SIPPING Working Group V. Hilt
Internet-Draft Bell Labs/Lucent Technologies
Expires: April 24, 2007 G. Camarillo
Ericsson
October 21, 2006
A Session Initiation Protocol (SIP) Event Package for Session-Specific
Session Policies.
draft-ietf-sipping-policy-package-02
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 24, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This specification defines a Session Initiation Protocol (SIP) event
package for session-specific policies. This event package enables
user agents to subscribe to session policies for a SIP session and to
receive notifications if these policies change.
Hilt & Camarillo Expires April 24, 2007 [Page 1]
Internet-Draft Session Policy Event Package October 2006
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Event Package Formal Definition . . . . . . . . . . . . . . . 4
3.1. Event Package Name . . . . . . . . . . . . . . . . . . . . 4
3.2. Event Package Parameters . . . . . . . . . . . . . . . . . 4
3.3. SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . . 4
3.4. Subscription Duration . . . . . . . . . . . . . . . . . . 5
3.5. NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . . 5
3.6. Subscriber generation of SUBSCRIBE requests . . . . . . . 6
3.7. Notifier processing of SUBSCRIBE requests . . . . . . . . 8
3.8. Notifier generation of NOTIFY requests . . . . . . . . . . 9
3.9. Subscriber processing of NOTIFY requests . . . . . . . . . 10
3.10. Handling of forked requests . . . . . . . . . . . . . . . 10
3.11. Rate of notifications . . . . . . . . . . . . . . . . . . 11
3.12. State Agents . . . . . . . . . . . . . . . . . . . . . . . 11
3.13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 11
4. Security Considerations . . . . . . . . . . . . . . . . . . . 14
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
5.1. Event Package Name . . . . . . . . . . . . . . . . . . . . 15
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 16
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Normative References . . . . . . . . . . . . . . . . . . . 16
6.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 18
Hilt & Camarillo Expires April 24, 2007 [Page 2]
Internet-Draft Session Policy Event Package October 2006
1. Introduction
The Framework for Session Initiation Protocol (SIP) [5] Session
Policies [7] specifies a protocol framework that enables a proxy to
define and impact policies on sessions such as the codecs or media
types to be used. This draft identifies two types of session
policies: session-specific and session-independent policies.
Session-specific policies are policies that are created for one
particular session, based on the session description of this session.
They enable a network intermediary to inspect the session description
a UA is proposing and to return a policy specifically generated for
this session description. For example, an intermediary could open
pinholes in a firewall/NAT for each media stream in a session and
return a policy that replaces the internal IP addresses and ports
with external ones. Since session-specific policies are tailored to
a session, they only apply to the session they are created for. A
user agent requests session-specific policies on a session-by-session
basis at the time a session is created and the session description is
known. Session-independent policies on the other hand are policies
that are created independent of a session and generally apply to all
the SIP sessions set up by a user agent (see [7]).
The Framework for SIP Session Policies [7] defines a mechanism that
enables UAs to discover the URIs of session-specific policy servers.
This specification defines a SIP event package [4] that enables UAs
to subscribe to session-specific policies on a policy server.
Subscribing to session-specific policies involves the following steps
(see [7]):
1. A user agent submits the details of the session it is trying to
establish to the policy server and asks whether a session using
these parameters is permissible. For example, a user agent might
propose a session that contains the media types audio and video.
2. The policy server generates a policy decision for this session
and returns the decision to the user agent. Possible policy
decisions are (1) to deny the session, (2) to propose changes to
the session parameters with which the session would be
acceptable, or (3) to accept the session as it was proposed. An
example for a policy decision is to disallow the use of video but
agree to all other aspects of the proposed session.
3. The policy server can update the policy decision at a later time.
A policy decision update can, for example, require additional
changes to the session (e.g. because the available bandwidth has
changed) or deny a previously accepted session (i.e. disallow the
continuation of a session).
