Internet Engineering Task Force (IETF) J. van Elburg
Request for Comments: 7316 Detecon International Gmbh
Category: Informational K. Drage
ISSN: 2070-1721 Alcatel-Lucent
M. Ohsugi
S. Schubert
K. Arai
NTT
July 2014
The Session Initiation Protocol (SIP) P-Private-Network-Indication
Private Header (P-Header)
Abstract
This document specifies the SIP P-Private-Network-Indication P-header
used by the 3GPP. The P-Private-Network-Indication indicates that
the message is part of the message traffic of a private network and
identifies that private network. A private network indication allows
nodes to treat private network traffic according to a different set
of rules than the set applicable to public network traffic.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see 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/rfc7316.
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Copyright Notice
Copyright (c) 2014 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
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................3
1.1. Overview ...................................................3
1.2. Applicability ..............................................3
1.3. Background .................................................3
1.4. Business Communication .....................................3
1.5. Indication Types ...........................................4
2. Conventions .....................................................6
3. Definitions .....................................................6
3.1. Traffic ....................................................6
3.2. Public Network Traffic .....................................6
3.3. Private Network Traffic ....................................6
3.4. Break-In ...................................................6
3.5. Break-Out ..................................................6
3.6. Trust Domain ...............................................6
4. Application of Terminology ......................................7
5. Overview of Solution ...........................................10
6. Proxy Behavior .................................................11
6.1. P-Private-Network-Indication Generation ...................11
6.2. P-Private-Network-Indication Consumption ..................11
6.3. P-Private-Network-Indication Removal ......................11
6.4. P-Private-Network-Indication Verification .................11
7. P-Private-Network-Indication Header Field Definition ...........12
8. Security Considerations ........................................12
9. IANA Considerations ............................................13
10. Acknowledgments ...............................................13
11. References ....................................................13
11.1. Normative References .....................................13
11.2. Informative References ...................................14
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1. Introduction
1.1. Overview
ETSI TISPAN (Telecommunications and Internet converged Services and
Protocols for Advanced Networking) defined Next Generation Networks
(NGNs), which use the 3GPP IP Multimedia Subsystem (IMS), which, in
turn, uses SIP [RFC3261] as its main signaling protocol. For more
information on the IMS, a detailed description can be found in 3GPP
TS 23.228 [3GPP.23.228] and 3GPP TS 24.229 [3GPP.24.229]. 3GPP and
ETSI TISPAN have identified a set of requirements that can be met by
defining a new optional SIP header, according to the procedures in
RFC 5727 [RFC5727].
1.2. Applicability
The P-Private-Network-Indication header field is intended to be used
in controlled closed networks like 3GPP IMS and ETSI TISPAN NGNs.
The P-Private-Network-Indication header is not intended for the
general Internet environment and is probably not suitable for such an
environment.
For example, there are no mechanisms defined to prevent spoofing of
this header. So, if a network were to accept calls carrying this
header from the general Internet, an attacker would be able to inject
information into private networks.
1.3. Background
The P-Private-Network-Indication header field has been referred to in
3GPP IMS specifications and has already been used in some networks as
an indicator for a specific capability. The header field has already
been implemented in some vendors' equipment in some countries. RFC
5727 [RFC5727] prohibits the new proposal of P-header "unless
existing deployments or standards use the prefix already". The
P-Private-Network-Indication header field is already used by existing
deployments and 3GPP standards; therefore, this is exactly the case
where the P-header is allowed as an exception.
1.4. Business Communication
ETSI TISPAN has identified a framework, which was adopted by 3GPP as
[3GPP.22.519], for the support of business communication capabilities
by the NGN. In addition to the direct attachment of Next Generation
Corporate Network (NGCN) equipment, this includes the capability to
"host" functionality relating to an enterprise within the NGN itself.
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These hosting arrangements are:
a) virtual leased line, where NGCN sites are interconnected through
the NGN;
b) business trunking application, where the NGN hosts transit
capabilities between NGCN's; break-in capabilities, where the NGN
converts public network traffic to private network traffic for
delivery at a served NGCN; and break-out capabilities, where the
NGN converts private network traffic from a served NGCN to public
network traffic; and
c) hosted enterprise services, where an NGN hosts originating and/or
terminating business communication capabilities for business
communication users that are directly attached to an NGN.
