request SHOULD respond to the
request, or proxy it to a PDS that can respond. An exception to
responding or proxying the request is when a policy prevents
response (e.g., recognition of a denial-of-service (DoS) attack,
an invalid device, etc.). The PDS then verifies the identity
presented in the request and performs any necessary
authentication. Once authentication is successful, the PDS MUST
either admit or reject the enrollment request, based on applicable
authorization policies. A PDS admitting the enrollment request
indicates it via a 2xx-class response, as specified in [RFC3265].
Refer to Sections 6.6 and 5.2 for more information on subscription
request handling and security requirements, respectively.
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Enrollment request acceptance
A PDS that admits the enrollment request verifies applicable
policies, identifies the requested profile data and prepares a SIP
NOTIFY message to the device. Such a notification can either
contain the profile data or contain content indirection
information that results in the device performing profile content
retrieval. The PDS then transmits the prepared SIP notification.
When the device successfully receives and accepts the SIP
notification, profile enrollment is complete.
When it receives the SIP NOTIFY message, indicating successful
profile enrollment, the device SHOULD make the new profile
effective within the specified time frame, as described in
Section 6.2. The exception is when the profile data is delivered
via content indirection, and the device cannot obtain the profile
data within the specified time frame.
Once profile enrollment is successful, the PDS MUST consider the
device enrolled for the specific profile, for the duration of the
subscription.
5.1.2. Content Retrieval
A successful profile enrollment leads to an initial SIP notification,
and may result in subsequent change notifications. Each of these
notifications can either contain profile data or content indirection
information. If it contains content indirection information, the
device is required to retrieve the profile data using the specified
content retrieval protocols. This process is termed "profile content
retrieval". For information regarding the use of the SIP NOTIFY
message body, please refer to Section 6.5.
Devices and PDSs implementing this framework MUST implement two
content retrieval protocols: HTTP and HTTPS, as specified in
[RFC2616] and [RFC2818], respectively. Future enhancements or usage
of this framework may specify additional or alternative content
retrieval protocols. For security requirements and considerations,
please refer to Section 5.2.
5.1.3. Change Notification
Profile data can change over time. Changes can be initiated by
various entities (e.g., via the device, back-office components, and
end-user web interfaces) and for various reasons (e.g., change in
user preferences and modifications to services). Profiles may also
be shared by multiple devices simultaneously. When a profile is
changed, the PDS MUST inform all the devices currently enrolled for
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the specific profile. This process of informing a device of any
changes to the profile that it is currently enrolled for is termed
change notification.
The PDS provides change notification using a SIP notification (the
SIP NOTIFY message, as specified in [RFC3265]). The SIP notification
may provide the changes, a revised profile, or content indirection,
which contains a pointer to the revised data. When a device
successfully receives a profile change notification for an enrolled
profile, it MUST act upon the changes prior to the expiration of the
'effective-by' parameter.
For NOTIFY content, please refer to Section 6.5.
5.1.4. Enrollment Data and Caching
The requirements for the contents of the SIP SUBSCRIBE used to
request profile enrollment are described in this section. The data
required can be configured, cached, or discovered -- depending on the
profile type. If the data is not configured, the device MUST use
relevant cached data or proceed with data discovery. This section
describes the requirements for creating a SIP SUBSCRIBE for
enrollment, the caching requirements and how data can be discovered.
5.1.4.1. Local-Network Profile
To create a Subscription URI to request the local-network profile, a
device needs the local network domain name, the device identifier,
and optionally a user AoR with associated credentials (if one is
configured). Since the device can be potentially initialized in a
different local network each time, it SHOULD NOT cache the local
network domain, the SIP Subscription URI or the local-network profile
data across resets. An exception to this is when the device can
confirm that it is reinitialized in the same network (using means
outside the scope of this document). Thus, in most cases, the device
needs to discover the local network domain name. The device
discovers this by establishing IP connectivity in the local network
(such as via DHCP or pre-configured IP information). Once
established, the device MUST attempt to use the local network domain
obtained via pre-configuration, if available. If it is not pre-
configured, it MUST employ dynamic discovery using DHCPv4 ([RFC2132],
Domain Name option) or DHCPv6 ([RFC4704]). Once the local network
domain is obtained, the device creates the SIP SUBSCRIBE for
enrollment as described below.
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o The device MUST NOT populate the user part of the Request-URI.
The device MUST set the host portion of the Request-URI to the
dot-separated concatenation of "_sipuaconfig" and the local
network domain (see example below).
o If the device has been configured with a user AoR for the local
network domain (verified as explained in Section 5.2) the device
MUST use it to populate the From field, unless configured not to
(due to privacy concerns, for example). Otherwise, the device
MUST set the From field to a value of
"anonymous@anonymous.invalid".
o The device MUST include the +sip.instance parameter within the
Contact header, as specified in [RFC5626]. The device MUST ensure
that the value of this parameter is the same as that included in
any subsequent profile enrollment request.
For example, if the device requested and received the local domain
name via DHCP to be: airport.example.net, then the local-network
profile SUBSCRIBE Request-URI would look like:
sip:_sipuaconfig.airport.example.net
The local-network profile SUBSCRIBE Request-URI does not have a user
part so that the URI is distinct between the "local" and "device"
URIs when the domain is the same for the two. This provides a means
of routing to the appropriate PDS in domains where there are distinct
servers.
The From field is populated with the user AoR, if available. This
allows the local network provider to propagate user-specific profile
data, if available. The "+sip.instance" parameter within the Contact
header is set to the device identifier or specifically, the SIP UA
instance. Even though every device may get the same (or similar)
local-network profile, the uniqueness of the "+sip.instance"
parameter provides an important capability. Having unique instance
ID fields allows the management of the local network to track devices
present in the network and consequently also manage resources such as
bandwidth allocation.
5.1.4.2. Device Profile Type
Once associated with a device, the device provider is not expected to
change frequently. Thus, the device is allowed to, and SHOULD, cache
the Subscription URI for the device profile upon successful
enrollment. Exceptions include cases where the device identifier has
changed (e.g., new network card), device provider information has
changed (e.g., user initiated change), or the device cannot obtain
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its profile using the Subscription URI. Thus, when available, the
device MUST use a cached Subscription URI. If no cached URI is
available then it needs to create a Subscription URI. To create a
Subscription URI, the device needs a device identity and the device
provider's domain name. Unless already configured, the device needs
to discover the necessary information and form the Subscription URI.
In such cases, the following requirements apply for creating a
Subscription URI for requesting the device profile:
o The device MUST populate the user part of the Request-URI with the
device identifier. The device MUST set the host portion of the
Request-URI to the domain name of the device provider. The device
identifier format is explained in detail later in this section.
o The device MUST set the From field to a value of anonymous@<device
provider's domain>.
o The device MUST include the "+sip.instance" parameter within the
Contact header, as specified in [RFC5626]. The device MUST use
the same value as the one presented while requesting the local-
network profile.
Note that the discovered AoR for the Request-URI can be overridden by
a special, provisioned, AoR that is unique to the device. In such
cases, the provisioned AoR is used to form the Request-URI and to
populate the From field.
If the device is not configured with an AoR, and needs a domain name
to populate the Request-URI and the From field, it can either use a
configured domain name, if available, or discover it. The options to
discover are described below. The device MUST use the results of
each successful discovery process for one enrollment attempt, in the
order specified below.
o Option 1: Devices that support DHCP MUST attempt to obtain the
domain name of the outbound proxy during the DHCP process, using
the DHCP option for SIP servers defined in [RFC3361] or [RFC3319]
(for IPv4 and IPv6, respectively).
o Option 2: Devices that support DHCP MUST attempt to obtain the
local IP network domain during the DHCP process (refer to
[RFC2132] and [RFC4704]).
o Option 3: Devices MUST use the local network domain name
(configured or discovered to retrieve the local-network profile),
prefixing it with the label "_sipuaconfig".