The event package for session-specific policies enables a user agent
to subscribe to the policies for a SIP session following the above
Hilt & Camarillo Expires April 24, 2007 [Page 3]
Internet-Draft Session Policy Event Package October 2006
model. The subscriber initiates a subscription by submitting the
details of the session it is trying to establish to the notifier
(i.e. the policy server) in the body of a SUBSCRIBE request. The
notifier uses this information to determine the policy decision for
this session. It conveys the initial policy decision to the
subscriber in a NOTIFY and all changes to this decision in subsequent
NOTIFYs.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
3. Event Package Formal Definition
This document provides the details for defining a SIP event package
as required by RFC 3265 [4].
3.1. Event Package Name
The name of the event package defined in this specification is
"session-spec-policy".
3.2. Event Package Parameters
This package defines the optional event package parameter "local-
only". This parameter is only defined for NOTIFY requests and MUST
be ignored if received in a SUBSCRIBE request. The usage of the
"local-only" parameter is described in Section 3.3, Section 3.8 and
Section 3.9.
3.3. SUBSCRIBE Bodies
A SUBSCRIBE for this event package MUST contain a body that describes
a SIP session. The purpose of this body is to enable the notifier to
generate the policies the subscriber is interested in. In this event
package, the Request-URI, the event package name and event parameters
are not sufficient to determine the resource a subscription is for.
However, with the session description in the SUBSCRIBE body, the
notifier can generate the requested policy decision and create policy
events for this resource.
All subscribers and notifiers MUST support the MIME type
Hilt & Camarillo Expires April 24, 2007 [Page 4]
Internet-Draft Session Policy Event Package October 2006
"application/session-policy+xml" as defined in the User Agent Profile
Data Set for Media Policy [3]. The "application/session-policy+xml"
format is the default format for SUBSCRIBE bodies in this event
package. Subscribers and notifiers MAY negotiate the use of other
formats capable of representing a session.
Note: encoding the local and remote session description in the
Media Policy [3] format has a number of advantages compared to the
use of the SDP [9] format in SUBSCRIBE bodies: i) the Media Policy
format is more flexible and allows the inclusion of information
that can't be expressed in SDP (e.g. the target URI), ii) the
Media Policy format enables the encoding of local and remote
session descriptions in a single document (not requiring the use
of MIME multipart and new content disposition types), and iii) it
aligns the formats used for session-specific and session-
independent policies. A drawback is that it requires the UA to
generate encode SDP and session information in Media Policy
documents.
3.4. Subscription Duration
A subscription to the session-specific policy package is usually
established at the beginning of a session and terminated when the
corresponding session ends. A typical duration of a phone call is a
few minutes.
Since the duration of a subscription to the session-specific policy
package is related to the lifetime of the corresponding session, the
value for the duration of a subscription is largely irrelevant.
However, it SHOULD be longer than the typical duration of a session.
The default subscription duration for this event package is set to
two hours.
A subscription MAY be terminated before a session ends by the
notifier. For example, a notifier may terminate the subscription
after the initial policy notification has been sent to the subscriber
if it knows that these policies will not change during the session.
A subscriber MUST NOT terminate a subscription unless it is
terminating the session this subscription is for.
3.5. NOTIFY Bodies
In this event package, the body of a notification contains the
session policy requested by the subscriber. All subscribers and
notifiers MUST support the format "application/session-policy+xml"
[3] as a format for NOTIFY bodies.
The SUBSCRIBE request MAY contain an Accept header field. If no such
Hilt & Camarillo Expires April 24, 2007 [Page 5]
Internet-Draft Session Policy Event Package October 2006
header field is present, it has a default value of "application/
session-policy+xml". If the header field is present, it MUST include
"application/session-policy+xml", and MAY include any other MIME type
capable of representing session-specific policies. As defined RFC
3265 [4], the body of notifications MUST be in one of the formats
defined in the Accept header of the SUBSCRIBE request or in the
default format.
If the notifier uses the same format in NOTIFY bodies that was used
by the subscriber in the SUBSCRIBE body (e.g. "application/
session-policy+xml"), the notifier can expect that the subscriber
supports all format extensions that were used in the SUBSCRIBE body.