ETSI TISPAN has requirements that can be met by the introduction of
an explicit indication for private network traffic.
The traffic generated or received by a public NGN on behalf of a
private network can be either:
1) public network traffic: traffic sent to or received from an NGN
for processing according to the rules for ordinary subscribers of
a public telecommunication network. This type of traffic is
known as public network traffic.
2) private network traffic: traffic sent to the NGN for processing
according to an agreed set of rules specific to an enterprise.
This type of traffic is known as private network traffic.
Private network traffic is normally exchanged within a single
enterprise, but private network traffic can also be exchanged
between two or more different enterprises, based on some prior
arrangements, if not precluded for regulatory reasons.
1.5. Indication Types
A private network indication as proposed by this document indicates
to the receiving network element (supporting this specification) that
this request is related to private network traffic as opposed to
public network traffic. This indication does not identify an end
user on a private network and is not for delivery to an end user on
the private network. It is an indication that special service
arrangements apply (if such service is configured based on private
network traffic) for an enterprise; therefore, it is an indication of
service on behalf of an enterprise, not an indication of service to a
private network's end user.
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In order to allow NGN IMS nodes to perform different processing, ETSI
TISPAN formulated the following requirements for NGN. The NGN shall:
a) distinguish public network traffic from private network traffic;
and
b) distinguish private network traffic belonging to one enterprise
from that belonging to another enterprise.
To summarize, a few example reasons for a public NGN to make the
distinction between the two types of traffic include:
1) Different regulations apply to two types of traffic, for example,
emergency calls may be handled differently depending on the type
of traffic.
2) Different charging regimes may apply.
3) Call recording for business reasons (e.g., quality control,
training, non-repudiation) might apply only to a specific type of
traffic.
4) Different levels of signaling and/or media transparency may apply
to the different types of traffic.
There are several reasons why there is a need for an explicit
indication in the signaling:
a) Caller and callee addresses cannot always be used to determine
whether a certain call is to be treated as private or public
network traffic.
b) Nodes spanning multiple networks often need to have different
behavior depending upon the type of traffic. When this is done
using implicit schemes, enterprise-specific logic must be
distributed across multiple nodes in multiple operators'
networks. That is clearly not a manageable architecture and
solution.
c) There may be cases where treating the call as a public network
call although both participants are from the same enterprise is
advantageous to the enterprise.
Based on the background provided, this document formulates
requirements for SIP to support an explicit private network
indication and defines a P-header, P-Private-Network-Indication, to
support those requirements.
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2. Conventions
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 BCP 14, RFC 2119
[RFC2119].
3. Definitions
3.1. Traffic
In the context of this document, the term "traffic" is understood as
all communication pertaining to and/or controlled by a SIP
transaction or dialog.
3.2. Public Network Traffic
Traffic sent to or received from a public telecommunication network
for processing according to the rules for ordinary subscribers of a
public telecommunication network.
3.3. Private Network Traffic
Traffic sent to or received from a public telecommunication network
for processing according to an agreed set of rules specific to an
enterprise or a community of closely related enterprises.
3.4. Break-In
Act of converting public network traffic to private network traffic.
The header defined in this specification will be added to indicate
the traffic is a private network traffic after conversion.
3.5. Break-Out
Act of converting private network traffic to public network traffic.
The header defined in this specification will be removed to indicate
the traffic is a public network traffic after conversion.
3.6. Trust Domain
The term "trust domain" in this document is taken from P-Asserted-
Identity [RFC3324]. A trust domain applies to the private network
indication. The rules for specifying such a trust domain are
specified in P-Asserted-Identity [RFC3324] and require the
specification of a Spec(T) as covered in Section 2.4 of [RFC3324].
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The same information is required to specify a Spec(T) for purposes of
P-Private-Network-Indication as for P-Asserted-Identity [RFC3324].