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If the device needs to create a Subscription URI and needs to use its
device identifier, it MUST use the UUID-based (Universally Unique
Identifier) URN representation as specified in [RFC4122]. The
following requirements apply:
o When the device has a non-alterable Media Access Control (MAC)
address, it SHOULD use the version 1 UUID representation with the
timestamp and clock sequence bits set to a value of '0'. This
will allow for easy recognition, and uniqueness of MAC-address-
based UUIDs. An exception is the case where the device supports
independent device configuration for more than one SIP UA. An
example would be multiple SIP UAs on the same platform.
o If the device cannot use a non-alterable device identifier, it
SHOULD use an alternative non-alterable device identifier. For
example, the International Mobile Equipment Identity (IMEI) for
mobile devices.
o If the device cannot use a non-alterable MAC address, it MUST use
the same approach as defining a user agent instance ID in
[RFC5626].
o Note: when the URN is used as the user part of the Request-URI, it
MUST be URL escaped since the colon (":") is not a legal character
in the user part of an addr-spec ([RFC4122]), and must be escaped.
For example, the instance ID:
urn:uuid:f81d4fae-7ced-11d0-a765-00a0c91e6bf6@example.com
would be escaped to look as follows in a URI:
sip:urn%3auuid%3af81d4fae-7ced-11d0-a765-00a0c91e6bf6@
example.com
The ABNF ([RFC5234]) for the UUID representation is provided in
[RFC4122].
5.1.4.3. User Profile Type
To create a Subscription URI to request the user profile on behalf of
a user, the device needs to know the user's AoR. This can be
statically or dynamically configured on the device (e.g., user input,
or propagated as part of the device profile). Similar to device
profiles, the content and propagation of user profiles may differ,
based on deployment scenarios (i.e., users belonging to the same
domain may -- or may not -- be provided the same profile). To create
a Subscription URI, the following rules apply:
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o The device MUST set the Request-URI to the user AoR.
o The device MUST populate the From field with the user AoR.
An authoritative SIP proxy for a SIP provider's network that receives
a profile enrollment request for the user profile type will route
based on the Event Header field values, thus allowing a subscription
to the user's AoR to be routed to the appropriate PDS.
5.2. Securing Profile Delivery
Profile data can contain sensitive information that needs to be
secured, such as identities and credentials. Security involves
authentication, data integrity and data confidentiality.
Authentication is the process by which you verify that an entity is
who it claims to be, such as a user AoR presented during profile
enrollment. Message integrity provides the assurance that the
message contents transmitted between two entities, such as between
the PDS and the device, has not been modified during transit.
Privacy ensures that the message contents have not been subjected to
monitoring by unwanted elements during transit. Authentication and
data integrity are required to ensure that the profile contents were
received by a valid entity, from a valid source, and without any
modifications during transit. For profiles that contain sensitive
data, data confidentiality is also required.
For an overview of potential security threats, refer to Section 9.
For information on how the device can be configured with identities
and credentials, refer to Section 5.3.1. The following subsections
provide the security requirements associated with each profile
delivery stage, and applies to each of profile types specified by
this framework.
5.2.1. Securing Profile Enrollment
Profile enrollment may result in sensitive profile data. In such
cases, the PDS MUST authenticate the device, except during the
bootstrapping scenario when the device does not have existing
credentials (see Section 5.3.1 for more information on
bootstrapping). Additionally, the device MUST authenticate the PDS
to ensure that it is obtaining sensitive profile data from a valid
PDS.
To authenticate a device that has been configured with identities and
credentials, as specified in Section 5.3.1, and support profiles
containing sensitive profile data (refer to Section 5.3.3), devices
and PDSs MUST support digest authentication (over Transport Layer
Security (TLS)) as specified in [RFC3261]. Future enhancements may
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provide other authentication methods such as authentication using
X.509 certificates. For the device to authenticate the PDS, the
device MUST mutually authenticate with the PDS during digest
authentication (device challenges the PDS, which responds with the
Authorization header). Transmission of sensitive profile data also
requires data integrity. This can be accomplished by configuring the
device with, or by ensuring that the discovery process during profile
enrollment provides, a Session Initiation Protocol Secure (SIPS) URI
resulting in TLS establishment ([RFC5246]). TLS also prevents
offline dictionary attacks when digest authentication is used. Thus,
in the absence of TLS, the device MUST NOT respond to any
authentication challenges. It is to be noted that the digest
credentials used for obtaining profile data via this framework may,
or may not, be the same as those used for SIP registration (see
Section 5.3.1). In addition, while [RFC3261] considers MD5 to be a
reasonable choice to compute the hash, and this may have been true
when [RFC3261] was published, implementers are recommended to use
stronger alternatives such as SHA-256. Refer to [FIPS-180-3] and
[RFC4634] for more information about SHA-256.
When the PDS challenges a profile enrollment request, and it fails,
the PDS MAY refuse enrollment or provide profile data without the
user-specific information (e.g., to bootstrap a device as indicated
in Section 5.3.1). If the device challenges, but fails to
authenticate the PDS, it MUST reject the initial notification and
retry the profile enrollment process. If the device is configured
with, or discovers, a SIPS URI but TLS establishment fails because
the next-hop SIP entity does not support TLS, the device SHOULD
attempt other resolved next-hop SIP entities. When the device
establishes TLS with the next-hop entity, the device MUST use the
procedures specified in [RFC2818], Section 3.1, for authentication,
unless it does not have any configured information (e.g.,
certification authority (CA) certificate) to perform authentication
(like prior to bootstrapping). The 'Server Identity' for
authentication is always the domain of the next-hop SIP entity. If
the device attempts validation, and it fails, it MUST reject the
initial notification and retry profile enrollment. In the absence of
a SIPS URI for the device and a mechanism for mutual authentication,
the PDS MUST NOT present any sensitive profile data in the initial
notification, except when the device is being bootstrapped. It MAY
still use content indirection to transmit sensitive profile data.
When a device is being provided with bootstrapping profile data
within the notification, and it contains sensitive information, the
SIP Identity header SHOULD be used, as specified in [RFC4474]. This
helps with devices that MAY be pre-configured with certificates to
validate bootstrapping sources (e.g., list of allowed domain
certificates, or a list of root CA certificates using Public Key
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Infrastructure (PKI)). When the SIP Identity header is used, the PDS
MUST set the host portion of the AoR in the From header to the
Provider's domain (the user portion is a entity-specific identifier).
If the device is capable of validating the SIP Identity, and it
fails, it MUST reject bootstrapping profile data.
5.2.2. Securing Content Retrieval
Initial or change notifications following a successful enrollment can
provide a device with the requested profile data or use content
indirection to direct it to a PCC that can provide the profile data.
This document specifies HTTP and HTTPS as content retrieval
protocols.
If the profile is provided via content indirection and contains
sensitive profile data, then the PDS MUST use a HTTPS URI for content
indirection. PCCs and devices MUST NOT use HTTP for sensitive
profile data, except for bootstrapping a device via the device
profile. A device MUST authenticate the PCC as specified in
[RFC2818], Section 3.1. A device that is being provided with profile
data that contains sensitive data MUST be authenticated using digest
authentication as specified in [RFC2617], with the exception of a
device that is being bootstrapped for the first time via the device
profile. The resulting TLS channel also provides data integrity and
data confidentiality.