The notifier cannot assume that the subscriber supports other
extensions beyond that and SHOULD NOT use such extensions.
If the SUBSCRIBE request contained a representation of the local
session description and the subscription was accepted, then the
NOTIFY body MUST contain a policy for the local session description.
If the SUBSCRIBE request of an accepted subscription contained the
local and the remote session description, then the NOTIFY body MUST
contain two policies, one for the local and one for the remote
session description.
3.6. Subscriber generation of SUBSCRIBE requests
The subscriber follows the general rules for generating SUBSCRIBE
requests defined in [4]. The subscriber MUST include enough
information in the SUBSCRIBE body to accurately describe the session
for which it seeks to receive session-specific policies. It MUST use
the most recent session description if multiple versions are
available.
OPEN ISSUE: how much information should a UA disclose to the
policy server. In general, it seems desirable that the UA always
discloses all elements in the session description that can be
mapped to the media data set format and a few extra fields (e.g.
request URI, session ID). This may require guidelines for
building media policy data set the documents.
Subscriptions to this event package are typically created in
conjunction with an SDP offer/answer exchange [8] during the
establishment of a session (see [7]). If used with an offer/answer
exchange, the subscriber MUST insert the representation of the local
session description in the SUBSCRIBE body. The local session
description is the one that was created by the subscriber (e.g. the
offer if the subscriber has initiated the offer/answer exchange).
Under certain circumstances, a UA may not have a session description
when subscribing to session-specific policies, for example, when it
Hilt & Camarillo Expires April 24, 2007 [Page 6]
Internet-Draft Session Policy Event Package October 2006
is composing an empty INVITE request (i.e. an INVITE request that
does not contain an offer). In these cases, a UA SHOULD establish a
subscription without including a representation of the local session
description. The UA MUST send another SUBSCRIBE request that
contains this session description as soon as the session description
becomes available, for example, because the UA has received a 200 OK
to an empty INVITE request. A policy server can choose to admit a
session only after the UA has disclosed the session descriptions.
The subscriber SHOULD also include a representation of the remote
session description in the SUBSCRIBE body. The remote session
description is the one the subscriber has received (i.e. the answer
if the subscriber has initiated the offer/answer exchange). In some
scenarios, the remote session description is not available to the
subscriber at the time the subscription to session-specific policies
is established. In this case, the initial SUBSCRIBE message SHOULD
only contain a representation of the local session description. When
the remote description becomes available, the subscriber SHOULD
refresh the subscription by sending another SUBSCRIBE request, which
then contains the local and the remote session description, unless
the subscriber has received a NOTIFY with the "local-only" parameter.
This parameter indicates that the notifier does not need to see the
remote session description.
A user agent can change the session description of an ongoing
session. A change in the session description will typically affect
the policy decisions for this session. A subscriber MUST refresh the
subscription to session-specific policies every time the session
description of a session changes. It does so by sending a SUBSCRIBE
request, which contains the details of the updated session
descriptions.
A subscriber may receive a error that indicates a server failure in
response to a SUBSCRIBE request. In this case, the subscriber SHOULD
try to locate an alternative server, for example, using the
procedures described in [6]. If no alternative server can be
located, the subscriber MAY continue with the session for which it
wanted to receive session-specific policies without subscribing to
session-specific policies. This is to avoid that a failed policy
server prevents a UA from setting up or continuing with a session.
Since the sessions created by the UA may not be policy compliant
without this subscription, they may be blocked by policy enforcement
mechanisms if they are in place.
Session policies can contain sensitive information. Moreover, policy
decisions can significantly impact the behavior of a user agent. A
user agent should therefore verify the identity of a policy server
and make sure that policies have not been altered in transit. All
Hilt & Camarillo Expires April 24, 2007 [Page 7]
Internet-Draft Session Policy Event Package October 2006
implementations of this package MUST support TLS [2] and the SIPS URI
scheme. A subscriber SHOULD use SIPS URIs when subscribing to
session-specific policies so that policies are transmitted over TLS.