However, if a network is using P-Private-Network-Indication as well
as other header fields subject to Spec(T) (such as P-Asserted-
Identity), the Spec(T) for each header field will probably be
different from the others.
4. Application of Terminology
Figure 1 shows the interconnection of sites belonging to two private
networks using the public network. Traffic in the public network
relating to the interconnection of the two sites of enterprise 1 are
tagged as private network traffic relating to enterprise 1. In
certain cases, an enterprise can also choose to send traffic from one
enterprise site to another enterprise site as public network traffic
when this is beneficial to the enterprise. Traffic in the public
network relating to the interconnection of the two sites of
enterprise 2 are tagged as private network traffic relating to
enterprise 2. Enterprise 1 also generates traffic to public phones,
and this is public network traffic (untagged in the public network).
There may be circumstances where traffic in the public network
between two different private networks is tagged as private network
traffic using a pre-arranged domain name agreed by the two involved
enterprises. This is illustrated by the interconnection of the site
from enterprise 3 and the site from enterprise 4.
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RFC 7316 Private Network Indication July 2014
+------------------------------+
| private network |
+------------+ |<===========traffic==========>| +------------+
| enterprise | | (enterprise 1) | | enterprise |
| 1 +-----+------------------------------+-----+ 1 !
| site 1 | | | | site 2 |
+------------+ | +---+-----| |
| public | | | |
/--\ |<=========network========>| | +------------+
o /\ o | traffic | |
/ \----------+--------------------------+ |
+----+ | |
public | |
phone | |
| private network |
+------------+ |<===========traffic==========>| +------------+
| enterprise | | (enterprise 2) | | enterprise |
| 2 +-----+------------------------------+-----+ 2 !
| site 1 | | | | site 2 |
+------------+ | | +------------+
| |
| private network |
+------------+ |<===========traffic==========>| +------------+
| enterprise | | (pre-arranged domain name) | | enterprise |
| 3 +-----+------------------------------+-----+ 4 !
| site 1 | | | | site 1 |
+------------+ | | +------------+
| |
+------------------------------+
Figure 1: Two Private Networks
Figure 2 shows the interconnection of sites belonging to a private
network using the public network and supported in the public network
by a server providing a business trunking application. The business
trunking application provides routing capabilities for the enterprise
traffic and supports the identification of calls to and from public
network users and routing of break-in and break-out of that traffic.
(Note that the business trunking application may consist of a
concatenation of application logic provided to the originating
enterprise site and application logic that is provided to the
terminating enterprise site.) Traffic in the public network relating
to the interconnection of the two sites of enterprise 1 is tagged as
private network traffic relating to enterprise 1. The business
trunking application also routes traffic to public phones, and this
is public network traffic (untagged in the public network).
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+-------------------------------------------------+
| private network |
+------------+ |<===========traffic============>+------------+ |
| enterprise | | (enterprise 1) | | |
| 1 +-----+--------------------------------+ | |
| site 1 | | | business | |
+------------+ | +-----+ trunking | |
| public | | application| |
/--\ |<=========network========>| +--+ | |
o /\ o | traffic | | | | |
/ \----------+--------------------------+ | | | |
+----+ | | +------------+ |
public | | |
phone | | |
| private network | |
+------------+ |<===========traffic=========>| |
| enterprise | | (enterprise 1) | |
| 1 +-----+-----------------------------+ |
| site 2 | | |
+------------+ | |
| |
+-------------------------------------------------+
Figure 2: Private Network and Business Trunking
Figure 3 shows the interconnection of sites belonging to a private
network on a server providing a hosted enterprise service application
(also known as Centrex). The hosted enterprise service application
supports phones belonging to the enterprise and is also able to route
traffic to and from public network phones using break-in or break-out
functionality. Traffic in the public network relating to the
interconnection of the site of enterprise 1 and the hosted enterprise
service belonging to enterprise 1 is tagged as private network
traffic relating to enterprise 1. The hosted enterprise service
application also routes traffic to public phones, and this is public
network traffic (untagged in the public network). Traffic from the
enterprise phones would not normally be tagged, but it can be tagged
as private network traffic. (Note that the hosted enterprise service
logic may precede or succeed a business trunking application that
offers services on behalf of an enterprise site.)