5.2.3. Securing Change Notification
If the device requested enrollment via a SIP subscription with a non-
zero 'Expires' parameter, it can also result in change notifications
for the duration of the subscription. For change notifications
containing sensitive profile data, this framework RECOMMENDS the use
of the SIP Identity header as specified in [RFC4474]. When the SIP
Identity header is used, the PDS MUST set the host portion of the AoR
in the From header to the Provider's domain (the user portion is a
entity-specific identifier). This provides header and body integrity
as well. However, for sensitive profile data requiring data
confidentiality , if the contact URI to which the NOTIFY request is
to be sent is not SIPS, the PDS MUST use content indirection.
Additionally, the PDS MUST also use content indirection for
notifications containing sensitive profile data, when the profile
enrollment was not authenticated.
5.3. Additional Considerations
This section provides additional considerations, such as details on
how a device obtains identities and credentials, back-off and retry
methods, guidelines on profile data, and additional profile types.
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5.3.1. Bootstrapping Identities and Credentials
When requesting a profile, the profile delivery server will likely
require the device to provide an identity (i.e., a user AoR) and
associated credentials for authentication. During this process
(e.g., digest authentication), the PDS is also required to present
its knowledge of the credentials to ensure mutual authentication (see
Section 5.2.1). For mutual authentication with the PDS, the device
needs to be provided with the necessary identities and credentials
(e.g., username/password, certificates). This is done via
bootstrapping. For a discussion around the security considerations
related to bootstrapping, please see Section 9.2.
Bootstrapping a device with the required identities and credentials
can be accomplished in one of the following ways:
Pre-configuration
The device may be pre-configured with identities and associated
credentials, such as a user AoR and digest password.
Out-of-band methods
A device or Provider may provide hardware- or software-based
credentials such as Subscriber Identity Module (SIM) cards or
Universal Serial Bus (USB) drives.
End-user interface
The end-user may be provided with the necessary identities and
credentials. The end-user can then configure the device (using a
user interface), or present when required (e.g., IM login screen).
Using this framework
When a device is initialized, even if it has no pre-configured
information, it can request the local-network and device profiles.
For purposes of bootstrapping, this framework recommends that the
device profile provide one of the following to bootstrap the
device:
* Profile data that allows the end-user to communicate with the
device provider or SIP service provider using non-SIP methods.
For example, the profile data can direct the end-user to a web
portal to obtain a subscription. Upon obtaining a successful
subscription, the end-user or the device can be provided with
the necessary identities and credentials.
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* Content indirection information to a PCC that can provide
identities and credentials. As an example, consider a device
that has an X.509 certificate that can be authenticated by the
PCC. In such a case, the PCC can use HTTPS to provide
identities and associated credentials.
* Profile data containing identities and credentials that can be
used to bootstrap the device (see Section 5.3.3 for profile
data recommendations). This can be used in cases where the
device is initialized for the first time, or after a factory
reset. This can be considered only in cases where the device
is initialized in the Provider's network, for obvious security
reasons.
For interoperability purposes, this framework requires PDSs and
devices to support the last option (above), which is to use this
framework. Specifically, the option of providing identities and
credentials via the profile data MUST be supported.
Additionally, AoRs are typically known by PDSs that serve the domain
indicated by the AoR. Thus, devices can only present the configured
AoRs in the respective domains. An exception is the use of federated
identities. This allows a device to use a user's AoR in multiple
domains. Further even within the same domain, the device's domain
proxy and the PDS may be in two different realms, and as such may be
associated with different credentials for digest authentication. In
such cases, multiple credentials may be configured, and associated
with the realms in which they are to be used. This framework
specifies only digest authentication for profile enrollment and the
device is not expected to contain any other credentials. For profile
retrieval using content indirection, the device will need to support
additional credentials such as X.509 certificates (for TLS). Future
enhancements can specify additional credential types for profile
enrollment and retrieval.
5.3.2. Profile Enrollment Request Attempt
A state diagram representing a device requesting any specific profile
defined by this framework is shown in Figure 6.
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RFC 6080 SIP Configuration Framework March 2011
+------------+
| Initialize |
+-----+------+
|
|
V
+-------------+
| Prepare |
+--------->| Enrollment |<------------------+
| | Request | |
| +------+------+ |
+------+------+ | |
| Failure | Enroll. Req. prepared |
+-->| Handling & | /Send Req |
| | Delay | | |
| +-------------+ V |
| ^ ^ +-------------+ |
| | | | Await | |
| | +--------+ Enrollment | |
| | Timeout, | acceptance | |
| | non-2xx/- +------+------+ |
| | | |
| Timeout 200 OK/- Enrollment
| /Terminate | Timeout/-
| Enrollment V |
| | +--------------+ |
| | | Enrollment | |
| +------------+ accepted | |
Retries Exceeded |(await NOTIFY)| |
/Retry Enrollment +---+------+---+ |
| | | |
| | | |
| NOTIFY w. Content Ind| | NOTIFY w. Profile |
| /Retrieve Profile | | /Accept Profile |
| +------------+ +------------+ |
| | | |
| V V |
| +------------+ +------------+ |
+-----+ Retrieving | Retrieved | Enrollment +---+
,->| Profile +--/Apply Profile-->| Successful |
/ | | |(monitoring)|<--.
Timeout +--+---------+ +--+----+----+ :
/Retry ; ^ | : ;
`------' | NOTIFY w. Cont.Ind | `-------'
+---/Retrieve Profile-----+ NOTIFY w. Profile
/Apply Profile
Figure 6: Device State Diagram
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As a reminder:
o The timeout for SIP messages is specified by [RFC3261]. In the
cases where this is not specified such as the timeout to wait for
the initial notification during profile enrollment, it is left to
device implementations or future protocol enhancements.
o The timeout for profile retrieval using content indirection will
be as specified by profile retrieval protocols employed. If none
exists, it is left to device implementations.
In addition, since profile enrollment is a process unique to this
framework, the device MUST follow the enrollment attempt along with
exponential back-off and retry mechanisms as indicated in Figure 7.
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Function for Profile Enrollment ()
Init Function: Iteration i=0
Loop 1: Attempt
Loop 2: For each SIP Subscription URI
Loop 3: For each next-hop SIP entity
- Prepare and transmit Enrollment Request
- Await Enrollment Acceptance and initial NOTIFY
+ If the profile enrollment is successful
= Exit this function()
+ If profile enrollment fails due to an explicit
failure or a timeout as specified in [RFC3261]
= Continue with the next-hop SIP entity (Loop 3)
End Loop: Loop 3
End Loop: Loop 2
(Note: If you are here, profile enrollment did not succeed)
+ Is any valid cached profile data available?
= If yes, use it and continue with Loop 1
+ If the enrollment request is for a non-mandatory profile
= Start profile enrollment for the next profile,
if applicable
- Delay for 2^i*(64*T1); -- this is exponential back-off
- increment i;
- If i>8, reset i=8;
End loop: Loop 1
End Function()
Figure 7: Profile Enrollment Attempt (Pseudo-Code)
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The pseudo-code above (Figure 7) allows for cached profiles to be
used. However, any cached local-network profile MUST NOT be used
unless the device can ensure that it is in the same local network
that provided the cached data. This framework does not provide any
procedures for local network recognition. Any cached device and user
profiles MUST only be used in domains with which they are associated.
For example, a cached device profile is used only when the associated
domain matches the current device provider's domain. If a PDS wants
to invalidate a profile it may do so by transmitting a NOTIFY with an
'empty profile', i.e., profile instance without any included data (if
supported by the profile data model; not to be confused with an empty
NOTIFY), or via an explicit profile data element that invalidates the
data. A device receiving such a NOTIFY MUST discard the applicable
profile (i.e., it cannot even store it in the cache). Additionally,
if a factory reset is available and performed on a device, it MUST
reset the device to its initial state prior to any configuration.
Specifically, the device MUST set the device back to the state when
it was originally distributed.