See Section 4.
3.7. Notifier processing of SUBSCRIBE requests
All subscriptions to session-specific policies SHOULD be
authenticated and authorized before approval. The notifier SHOULD
authenticate the subscriber using any of the techniques available
through SIP, including digest, S/MIME, TLS or other transport
specific mechanisms. Administrators SHOULD use a SIPS URI as a
policy server URI. See Section 4.
The authorization policy is at the discretion of the administrator.
In general, all users SHOULD be allowed to subscribe to the session-
specific policies of their sessions. A subscription to this event
package will typically be established by a device that needs to know
about the policies for its sessions. However, subscriptions may also
be established by applications (e.g. a conference server). In those
cases, an authorization policy will typically be provided for these
applications.
Responding in a timely manner to a SUBSCRIBE request is crucial for
this event package. A notifier must minimize the time needed for
processing SUBSCRIBE requests and generating the initial NOTIFY.
This includes minimizing the time needed to generate an initial
policy decision. A short response time is in particular important
for this event package since it minimizes the delay for fetching
policies during an INVITE transaction and therefore reduces call
setup time. In addition, subscriptions to session-specific policies
can be established while the subscriber is in an INVITE transaction
at a point where it has received the 200 OK but before sending the
ACK. Delaying the creation of the initial NOTIFY would delay the
transmission of the ACK. A more detailed discussion of this scenario
can be found in [7].
A subscriber may not have disclosed enough information in the
SUBSCRIBE request to enable the notifier to generate a policy
decision. For example, if a UA may have subscribed to session-
specific policies without including the representation of a session
description. The policy server SHOULD accept such a subscription.
However, it SHOULD generate a NOTIFY request within the subscription
that indicates that a policy decision could not be made due to
insufficient information. This can be expressed by either generating
a NOTIFY request with an empty body or by inserting a corresponding
policy decision document into the NOTIFY body.
Hilt & Camarillo Expires April 24, 2007 [Page 8]
Internet-Draft Session Policy Event Package October 2006
OPEN ISSUE: in the latter case, the policy document needs to be
able to express that the policy decision is still pending due to
insufficient information.
3.8. Notifier generation of NOTIFY requests
A notifier sends a notification in response to SUBSCRIBE requests as
defined in RFC 3265 [4]. In addition, a notifier MAY send a
notification at any time during the subscription. Typically, it will
send one every time the policy decision this subscription is for has
changed. When and why a policy decision changes is entirely at the
discretion of the administrator. A policy decision can change for
many reasons. For example, a network may become congested due to an
increase in traffic and reduces the bandwidth available to an
individual user. Another example is a session that has been started
during "business hours" and continues into "evening hours" where more
bandwidth or video sessions are available to the user according to
the service level agreement.
Policy decisions are expressed in the format negotiated for the
NOTIFY body (e.g. "application/session-policy+xml"). The policy
document in a NOTIFY body MUST represent a complete policy decision.
Notifications that contain the deltas to previous policy decisions or
partial policy decisions are not supported in this event package.
The notifier SHOULD terminate the subscription if the policy decision
is to reject a session and if it can be expected that this decision
will not change in the foreseeable future. The notifier SHOULD keep
the subscription alive, if it rejects a session but expects that the
session can be admitted at a later point in time. For example, if
the session was rejected due to a temporary shortage of resources and
the notifier expects that these resources will become available again
shortly it should keep the subscription alive. A session is admitted
by returning a policy decision document that requires some or no
changes to the session.
If the notifier has not received enough information to make a policy
decision from the subscriber (e.g. because it did not receive a
session description), it SHOULD NOT terminate the subscription since
it can be expected that the UA refreshes the subscription with a
SUBSCRIBE request that contains more information. It SHOULD generate
a NOTIFY request with an empty body or with a body that contains a
policy decision document indicating that the decision could not be
made.