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+-------------------------------------------------+
| private network |
+------------+ |<===========traffic============>+------------+ |
| enterprise | | (enterprise 1) | | |
| 1 +-----+--------------------------------+ hosted | |
| site 1 | | | enterprise | |
+------------+ | +-----+ service | |
| public | | enterprise | |
/--\ |<=========network========>| +--+ 1 | |
o /\ o | traffic | | | | |
/ \----------+--------------------------+ | | | |
+----+ | | +------------+ |
public | | |
phone | | |
| private network | |
/--\ |<===========traffic=========>| |
o /\ o | (enterprise 1) | |
/ \----------+-----------------------------+ |
+----+ | |
enterprise | |
phone | |
+-------------------------------------------------+
Figure 3: Hosted Service and Private Network
5. Overview of Solution
The mechanism proposed in this document relies on a new header field
called 'P-Private-Network-Indication' that contains a private network
identifier expressed as a domain name, for example:
P-Private-Network-Indication: example.com
A proxy server that handles a message MAY insert such a P-Private-
Network-Indication header field into the message based on
authentication of the source of a message, configuration, or local
policy. A proxy server MAY forward the message to other proxies in
the same administrative domain or proxies in a trusted domain to be
handled as private network traffic. A proxy that forwards a message
to a proxy server or user agent (UA) that it does not trust MUST
remove the P-Private-Network-Indication header field before
forwarding the message.
The private network identifier expressed as a domain name allows it
to be a globally unique identifier, associated with the originating
and/or terminating enterprise(s). Domain name is used, as it allows
reuse of a company-owned Internet domain name without requiring an
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additional private network identifier registry. When the enterprise
needs more than one identifier, it can freely add subdomains under
its own control.
The formal syntax for the P-Private-Network-Indication header is
presented in Section 7.
6. Proxy Behavior
6.1. P-Private-Network-Indication Generation
Proxies that are responsible for determining certain traffic to be
treated as private network traffic or contain a break-in function
that converts incoming public network traffic to private network
traffic MUST insert a P-Private-Network-Indication header field into
incoming or outgoing requests for a dialog or for a standalone
transaction. The value MUST be set to the private network identifier
corresponding to the enterprise(s) to which the traffic belongs.
6.2. P-Private-Network-Indication Consumption
Proxies that are responsible for applying different processing
behaviors to specific private network traffic MUST support this
extension. The P-Private-Network-Indication header field MUST NOT be
used by a proxy in case it is received in a request from an entity
that it does not trust; in such a case, it MUST be removed before the
request is forwarded.
6.3. P-Private-Network-Indication Removal
Proxies that are at the edge of the trust domain or contain a break-
out function that converts incoming private network traffic to public
network traffic MUST remove the P-Private-Network-Indication header
field before forwarding a request that contains such a header field.
6.4. P-Private-Network-Indication Verification
When proxies supporting this specification receive a P-Private-
Network-Indication header field in a SIP request from a trusted node,
proxies MUST check whether the received domain name in the request is
the same as the domain name associated with the provisioned domain
name. If the received domain name does not match, proxies MUST
remove the P-Private-Network-Indication header field.
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7. P-Private-Network-Indication Header Field Definition
This document defines the SIP P-Private-Network-Indication header
field. This header field can be added by a proxy to initial requests
for a dialog or standalone requests. The presence of the P-Private-
Network-Indication header field signifies to proxies that understand
the header field that the request is to be treated as private network
traffic. The P-Private-Network-Indication header field contains a
domain name value that allows the private network traffic to be
associated with an enterprise to which it belongs and allows proxies
that understand this header field to process the request according to
the local policy configured for a specific enterprise(s).
The Augmented Backus-Naur Form (ABNF) [RFC5234] syntax of the
P-Private-Network-Indication header field is described below:
P-Private-Network-Indication = "P-Private-Network-Indication" HCOLON
PNI-value *(SEMI PNI-param)
PNI-param = generic-param
PNI-value = hostname
EQUAL, HCOLON, SEMI, hostname, and generic-param are defined in RFC
3261 [RFC3261].