The order of profile enrollment is important. For the profiles
specified in this framework, the device MUST enroll in the following
default order: local network, device, and user. The pseudo-code
presented earlier (Figure 7) differentiates between 'mandatory' and
'non-mandatory' profiles. This distinction is left to profile data
definitions.
It is to be noted that this framework does not allow the devices to
inform the PDSs of profile retrieval errors such as invalid data.
Follow-on standardization activities are expected to address this
feature.
5.3.3. Profile Data
This framework does not specify the contents for any profile type.
Follow-on standardization activities are expected to address profile
contents. However, the framework provides the following requirements
and recommendations for profile data definitions:
o The device profile type SHOULD specify parameters to configure the
identities and credentials for use in scenarios such as
bootstrapping (see Section 5.3.1) and run-time modifications to
identities and credentials. This framework recommends the device
profile provide the identities and credentials due to a couple of
reasons. The local-network profile may not always be available,
and even if present, may not be controlled by the device provider
who controls device configuration to provide services. Further,
the device may not have any users configured prior to being
bootstrapped, resulting in an absence of user profile requests.
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However, this framework does not prevent other profile types from
providing identities and credentials to meet deployment needs.
For example, the user profile can contain identities and
credentials for communicating with specific applications.
o Each profile MUST clearly identify if it may contain any sensitive
data. Such profiles MUST also identify the data elements that are
considered sensitive, i.e., data that cannot be disclosed to
unauthorized parties. As an example, a device profile definition
may identify itself as containing sensitive data and indicate data
such as device credentials to be sensitive.
o When the device receives multiple profiles, the contents of each
profile type SHOULD only contain data relevant to the entity it
represents. As an example, consider a device that obtains all the
defined profiles. Information pertaining to the local network is
contained in the 'local-network' profile and not the 'user'
profile. This does not preclude relevant data about a different
entity from being included in a profile type, e.g., the 'device'
profile type may contain information about the users allowed to
access services via the device. A profile may also contain
starting information to obtain subsequent profiles.
o Data overlap SHOULD be avoided across profile types, unless
necessary. If data overlap is present, prioritization of the data
is left to data definitions. As an example, the device profile
may contain the list of codecs to be used by the device and the
user profile (for a user on the device) may contain the codecs
preferred by the user. Thus, the same data (usable codecs) is
present in two profiles. However, the data definitions may
indicate that, to function effectively, any codec chosen for
communication needs to be present in both the profiles.
5.3.4. Profile Data Frameworks
The framework specified in this document does not address profile
data representation, storage, or retrieval protocols. It assumes
that the PDS has a PCC based on existing or other Profile Data
Frameworks.
While this framework does not impose specific constraints on any such
framework, it does allow for the propagation of profile content to
the PDS (specifically the PCC). Thus, Profile Data Frameworks or
retrieval frameworks used in conjunction with this framework MAY
consider techniques for propagating incremental, atomic changes to
the PDS. One means for propagating changes to a PDS is XML
Configuration Access Protocol (XCAP) ([RFC4825]).
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5.3.5. Additional Profile Types
This document specifies three profile types: local-network, device,
and user. However, there may be use cases for additional profile
types. e.g., profile types for application specific profile data or
to provide enterprise-specific policies. Definition of such
additional profile types is not prohibited, but considered out of
scope for this document. Such profile definitions MUST specify the
order of retrieval with respect to all the other profiles such as the
local-network, device, and user profile types defined in this
document.
5.3.6. Deployment Considerations
The framework defined in this document was designed to address
various deployment considerations, some of which are highlighted
below.
Provider relationships:
o The local network provider and the SIP service provider can often
be different entities, with no administrative or business
relationship with each other.
o There may be multiple SIP service providers involved, one for each
service to which a user subscribes (telephony service, instant
messaging, etc.); this framework does not specify explicit
behavior in such a scenario, but it does not prohibit its usage
either.
o Each user accessing services via the same device may subscribe to
different sets of services, from different service providers.
User-device relationship:
o The relationship between devices and users can be many-to-many
(e.g., a particular device may allow for many users to obtain
subscription services through it, and individual users may have
access to multiple devices).
o Each user may have different preferences for use of services, and
presentation of those services in the device user interface.
o Each user may have different personal information applicable to
use of the device, either as related to particular services, or
independent of them.
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5.4. Support for NATs
PDSs that support devices behind NATs, and devices that can be behind
NATs can use procedures specified in [RFC5626]. The Outbound proxies
can be configured or discovered. Clients that support such behavior
MUST include the 'outbound' option-tag in a Supported header field
value, and add the "ob" parameter, as specified in [RFC5626], within
the SIP SUBSCRIBE for profile enrollment.
6. Event Package Definition
The framework specified in this document proposes and specifies a new
SIP event package, as allowed by [RFC3265]. The purpose is to allow
for devices to subscribe to specific profile types with PDSs and for
the PDSs to notify the devices with the profile data or content
indirection information.
The requirements specified in [RFC3265] apply to this package. The
following subsections specify the event package description and the
associated requirements. The framework requirements are defined in
Section 5.
6.1. Event Package Name
The name of this package is "ua-profile". This value appears in the
Event header field present in SUBSCRIBE and NOTIFY requests for this
package, as defined in [RFC3265].
6.2. Event Package Parameters
This package defines the following new parameters for the event
header:
"profile-type", "vendor", "model", "version", and "effective-by"
The following rules apply:
o All the new parameters, with the exception of the "effective-by"
parameter, MUST only be used in SUBSCRIBE requests and ignored if
they appear in NOTIFY requests.
o The "effective-by" parameter is for use in NOTIFY requests only
and MUST be ignored if it appears in SUBSCRIBE requests.
The semantics of these new parameters are specified in the following
subsections.
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6.2.1. "profile-type" Parameter
The "profile-type" parameter is used to indicate the token name of
the profile type the user agent wishes to obtain and to be notified
of subsequent changes. This document defines three logical types of
profiles and their token names. They are as follows:
local-network: specifying the "local-network" type profile indicates
the desire for profile data, and potentially, profile change
notifications specific to the local network.
device: specifying the "device" type profile(s) indicates the desire
for the profile data, and potentially, profile change notification
that is specific to the device or user agent.
user: specifying the "user" type profile indicates the desire for
the profile data, and potentially, profile change notification
specific to the user.
The profile type is identified in the Event header parameter:
"profile-type". A separate SUBSCRIBE dialog is used for each profile
type. Thus, the subscription dialog on which a NOTIFY arrives
implies which profile's data is contained in, or referred to, by the
NOTIFY message body. The Accept header of the SUBSCRIBE request MUST
include the MIME types for all profile content types for which the
subscribing user agent wishes to retrieve profiles, or receive change
notifications.
In the following syntax definition using ABNF, EQUAL and token are
defined in [RFC3261]. It is to be noted that additional profile
types may be defined in subsequent documents.
Profile-type = "profile-type" EQUAL profile-value
profile-value = profile-types / token
profile-types = "device" / "user" / "local-network"
The "device", "user", or "local-network" token in the profile-type
parameter may represent a class or set of profile properties.
Follow-on standards defining specific profile contents may find it
desirable to define additional tokens for the profile-type parameter.
Also, additional content types may be defined along with the profile
formats that can be used in the Accept header of the SUBSCRIBE to
filter or indicate what data sets of the profile are desired.
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6.2.2. "vendor", "model", and "version" Parameters
The "vendor", "model", and "version" parameter values are tokens
specified by the implementer of the user agent. These parameters
MUST be provided in the SUBSCRIBE request for all profile types. The
implementer SHOULD use their DNS domain name (e.g., example.com) as
the value of the "vendor" parameter so that it is known to be unique,
unless there is a good reason not to. Examples of exceptions
include: if the vendor does not have an assigned DNS domain name, if
they are using a different vendor's implementation, etc. These
parameters are useful to the PDS to affect the profiles provided. In
some scenarios, it is desirable to provide different profiles based
upon these parameters. For example, feature property X in a profile
may work differently on two versions of the same user agent. This
gives the PDS the ability to compensate for or take advantage of the
differences. In the following ABNF defining the syntax, EQUAL and
quoted-string are defined in [RFC3261].