Some session-specific policies do not require the disclosure of the
remote session description to the notifier. If a notifier determines
that this is the case after receiving a SUBSCRIBE request, it MAY
Hilt & Camarillo Expires April 24, 2007 [Page 9]
Internet-Draft Session Policy Event Package October 2006
include the "local-only" event parameter in NOTIFY requests.
3.9. Subscriber processing of NOTIFY requests
A subscriber MUST apply the policy decision received in a NOTIFY to
the session associated with this subscription. If the UA decides not
to apply the received policy decision, it MUST NOT set up the session
and MUST terminate the session if it is already in progress. If the
UA has a pending INVITE transaction for this session, it MUST cancel
or reject the INVITE request.
If the subscriber receives a NOTIFY indicating that the session has
been rejected, it MUST NOT attempt to establish this session. The
notifier may still keep up the subscription after rejecting a session
and may send an updated policy decision to the subscriber at a later
time. This is useful, for example, if the session was rejected due
to a temporary shortage of resources and the notifier expects that
this problem to be resolved shortly. In this case, the subscriber
SHOULD not terminate the subscription to session-specific policies.
If the notifier has terminated the subscription after rejecting the
session, the subscriber SHOULD NOT try to re-subscribe for the same
session.
The subscriber may receive a NOTIFY which indicates that the
SUBSCRIBER request did not contain enough information. The
subscriber SHOULD re-subscribe with more complete information as soon
as the missing information (e.g. the session description) is
available.
A subscriber may receive an update to a policy decision for a session
that is already established. The subscriber MUST apply the new
policy decision to this session. If a UA decides that it does not
want to apply the new policy decision, it MUST terminate the session.
An updated policy decision may require the UA generate a re-INVITE or
UPDATE request in this session if the session description has changed
or it may need to terminate this session. A policy update that
requires a UA to terminate a session can, for example, be triggered
by the users account running out of credit or the detection of an
emergency that requires the termination of non-emergency calls.
If the subscriber receives a NOTIFY that contains the "local-only"
event parameter, it SHOULD NOT include the remote session description
in subsequent SUBSCRIBE requests within this subscription.
3.10. Handling of forked requests
This event package allows the creation of only one dialog as a result
of an initial SUBSCRIBE request. The techniques to achieve this
Hilt & Camarillo Expires April 24, 2007 [Page 10]
Internet-Draft Session Policy Event Package October 2006
behavior are described in [4].
3.11. Rate of notifications
It is anticipated that the rate of policy changes will be very low.
In any case, notifications SHOULD NOT be generated at a rate of more
than once every five seconds.
3.12. State Agents
State agents play no role in this package.
3.13. Examples
The following message flow illustrates how a user agent (Alice's
phone) can subscribe to session-specific policies when establishing a
call (here to Bob's phone). The flow assumes that the user agent has
already received the policy server URI (e.g. through configuration or
as described in [7]) and it does not show messages for authentication
on a transport or SIP level.
These call flow examples are informative and not normative.
Implementers should consult the main text of this document for exact
protocol details.
Policy Server Alice Bob
| | |
|(1) SUBSCRIBE | |
|<------------------| |
|(2) 200 OK | |
|------------------>| |
|(3) NOTIFY | |
|------------------>| |
|(4) 200 OK | |
|<------------------| |
| |(5) INVITE |
| |------------------>|
| | |
| |(6) 200 OK |
| |<------------------|
| |(7) ACK |
| |------------------>|
|(8) SUBSCRIBE | |
|<------------------| |
|(9) 200 OK | |
|------------------>| |
|(10) NOTIFY | |
Hilt & Camarillo Expires April 24, 2007 [Page 11]
Internet-Draft Session Policy Event Package October 2006
|------------------>| |
|(11) 200 OK | |
|<------------------| |
| | |
Message Details
(1) SUBSCRIBE Alice -> Policy Server
SUBSCRIBE sips:policy@biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS pc.biloxi.example.com:5061
;branch=z9hG4bK74bf
Max-Forwards: 70
From: Alice <sips:alice@biloxi.example.com>;tag=8675309
To: PS <sips:policy@biloxi.example.com>
Call-ID: rt4353gs2egg@pc.biloxi.example.com
CSeq: 1 SUBSCRIBE
Contact: <sips:alice@pc.biloxi.example.com>
Expires: 7200
Event: session-spec-policy
Accept: application/session-policy+xml
Content-Type: application/session-policy+xml
Content-Length: ...
