One document matched: draft-ono-sipping-providers-policy-00.txt
SIPPING K. Ono
Internet-Draft NTT Corporation
Expires: January 7, 2005 July 9, 2004
Discussion on Service Providers' Policies with the Session Initiation
Protocol (SIP)
draft-ono-sipping-providers-policy-00
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Abstract
Some service providers who operate SIP proxy servers and registrars
need to be able to express various types of policies to their
customers, such as media policies and security policies. Discussion
needs to take place about the types of policies and how they will
have an impact on SIP User Agents (UA)s. This document presents an
overview of the types of policies that might be available, and how
the operations of policies might be executed to aid in advancing the
current discussions on session policies.
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Conventions used in this document
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 [1].
Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Examples of Service Providers' Policies . . . . . . . . . . . 3
3. Policy Operations . . . . . . . . . . . . . . . . . . . . . . 3
4. A Mechanism of Operation #1: UAs disclose information that
providers utilize to determine session-dependent policies. . . 4
5. A Mechanism of Operation #2: Providers instruct UA about
the policies . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. A Mechanism of Operation #3: UAs comply with or don't
comply with the policies . . . . . . . . . . . . . . . . . . . 5
7. A Mechanism of Operation #4: Providers verify that UAs
follow the directives in the policies. . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . 8
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1. Overview
Some service providers operate SIP [2] proxy servers and registrars
to provide services, such as Voice over IP services and PSTN gateway
services. Service providers sometimes place limits on which SIP UAs
can connect to its network. However, to allow for interoperability
among different SIP UA implementations and the provider's servers, it
is necessary to notify SIP UAs of these policies. This document
provides examples of a typical service provider's policies, including
some that have not yet been discussed in the SIPPING WG. It also
discusses possible operations for these policies that will have an
impact on the operation of SIP UAs so as to get a better
understanding of what session policies need to accomplish.
2. Examples of Service Providers' Policies
We can classify the examples of policies into two categories: media
policies and security policies. Session policy work [3] mainly
focuses on media policies, and the e2m work [4] mainly focuses on
security policies.
o Media Policies
* Codec restrictions
* Call admission control for bandwidth management
o Security Policies
* User authentication for proxy servers
* Information disclosure for dynamic firewall control
* Information disclosure for logging services
* Information disclosure for location-based routing
3. Policy Operations
There are four operations that need to take place for providers'
policies to be reflected on UAs, these are listed below.
Operation #1: UAs disclose information that providers utilize to
determine session-dependent policies.
Operation #2: Provider's proxy servers instruct the UA about the
policies.
Operation #3: UAs comply with or don't comply with the policies.
Operation #4: Providers verify that UAs follow the directives in the
policies.
Operation #1 is only required for session-dependent policies. If the
policies are statically determined, such as user-by-user basis or for
all users, operation #1 is not required. While the media policies
have the possibility of being session-dependent and
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session-independent, the security policies are always
session-independent.
So far in discussions on the mailing list and at the meetings, the
WGs have discussed only operations #1 and #2. Operations #3 and #4
are out of scope of the session policies discussion, because only
media proxy servers can execute operation #4. However, use cases
described in [4] include Operations #3 and #4, because some of these
use cases are done in signaling messages, where media proxy servers
are not involved. An example is user authentication using HTTP
digest authentication in SIP.
4. A Mechanism of Operation #1: UAs disclose information that providers
utilize to determine session-dependent policies.
This operation #1 is needed, if the media policies are dependent of
session.
There are two mechanism options for this operation, which are both UA
driven. Since it is desirable to have the same mechanism to be
consistent over the consecutive operations, option#2 which is
congruent with the preferred option in operation #2 for the media
policies is more desirable.
Option #1: in-band
* Discloses information in messages, such as INVITE/200 or
UPDATE/ 200.
* Requires security for end-to-middle, no matter where the
information is set; a header or a body.
Option #2: out-of-band
* Discloses information in messages, such as PUBLISH or
SUBSCRIBE/NOTIFY.
* Requires the correlation with the session.
* Requires new data definition that contains media attributes of
a UAC and the UAS.
* Requires end-to-end security.
5. A Mechanism of Operation #2: Providers instruct UA about the
policies
There are two mechanism options: proxy server driven and UA driven
mechanisms. Policy servers are assumed to be co-located with proxy
servers.
Since option # 1 has several problems, option #2 is generally
preferable. The media policies are changeable during a session. The
lack of capability of dynamic notification could be a fatal problem
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in option #1. Therefore, option #2 is preferable for the media
policies.
However, the problems do not come into play for certain use cases.
For example, the security policies are not changeable during a
session. Some use cases of the security policies are only applied
only to a request message, that is to a UAC. Whether to utilize
in-band or out-of-band as the preferred mechanism depends on the use
cases of the security policies.
Option #1: in-band
* Instructs the policies by proxy server driven.
* Requires a proxy server to return an error response or to add
something to a response in order to notify a UAC.
* Requires a proxy server to add something to a request in order
to notify the UAS.[OPEN ISSUE]
* Requires middle-to-end security to secure policy information.
* Lacks of a capability of dynamic notification during a session.
[OPEN ISSUE]
* Discloses policies to other providers. [OPEN ISSUE]
Option #2: out-of-band
* Instructs the policies by UA driven.
* Requires correlation with the session.
* Requires end-to-end security.
6. A Mechanism of Operation #3: UAs comply with or don't comply with
the policies
There are two mechanism options for this operation, which are both UA
driven. The media policies feedback on media streams between the
UAs. Therefore, for the media policies, this operation, of course,
is accomplished with out-of-band.
For the security policies, whether to utilize in-band or out-of-band
as a possible mechanism, depends on the use cases. For example, user
authentication, logging services, and location-based routing are best
done using in-band signaling messages, because information that
effect the policies is conveyed within the signaling itself. Dynamic
firewall control can be accomplished with either out-of-band or
in-band, because information that effect the policies is conveyed
separately.
Option #1: in-band
* Appropriate use cases that information that effect the policies
is conveyed within the signaling.
* Requires the end-to-middle security.
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Option #2: out-of-band
* Appropriate use cases that information that effect the policies
is conveyed separately.
7. A Mechanism of Operation #4: Providers verify that UAs follow the
directives in the policies.
Media policies need media proxy servers to verify that media streams
of the UAs follow the directives. In case of security policies, the
proxy servers can reject to transfer the signaling messages unless
the UAs follow the directives. This operation is accomplished with
in-band.
8. Security Considerations
This document does not introduce a new mechanism.
9. IANA Considerations
This document requires no additional considerations.
10. Acknowledgments
I would like to thank Gonzalo Camarillo, Volker Hilt, Cyrus Shaoul
and Shida Schubert.
11 References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[3] Rosenberg, J., "Requirements for Session Policy for the Session
Initiation Protocol (SIP)",
draft-ietf-sipping-session-policy-req-01 (work in progress),
February 2004.
[4] Ono, K. and S. Tachimoto, "Requirements for End-to-middle
security in the Session Initiation Protocol(SIP)",
draft-ietf-sipping-e2m-sec-reqs-03 (work in progress), July
2004.
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Author's Address
Kumiko Ono
Network Service Systems Laboratories
NTT Corporation
9-11, Midori-Cho 3-Chome
Musashino-shi, Tokyo 180-8585
Japan
EMail: ono.kumiko@lab.ntt.co.jp
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