Vendor = "vendor" EQUAL quoted-string
Model = "model" EQUAL quoted-string
Version = "version" EQUAL quoted-string
6.2.3. "effective-by" Parameter
The "effective-by" parameter in the Event header of the NOTIFY
request specifies the maximum number of seconds before the user agent
MUST attempt to make the new profile effective. The "effective-by"
parameter MAY be provided in the NOTIFY request for any of the
profile types. A value of 0 (zero) indicates that the subscribing
user agent MUST attempt to make the profiles effective immediately
(despite possible service interruptions). This gives the PDS the
power to control when the profile is effective. This may be
important to resolve an emergency problem or disable a user agent
immediately. If it is absent, the device SHOULD attempt to make the
profile data effective at the earliest possible opportunity that does
not disrupt any services being offered. The "effective-by" parameter
is ignored in all messages other than the NOTIFY request. In the
following ABNF, EQUAL and DIGIT are defined in [RFC3261].
Effective-By = "effective-by" EQUAL 1*DIGIT
6.2.4. Summary of Event Parameters
The following are example Event headers that may occur in SUBSCRIBE
requests. These examples are not intended to be complete SUBSCRIBE
requests.
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Event: ua-profile;profile-type=device;
vendor="vendor.example.com";model="Z100";version="1.2.3"
Event: ua-profile;profile-type=user;
vendor="premier.example.com";model="trs8000";version="5.5"
The following are example Event headers that may occur in NOTIFY
requests. These example headers are not intended to be complete
SUBSCRIBE requests.
Event: ua-profile;effective-by=0
Event: ua-profile;effective-by=3600
The following table shows the use of Event header parameters in
SUBSCRIBE requests for the three profile types:
profile-type || device | user | local-network
=============================================
vendor || m | m | m
model || m | m | m
version || m | m | m
effective-by || | |
m - MUST be provided
s - SHOULD be provided
o - OPTIONAL to be provided
Non-specified means that the parameter has no meaning and should be
ignored.
The following table shows the use of Event header parameters in
NOTIFY requests for the three profile types:
profile-type || device | user | local-network
=============================================
vendor || | |
model || | |
version || | |
effective-by || o | o | o
6.3. SUBSCRIBE Bodies
This package defines no use of the SUBSCRIBE request body. If
present, it SHOULD be ignored. Exceptions include future
enhancements to the framework that may specify a use for the
SUBSCRIBE request body.
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6.4. Subscription Duration
The duration of a subscription is specific to SIP deployments, and no
specific recommendation is made by this event package. If absent, a
value of 86400 seconds (24 hours; 1 day) is RECOMMENDED since the
presence (or absence) of a device subscription is not time critical
to the regular functioning of the PDS.
It is to be noted that a one-time fetch of a profile, without ongoing
subscription, can be accomplished by setting the 'Expires' parameter
to a value of Zero, as specified in [RFC3265].
6.5. NOTIFY Bodies
The framework specifying the event package allows for the NOTIFY body
to contain the profile data, or a pointer to the profile data using
content indirection. For profile data delivered via content
indirection, i.e., a pointer to a PCC, then the Content-ID MIME
header, as described in [RFC4483], MUST be used for each profile
document URI. At a minimum, the "http:" [RFC2616] and "https:"
[RFC2818] URI schemes MUST be supported; other URI schemes MAY be
supported based on the Profile Data Frameworks (examples include FTP
[RFC0959], Lightweight Directory Access Protocol (LDAP) [RFC4510],
and XCAP [RFC4825] ).
A non-empty NOTIFY body MUST include a MIME type specified in the
Accept header of the SUBSCRIBE. Further, if the Accept header of the
SUBSCRIBE included the MIME type message/external-body (indicating
support for content indirection) then the PDS MAY use content
indirection in the NOTIFY body for providing the profiles.
6.6. Notifier Processing of SUBSCRIBE Requests
A successful SUBSCRIBE request results in a NOTIFY with either
profile contents or a pointer to it (via content indirection). The
SUBSCRIBE SHOULD be either authenticated or transmitted over an
integrity protected SIP communications channel. Exceptions include
cases where the identity of the Subscriber is unknown and the
Notifier is configured to accept such requests.
The Notifier MAY also authenticate SUBSCRIBE messages even if the
NOTIFY is expected to only contain a pointer to profile data.
Securing data sent via content indirection is covered in Section 9.
If the profile type indicated in the "profile-type" Event header
parameter is unavailable or the Notifier is configured not to provide
it, the Notifier SHOULD return a 404 response to the SUBSCRIBE
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request. If the specific user or device is unknown, the Notifier MAY
accept the subscription, or else it may reject the subscription (with
a 403 response).
6.7. Notifier Generation of NOTIFY Requests
As specified in [RFC3265], the Notifier MUST always send a NOTIFY
request upon accepting a subscription. If the device or user is
unknown and the Notifier chooses to accept the subscription, the
Notifier MAY either respond with profile data (e.g., default profile
data) or provide no profile information (i.e., empty NOTIFY).
If the identity indicated in the SUBSCRIBE request (From header) is a
known identity and the requested profile information is available
(i.e., as specified in the "profile-type" parameter of the Event
header), the Notifier SHOULD send a NOTIFY with profile data.
Profile data MAY be sent as profile contents or via content
indirection (if the content indirection MIME type was included in the
Accept header). The Notifier MUST NOT use any scheme that was not
indicated in the "schemes" Contact header field.
The Notifier MAY specify when the new profiles must be made effective
by the Subscriber by specifying a maximum time in seconds (zero or
more) in the "effective-by" Event header parameter.
If the SUBSCRIBE was received over an integrity protected SIP
communications channel, the Notifier SHOULD send the NOTIFY over the
same channel.
6.8. Subscriber Processing of NOTIFY Requests
A Subscriber to this event package MUST adhere to the NOTIFY request
processing behavior specified in [RFC3265]. If the Notifier
indicated an effective time (using the "effective-by" Event header
parameter), the Subscriber SHOULD attempt to make the profiles
effective within the specified time. Exceptions include deployments
that prohibit such behavior in certain cases (e.g., emergency
sessions are in progress). When profile data cannot be applied
within the recommended time frame and this affects device behavior,
any actions to be taken SHOULD be defined by the profile data
definitions. By default, the Subscriber is RECOMMENDED to make the
profiles effective as soon as possible.
When accepting content indirection, the Subscriber MUST always
support "http:" or "https:" and be prepared to accept NOTIFY messages
with those URI schemes. If the Subscriber wishes to support
alternative URI schemes they MUST each be indicated in the "schemes"
Contact header field parameter as defined in [RFC4483]. The
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Subscriber MUST also be prepared to receive a NOTIFY request with no
body. The subscriber MUST NOT reject the NOTIFY request with no
body. The subscription dialog MUST NOT be terminated by a empty
NOTIFY, i.e., with no body.
6.9. Handling of Forked Requests
This event package allows the creation of only one dialog as a result
of an initial SUBSCRIBE request as described in Section 4.4.9 of
[RFC3265]. It does not support the creation of multiple
subscriptions using forked SUBSCRIBE requests.
6.10. Rate of Notifications
The rate of notifications for the profiles in this framework is
deployment specific, but expected to be infrequent. Hence, the event
package specification does not specify a throttling or minimum period
between NOTIFY requests.
6.11. State Agents
State agents are not applicable to this event package.