[Local session description (offer)]
(2) 200 OK Policy Server -> Alice
(3) NOTIFY Policy Server -> Alice
NOTIFY sips:alice@pc.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS srvr.biloxi.example.com:5061
;branch=z9hG4bK74br
Max-Forwards: 70
From: PS <sips:policy@biloxi.example.com>;tag=31451098
To: Alice <sips:alice@biloxi.example.com>;tag=8675309
Call-ID: rt4353gs2egg@pc.biloxi.example.com
CSeq: 1 NOTIFY
Event: session-spec-policy
Subscription-State: active;expires=7200
Content-Type: application/session-policy+xml
Content-Length: ...
[Policy for local session description (offer)]
Hilt & Camarillo Expires April 24, 2007 [Page 12]
Internet-Draft Session Policy Event Package October 2006
(4) 200 OK Alice -> Policy Server
(5) INVITE Alice -> Bob
(6) 200 OK Bob -> Alice
(7) ACK Alice -> Bob
(8) SUBSCRIBE Alice -> Policy Server
SUBSCRIBE sips:policy@biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS pc.biloxi.example.com:5061
;branch=z9hG4bKna998sl
Max-Forwards: 70
From: Alice <sips:alice@biloxi.example.com>;tag=8675309
To: PS <sips:policy@biloxi.example.com>;tag=31451098
Call-ID: rt4353gs2egg@pc.biloxi.example.com
CSeq: 2 SUBSCRIBE
Expires: 7200
Event: session-spec-policy
Accept: application/session-policy+xml
Content-Type: application/session-policy+xml
Content-Length: ...
[Local session description (offer)]
[Remote session description (answer)]
(9) 200 OK Policy Server -> Alice
(10) NOTIFY Policy Server -> Alice
NOTIFY sips:alice@pc.biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS srvr.biloxi.example.com:5061
;branch=z9hG4bKna998sk
Max-Forwards: 70
From: PS <sips:policy@biloxi.example.com>;tag=31451098
To: Alice <sips:alice@biloxi.example.com>;tag=8675309
Call-ID: rt4353gs2egg@pc.biloxi.example.com
CSeq: 2 NOTIFY
Event: session-spec-policy
Subscription-State: active;expires=7200
Content-Type: application/session-policy+xml
Content-Length: ...
[Policy for local session description (offer)]
[Policy for remote session description (answer)]
Hilt & Camarillo Expires April 24, 2007 [Page 13]
Internet-Draft Session Policy Event Package October 2006
F6 200 OK Alice -> Policy Server
4. Security Considerations
Session policies can significantly change the behavior of a user
agent and can therefore be used by an attacker to compromise a user
agent. For example, session policies can be used to prevent a user
agent from successfully establishing a session (e.g. by setting the
available bandwidth to zero). Such a policy can be submitted to the
user agent during a session, which will cause the UA to terminate the
session.
A user agent transmits session information to a policy server. This
session information may contain sensitive data the user may not want
an eavesdropper or an unauthorized policy server to see. In
particular, the session information may contain the encryption keys
for media streams. Vice versa, session policies may also contain
sensitive information about the network or service level agreements
the service provider may not want to disclose to an eavesdropper or
an unauthorized user agent.
It is therefore important to secure the communication between the
user agent and the policy server. The following three discrete
attributes need to be protected:
1. mutual authentication between the user agent and the policy
server,
2. confidentiality of the messages exchanged between the user agent
and the policy server and
3. ensuring that private information is not exchanged between the
two parties, even over an confidentiality-assured and
authenticated session.