The following is an example of a P-Private-Network-Indication header
field:
P-Private-Network-Indication: example.com
8. Security Considerations
The private network indication defined in this document MUST only be
used in the traffic transported between network elements that are
mutually trusted. Traffic protection between network elements can be
achieved by using security protocols such as IP Encapsulating
Security Payload (ESP) [RFC4303] or SIP / Transport Layer Security
(SIP/TLS) or sometimes by physical protection of the network. In any
case, the environment where the private network indication will be
used needs to ensure the integrity and the confidentiality of the
contents of this header field.
A private network indication received from an untrusted node MUST NOT
be used, and the information MUST be removed from a request or
response before it is forwarded to entities in the trust domain.
Additionally, local policies may be in place that ensure that all
requests entering the trust domain for private network indication
from untrusted nodes with a private network indication will be
discarded.
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There is a security risk if a private network indication is allowed
to propagate out of the trust domain where it was generated. The
indication may reveal information about the identity of the caller,
i.e., the organization that he belongs to. That is sensitive
information. It also reveals to the outside world that there is a
set of rules that this call is subject to that is different then the
rules that apply to public traffic. That is sensitive information
too. To prevent such a breach from happening, proxies MUST NOT
insert the information when forwarding requests to a next hop located
outside the trust domain. When forwarding the request to a trusted
node, proxies MUST NOT insert the header field unless they have
sufficient knowledge that the route set includes another proxy in the
trust domain that understands this header field. However, how to
learn such knowledge is out of the scope of this document. Proxies
MUST remove the information when forwarding requests to untrusted
nodes or when the proxy does not have knowledge of any other proxy in
the route set that is able to understand this header field.
9. IANA Considerations
This document defines a new SIP header field: P-Private-Network-
Indication. This header field has been registered by the IANA in the
"SIP Parameters" registry under the "Header Fields" subregistry.
RFC Number: [RFC7316]
Header Field Name: P-Private-Network-Indication
Compact Form: none
10. Acknowledgments
The authors would like to thank Richard Barnes, Mary Barnes, Atle
Monrad, Bruno Chatras, John Elwell, and Salvatore Loreto for
providing comments on an early version of this document. Further, we
thank John Elwell for performing the expert review.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
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[RFC3324] Watson, M., "Short Term Requirements for Network Asserted
Identity", RFC 3324, November 2002.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234, January
2008.
11.2. Informative References
[3GPP.22.519]
3GPP, "Business Communication Requirements", TS 22.519.
[3GPP.23.228]
3GPP, "IP Multimedia Subsystem (IMS); Stage 2", 3GPP TS
23.228 V8, July 2007.
[3GPP.24.229] 3GPP, "Internet Protocol (IP) multimedia call control
protocol based on Session Initiation Protocol (SIP) and
Session Description Protocol (SDP); Stage 3", 3GPP TS
24.229 V8, July 2007.
[RFC5727] Peterson, J., Jennings, C., and R. Sparks, "Change Process
for the Session Initiation Protocol (SIP) and the Real-
time Applications and Infrastructure Area", BCP 67, RFC
5727, March 2010.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, December 2005.
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Authors' Addresses
Hans Erik van Elburg
Detecon International Gmbh
Oberkasselerstrasse 2
Bonn 53227
Germany
EMail: ietf.hanserik@gmail.com
Keith Drage
Alcatel-Lucent
The Quadrant, Stonehill Green, Westlea
Swindon SN5 7DJ
UK
EMail: drage@alcatel-lucent.com
Mayumi Ohsugi
NTT Corporation
Phone: +81 422 36 7502
EMail: mayumi.ohsugi@ntt-at.co.jp
Shida Schubert
NTT Corporation
Phone: +1 415 323 9942
EMail: shida@ntt-at.com
Kenjiro Arai
NTT Corporation
9-11, Midori-cho 3-Chome
Musashino-shi, Tokyo 180-8585
Japan
Phone: +81 422 59 3518
EMail: arai.kenjiro@lab.ntt.co.jp
URI: http://www.ntt.co.jp
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