7. Examples
This section provides examples along with sample SIP message bodies
relevant to this framework. Both the examples are derived from the
use case illustrated in Section 4.1, specifically the request for the
device profile. The examples are informative only.
7.1. Example 1: Device Requesting Profile
This example illustrates the detailed message flows between the
device and the SIP service provider's network for requesting and
retrieving the profile (the flow uses the device profile as an
example).
The following are assumed for this example:
o Device is assumed to have established local network connectivity;
NAT and firewall considerations are assumed to have been addressed
by the SIP service provider.
o Examples are snapshots only and do not illustrate all the
interactions between the device and the service provider's network
(and none between the entities in the SIP service provider's
network).
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o All SIP communication with the SIP service provider happens via a
SIP proxy.
o HTTP over TLS is assumed to be the Content Retrieval method used
(any suitable alternative can be used as well).
The flow diagram and an explanation of the messages follow.
+----------------------+
+--------+ | SIP Service Provider |
| Device | | |
|(SIP UA)| | SIP PDS HTTP |
+--------+ | PROXY Server |
| |
+----------------------+
| | | |
| | | |
| SUBSCRIBE | | |
(SReq)|--------device profile--------->| | |
| |------>| |
| |200 OK | |
| 200 OK |<------| |
(SRes)|<-------------------------------| | |
| | | |
| | NOTIFY| |
| NOTIFY (Content Indirection)|<------| |
(NTFY)|<-------------------------------| | |
| 200 OK | | |
(NRes)|------------------------------->|200 OK | |
| |------>| |
| |
| |
| |
|<<<<<<<<<<<<< TLS establishment >>>>>>>>>>>>>|
| |
| HTTP Request |
(XReq)|---------------------------------------------->|
| |
| HTTP Response |
(XRes)|<----------------------------------------------|
| |
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(SReq)
the device transmits a request for the 'device' profile using the
SIP SUBSCRIBE utilizing the event package specified in this
framework.
* Note: Some of the header fields (e.g., SUBSCRIBE, Event, Via)
are continued on a separate line due to format constraints of
this document.
SUBSCRIBE sip:urn%3auuid%3a00000000-0000-1000-0000-00FF8D82EDCB
@example.com SIP/2.0
Event: ua-profile;profile-type=device;vendor="vendor.example.net";
model="Z100";version="1.2.3"
From: anonymous@example.com;tag=1234
To: sip:urn%3auuid%3a00000000-0000-1000-0000-00FF8D82EDCB@example.com
Call-ID: 3573853342923422@192.0.2.44
CSeq: 2131 SUBSCRIBE
Contact: sip:urn%3auuid%3a00000000-0000-1000-0000-00FF8D82EDCB
@192.168.1.44
;+sip.instance="<urn:uuid:00000000-0000-0000-0000-123456789AB0>"
;schemes="http,https"
Via: SIP/2.0/TCP 192.0.2.41;
branch=z9hG4bK6d6d35b6e2a203104d97211a3d18f57a
Accept: message/external-body, application/x-z100-device-profile
Content-Length: 0
(SRes) the SUBSCRIBE request is received by a SIP proxy in the
service provider's network, which transmits it to the PDS. The
PDS accepts the response and responds with a 200 OK.
* Note: The device and the SIP proxy may have established a
secure communications channel (e.g., TLS).
(NTFY) subsequently, the PDS transmits a SIP NOTIFY message
indicating the profile location.
* Note: Some of the fields (e.g., content-type) are continued on
a separate line due to format constraints of this document.
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NOTIFY sip:urn%3auuid%3a00000000-0000-1000-0000-00FF8D82EDCB
@192.168.1.44 SIP/2.0
Event: ua-profile;effective-by=3600
From: sip:urn%3auuid%3a00000000-0000-1000-0000-00FF8D82EDCB@example.com
;tag=abca
To: sip:urn%3auuid%3a00000000-0000-1000-0000-00FF8D82EDCB@example.com
;tag=1234
Call-ID: 3573853342923422@192.0.2.44
CSeq: 322 NOTIFY
Via: SIP/2.0/UDP 192.0.2.3;
branch=z9hG4bK1e3effada91dc37fd5a0c95cbf6767d0
MIME-Version: 1.0
Content-Type: message/external-body; access-type="URL";
expiration="Mon, 01 Jan 2010 09:00:00 UTC";
URL="http://example.com/z100-000000000000.html";
size=9999;
hash=10AB568E91245681AC1B
Content-Type: application/x-z100-device-profile
Content-ID: <39EHF78SA@example.com>
.
.
.
(NRes) Device accepts the NOTIFY message and responds with a 200 OK.
(XReq) once the necessary secure communications channel is
established, the device sends an HTTP request to the HTTP server
indicated in the NOTIFY.
(XRes) the HTTP server responds to the request via a HTTP response
containing the profile contents.
7.2. Example 2: Device Obtaining Change Notification
The following example illustrates the case where a user (X) is
simultaneously accessing services via two different devices (e.g.,
multimedia entities on a PC and PDA) and has access to a user
interface that allows for changes to the user profile.
The following are assumed for this example:
o The devices (A & B) obtain the necessary profiles from the same
SIP service provider.
o The SIP service provider also provides a user interface that
allows the user to change preferences that impact the user
profile.
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The flow diagram and an explanation of the messages follow.
o Note: The example only shows retrieval of user X's profile, but it
may request and retrieve other profiles (e.g., local-network,
device).
----- -----
|User |_________| UI* | * = User Interface
| X | | |
----- -----
/ \
/ \
/ \ +----------------------+
+--------+ +--------+ | SIP Service Provider |
| Device | | Device | | |
| A | | B | | SIP PDS HTTP |
+--------+ +--------+ | PROXY Server |
+----------------------+
| | | |
| | | |
(A-EX)|<=Enrolls for User X's profile=>|<=====>| |
| | | |
| |
(A-RX)|<===Retrieves User X's profile================>|
| |
| | | | |
| | Enrolls for | | |
| (B-EX)|<== User X's ==>|<=====>| |
| | profile | | |
| | | | |
| | |
| (B-RX)|<= Retrieves User X's profile=>|
| |
| | |
| (HPut)|---------------------->|
| | |
| (HRes)|<----------------------|
| |
| | | |
| | NOTIFY| |
| NOTIFY |<------| |
(A-NT)|<-------------------------------| | |
| 200 OK | | |
(A-RS)|------------------------------->|200 OK | |
| |------>| |
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| |
| | | NOTIFY| |
| | NOTIFY |<------| |
| (B-NT)|<---------------| | |
| | 200 OK | | |
| (B-RS)|--------------->|200 OK | |
| | |------>| |
| |
| |
(A-RX)|<===Retrieves User X's profile================>|
| |
| | |
| | |
| (B-RX)|<= Retrieves User X's profile=>|
| | |
(A-EX) Device A discovers, enrolls, and obtains notification
related to user X's profile.
(A-RX) Device A retrieves user X's profile.
(B-EX) Device B discovers, enrolls, and obtains notification
related to user X's profile.
(B-RX) Device B retrieves user X's profile.
(HPut) Changes affected by the user via the user interface are
uploaded to the HTTP server.
* Note: The Unique Identifier (UI) itself can act as a
device and subscribe to user X's profile. This is not
the case in the example shown.
(HRes) Changes are accepted by the HTTP server.
(A-NT) PDS transmits a NOTIFY message to device A indicating the
changed profile. A sample message is shown below:
* Note: Some of the fields (e.g., Via) are continued on a
separate line due to format constraints of this document.