The confidentiality of the messages exchanged between the two parties
can be protected by encrypting the data stream through a TLS session
using the cipher suites specified in [5].
Accordingly, policy servers SHOULD be addressable only through a SIPS
URI and it MUST support TLS. In order to send a subscription to the
policy server, the user agent MUST support TLS, although it does not
need to possess a certificate. In such a case, the policy server
SHOULD authenticate the UA using HTTP Digest. The confidentiality of
the communication between the policy server and the user agent will
be assured as long as the policy server supports TLS and is reached
through a SIPS URI.
Hilt & Camarillo Expires April 24, 2007 [Page 14]
Internet-Draft Session Policy Event Package October 2006
Authenticating the two parties can performed using X.509 certificates
exchanged through TLS and other techniques such as HTTP Digest. When
the user agent establishes a TLS session with the policy server, the
policy server will present it a X.509 certificate. The user agent
SHOULD ensure that the identity of the policy server encoded in the
certificate matches the URI that the user received when it used the
Framework for SIP Session Policies [7] to retrieve a URI of a
session-specific policy server.
Likewise, when a policy server receives a new subscription (as
opposed to a refresh subscription), it should authenticate the user
agent using any means at its disposal. If the user agent has a TLS
certificate, the identity of the user agent SHOULD be contained in
the certificate, or if the user agent does not possess a certificate,
the policy server SHOULD challenge the user agent using HTTP Digest.
And finally, the fact that the user agent and the policy server have
successfully authenticated each other and have established a secure
TLS session does not absolve either one from ensuring that they do
not communicate sensitive information. For example, a session
description may contain sensitive information -- session keys, for
example -- that the user agent may not want to share with the policy
server; and indeed, the policy server does not need such information
to effectively formulate a policy. Thus, the user agent should not
insert such sensitive information in a policy document that it sends
to the policy server. Likewise, the policy server may have
information that is sensitive and of no use to the user agent --
network service level agreements, or network statistics, for example.
Thus, the policy server should refrain from transmitting such
information to the user agent.
5. IANA Considerations
5.1. Event Package Name
This specification registers an event package, based on the
registration procedures defined in RFC 3265 [2]. The following is
the information required for such a registration:
Package Name: session-spec-policy
Package or Template-Package: This is a package.
Published Document: RFC XXXX (Note to RFC Editor: Please fill in XXXX
with the RFC number of this specification).
Person to Contact: Volker Hilt, volkerh@bell-labs.com.
Hilt & Camarillo Expires April 24, 2007 [Page 15]
Internet-Draft Session Policy Event Package October 2006
Appendix A. Acknowledgements
Many thanks to Jonathan Rosenberg for the many discussions and
suggestions for this draft, to Roni Even, Bob Penfield, Mary Barnes
and Shida Schubert for reviewing the draft and providing feedback and
to Vijay Gurbani for the comments and input to the security
considerations section.
6. References
6.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[3] Hilt, V., Camarillo, G., and J. Rosenberg, "A User Agent Profile
Data Set for Media Policy",
draft-ietf-sipping-media-policy-dataset-02 (work in progress),
October 2006.
[4] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[5] 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.
[6] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[7] Hilt, V., Camarillo, G., and J. Rosenberg, "A Framework for
Session Initiation Protocol (SIP) Session Policies",
draft-ietf-sip-session-policy-framework-00 (work in progress),
October 2006.
6.2. Informative References
[8] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[9] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
Hilt & Camarillo Expires April 24, 2007 [Page 16]
Internet-Draft Session Policy Event Package October 2006
Authors' Addresses
Volker Hilt
Bell Labs/Lucent Technologies
101 Crawfords Corner Rd
Holmdel, NJ 07733
USA
Email: volkerh@bell-labs.com
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
Hilt & Camarillo Expires April 24, 2007 [Page 17]
Internet-Draft Session Policy Event Package October 2006
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Hilt & Camarillo Expires April 24, 2007 [Page 18]