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NOTIFY sip:userX@192.0.2.44 SIP/2.0
Event: ua-profile;effective-by=3600
From: sip:userX@sip.example.net;tag=abcd
To: sip:userX@sip.example.net.net;tag=1234
Call-ID: 3573853342923422@192.0.2.44
CSeq: 322 NOTIFY
Via: SIP/2.0/UDP 192.0.2.3;
branch=z9hG4bK1e3effada91dc37fd5a0c95cbf6767d1
MIME-Version: 1.0
Content-Type: message/external-body; access-type="URL";
expiration="Mon, 01 Jan 2010 09:00:00 UTC";
URL="http://www.example.com/user-x-profile.html";
size=9999;
hash=123456789AAABBBCCCDD
.
.
.
(A-RS) Device A accepts the NOTIFY and sends a 200 OK.
(B-NT) PDS transmits a NOTIFY message to device B indicating the
changed profile. A sample message is shown below:
* Note: Some of the fields (e.g., Via) are continued on a
separate line due to format constraints of this document.
NOTIFY sip:userX@192.0.2.43 SIP/2.0
Event: ua-profile;effective-by=3600
From: sip:userX@sip.example.net;tag=abce
To: sip:userX@sip.example.net.net;tag=1234
Call-ID: 3573853342923422@192.0.2.43
CSeq: 322 NOTIFY
Via: SIP/2.0/UDP 192.0.2.3;
branch=z9hG4bK1e3effada91dc37fd5a0c95cbf6767d2
MIME-Version: 1.0
Content-Type: message/external-body; access-type="URL";
expiration="Mon, 01 Jan 2010 09:00:00 UTC";
URL="http://www.example.com/user-x-profile.html";
size=9999;
hash=123456789AAABBBCCCDD
.
.
.
(B-RS) Device B accepts the NOTIFY and sends a 200 OK.
(A-RX) Device A retrieves the updated profile pertaining to user X.
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(B-RX) Device B retrieves the updated profile pertaining to user X.
8. IANA Considerations
IANA has registered a SIP event package, event header parameters, and
SIP configuration profile types as outlined in the following
subsections.
8.1. SIP Event Package
This specification registers a new event package as defined in
[RFC3265]. The registration is as follows:
Package Name: ua-profile
Package or Template-Package: This is a package
Published Document: RFC 6080
Persons to Contact: Daniel Petrie <dan.ietf@SIPez.com>,
Sumanth Channabasappa <sumanth@cablelabs.com>
New event header parameters: profile-type, vendor, model, version,
effective-by (The profile-type parameter has predefined values.
The new event header parameters do not.)
The following table illustrates the additions to the IANA SIP "Header
Field Parameters and Parameter Values" registry:
Predefined
Header Field Parameter Name Values Reference
---------------------------- --------------- ---------- ---------
Event profile-type Yes [RFC6080]
Event vendor No [RFC6080]
Event model No [RFC6080]
Event version No [RFC6080]
Event effective-by No [RFC6080]
8.2. Registry of SIP Configuration Profile Types
IANA has registered new SIP configuration profile types at
http://www.iana.org in the "SIP Configuration Profile Types"
registry.
The registration procedures are "Specification Required", as
explained in "Guidelines for Writing an IANA Considerations Section
in RFCs" ([RFC5226]).
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Registrations with the IANA MUST include the profile type, and a
published document that describes its purpose and usage.
As this document specifies three SIP configuration profile types, the
initial IANA registration contains the information shown in the table
below.
Profile Type Reference
-------------- ---------
local-network [RFC6080]
device [RFC6080]
user [RFC6080]
9. Security Considerations
The framework specified in this document specifies profile delivery
stages, an event package, and three profile types to enable profile
delivery. The profile delivery stages are enrollment, content
retrieval, and change notification. The event package helps with
enrollment and change notifications. Each profile type allows for
profile retrieval from a PDS belonging to a specific provider.
Enrollment allows a device to request, and if successful, enroll with
a PDS to obtain profile data. To transmit the request the device
relies on configured, cached, or discovered data. Such data includes
provider domain names, identities, and credentials. The device
either uses configured outbound proxies or discovers the next-hop
entity using [RFC3263] that can result in a SIP proxy or the PDS. It
then transmits the request. A SIP proxy receiving the request uses
the Request-URI and event header contents to route it to a PDS (via
other SIP proxies, if required).
When a PDS receives the enrollment request, it can either challenge
any contained identity or admit the enrollment. Authorization rules
then decide if the enrollment gets accepted. If accepted, the PDS
sends an initial notification that contains either the profile data,
or content indirection information. The profile data can contain
generic profile data (common across multiple devices) or information
specific to an entity (such as the device or a user). If specific to
an entity, it may contain sensitive information such as credentials.
Disclosure of sensitive data can lead to threats such as
impersonation attacks (establishing rogue sessions), theft of service
(if services are obtainable), and zombie attacks. It is important
for the device to ensure the authenticity of the PNC and the PCC
since impersonation of the SIP service provider can lead to DoS and
man-in-the-middle (MITM) attacks.
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Profile content retrieval allows a device to retrieve profile data
via content indirection from a PCC. This communication is
accomplished using one of many profile delivery protocols or
frameworks, such as HTTP or HTTPS as specified in this document.
However, since the profile data returned is subject to the same
considerations as that sent via profile notification, similar threats
exist. For example, DoS attacks (rogue devices bombard the PCC with
requests for a specific profile) and attempts to modify erroneous
data onto the PCC (since the location and format may be known).
Thus, for the delivery of any sensitive profile data, authentication
of the entity requesting profile data is required. It is also
important for the requesting entity to authenticate the profile
source via content indirection and ensure that the sensitive profile
data is protected via data integrity. For sensitive data that should
not be disclosed to unauthorized parties, data confidentiality is
also required.
The following subsections highlight the security considerations that
are specific to each profile type.
9.1. Local-Network Profile
A local network may or may not (e.g., home router) support local-
network profiles as specified in this framework. Even if supported,
the PDS may only be configured with a generic local-network profile
that is provided to every device that requests the local-network
profile. Such a PDS may not implement any authentication
requirements or TLS.
Alternatively, certain deployments may require the entities -- device
and the PDS -- to authenticate each other prior to successful profile
enrollment. Such networks may pre-configure user identities to the
devices and allow user-specific local-network profiles. In such
networks, the PDS will support digest authentication, and the devices
are configured with user identities and credentials as specified in
Section 5.3.1. If sensitive profile data is being transmitted, the
user identity is a SIPS URI that results in TLS with the next-hop
(which is authenticated), and digest authentication is used by the
PDS and the device.
This framework supports both use cases and any variations in between.
However, devices obtaining local-network profiles from an
unauthenticated PDS are cautioned against potential MITM or PDS
impersonation attacks. This framework requires that a device reject
sensitive data, such as credentials, from unauthenticated local-
network sources. It also prohibits devices from responding to
authentication challenges in the absence of TLS on all hops as a
result of using a SIPS URI. Responding to unauthenticated challenges
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allows for dictionary attacks that can reveal weak passwords. The
only exception to accepting such sensitive data without
authentication of the PDS is in the case of bootstrapping (see
Section 5.3.1). In the case of bootstrapping, the methods employed
need to be aware of potential security threats such as impersonation.
SIP Identity is useful for the device to validate notifications in
the absence of a secure channel such as TLS when a SIPS URI is used.
In such cases, the device can validate the SIP Identity header to
verify the source of the profile notification, and the source of the
profile data when content indirection is not used. However, the
presence of the header does not guarantee the validity of the data.
It verifies the source and confirms data integrity, but the data
obtained from an undesired source may still be invalid, e.g., invalid
outbound proxy information, resulting in DoS. Thus, devices
requesting the local-network profile from unknown networks need to be
prepared to discard information that prevent retrieval of other,
required, profiles.
9.2. Device Profile
Device profiles deal with device-specific configuration. They may be
provided to unknown devices that are attempting to obtaining profiles
for purposes such as trials, self-subscription (not to be confused
with [RFC3265]), and emergency services [PHONEBCP].
This framework allows the device profile to be used for bootstrapping
a device. Such bootstrapping profile data may contain enough
information to connect to a Provider. For example, it may enable the
device to communicate with a device provider, allowing for trial or
self-subscription services via visual or audio interfaces (e.g.,
interactive voice response), or customer service representatives.
The profile data may also allow the device a choice of device
providers and allow the end-user to choose one. The profile data may
also contain identities and credentials (temporary or long-term) that
can be used to obtain further profile data from the network. This
framework recommends the use of the SIP Identity header by the PDS.
However, to be able to validate the SIP Identity header, the device
needs to be pre-configured with the knowledge of allowable domains or
certificates for validation (e.g., using PKI). If not, the device
can still guarantee header and body integrity if the profile data
contains the domain certificate (but the data can still be invalid or
malicious). In such cases, devices supporting user interfaces may
obtain confirmation from the user trying to bootstrap the device
(confirming header and body integrity). However, when the SIP
Identity header is not present, or the device is not capable of
validating it, the bootstrapping data is unauthenticated and obtained
without any integrity protection. Such bootstrapping data, however,
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may contain only temporary credentials (SIPS URI and digest
credentials) that can be used to reconnect to the network to ensure
data integrity and data confidentiality prior to obtaining long-term
credentials. It is to be noted that such devices are at the mercy of
the network they request the device profile from. If they are
initialized in a rogue network, or get hijacked by a rogue PDS, the
end-user may be left without desired device operation or, worse,
unwanted operation. To mitigate such factors the device provider may
communicate temporary credentials (e.g., passwords that can be
entered via an interface) or permanent credentials (e.g., a USB
device) to the end-user for connectivity. If such methods are used,
those credentials MUST be quickly replaced by large-entropy
credentials, to minimize the impact of dictionary attacks. Future
enhancements to this framework may specify device capabilities that
allow for authentication without any provider-specific configuration
(e.g., X.509 certificates using PKI can allow for authentication by
any provider with access to the CA certificate). Alternatively, the
device may be pre-configured with credentials for use with content
indirection mechanisms. In such circumstances a PDS can use secure
content indirection mechanism, such as HTTPS, to provide the
bootstrapping data.
Once a device is associated with a device provider the device profile
is vital to device operation. This is because the device profile can
contain important operational information such as users that are to
be allowed access (white-list or black-list), user credentials (if
required) and other sensitive information. Thus, it is necessary to
ensure that any device profile containing sensitive information is
obtained via an authenticated source, with integrity protection, and
delivered to an authenticated device. For sensitive information such
as credentials, data confidentiality is also required. The framework
requires that devices obtain sensitive information only from
authenticated entities except while it is being bootstrapped. In
cases where data confidentiality needs to be mandated for
notifications, the device provider can configure the device with a
SIPS URI, to be used as the Subscription URI, during profile
enrollment. The framework also requires a PDS presenting sensitive
profile data to use digest authentication. This ensures that the
data is delivered to an authenticated entity. Authentication of
profile retrieval via content indirection for sensitive profiles is
via HTTPS utilizing HTTP digest.
9.3. User Profile
Devices can only request user profiles for users that are known by a
SIP service provider. PDSs are required to reject user profile
enrollment requests for any users that are unknown in the network.
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For known user AoRs that are allowed to retrieve profiles, the
security considerations are similar to that of the device profile
(except for bootstrapping).
10. Acknowledgements
The author appreciates all those who contributed and commented on the
many iterations of this document. Detailed comments were provided by
the following individuals: Jonathan Rosenberg, Henning Schulzrinne,
Cullen Jennings, Rohan Mahy, Rich Schaaf, Volker Hilt, Adam Roach,
Hisham Khartabil, Henry Sinnreich, Martin Dolly, John Elwell, Elliot
Eichen, Robert Liao, Dale Worley, Francois Audet, Roni Even, Jason
Fischl, Josh Littlefield, and Nhut Nguyen.
The final revisions of this document were a product of design team
discussions. The editor wishes to extend special appreciation to the
following design team members for their numerous reviews and specific
contributions to various sections: Josh Littlefield (Overview,
Section 6), Peter Blatherwick (Section 6), Cullen Jennings
(Security), Sam Ganesan (Section 6), and Mary Barnes (layout, Section
6).
The following design team members are thanked for numerous reviews
and general contributions: Martin Dolly, Jason Fischl, Alvin Jiang,
and Francois Audet.
The following SIPPING WG members are thanked for numerous reviews,
comments and recommendations: John Elwell, Donald Lukacs, Roni Even,
David Robbins, Shida Schubert, and Eugene Nechamkin. The editor
would also like to extend a special thanks to the comments and
recommendations provided by the SIPPING WG, specifically Keith Drage
(restructuring proposal) and John Elwell (numerous reviews and
recommendations).
Additionally, appreciation is also due to Peter Koch for expert DNS
advice.
Finally, sincere appreciation is extended to the chairs (Mary Barnes
and Gonzalo Camarillo); the past/current Area Directors (Cullen
Jennings, Jon Peterson, and Robert Sparks) for facilitating
discussions, reviews, and contributions; and, the expert reviewers
from the IESG (Peter McCann, Catherine Meadows).
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11. References
11.1. Normative References
[FIPS-180-3] National Institute of Standards and Technology (NIST),
"Secure Hash Standard (SHS)", FIPS PUB 180-3,
October 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence,
S., Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access
Authentication", RFC 2617, June 1999.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G.,
Johnston, A., Peterson, J., Sparks, R., Handley, M.,
and E. Schooler, "SIP: Session Initiation Protocol",
RFC 3261, June 2002.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263,
June 2002.
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC3319] Schulzrinne, H. and B. Volz, "Dynamic Host
Configuration Protocol (DHCPv6) Options for Session
Initiation Protocol (SIP) Servers", RFC 3319,
July 2003.
[RFC3361] Schulzrinne, H., "Dynamic Host Configuration Protocol
(DHCP-for-IPv4) Option for Session Initiation Protocol
(SIP) Servers", RFC 3361, August 2002.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
July 2005.
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[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
Authenticated Identity Management in the Session
Initiation Protocol (SIP)", RFC 4474, August 2006.
[RFC4483] Burger, E., "A Mechanism for Content Indirection in
Session Initiation Protocol (SIP) Messages", RFC 4483,
May 2006.
[RFC4704] Volz, B., "The Dynamic Host Configuration Protocol for
IPv6 (DHCPv6) Client Fully Qualified Domain Name (FQDN)
Option", RFC 4704, October 2006.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008.
[RFC5626] Jennings, C., Mahy, R., and F. Audet, "Managing Client-
Initiated Connections in the Session Initiation
Protocol (SIP)", RFC 5626, October 2009.
11.2. Informative References
[PHONEBCP] Rosen, B. and J. Polk, "Best Current Practice for
Communications Services in support of Emergency
Calling", Work in Progress, October 2010.
[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP
Vendor Extensions", RFC 2132, March 1997.
[RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Technical Specification Road Map", RFC 4510,
June 2006.
[RFC4634] Eastlake, D. and T. Hansen, "US Secure Hash Algorithms
(SHA and HMAC-SHA)", RFC 4634, July 2006.
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[RFC4825] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)", RFC 4825,
May 2007.
Authors' Addresses
Daniel Petrie
SIPez LLC
246A Park Ave
Arlington, MA 02476
USA
EMail: dan.ietf@SIPez.com
URI: http://www.SIPez.com/
Sumanth Channabasappa (editor)
CableLabs
858 Coal Creek Circle
Louisville, CO 80027
USA
EMail: sumanth@cablelabs.com
URI: http://www.cablelabs.com/
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