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.

Copyright Notice

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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

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.

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.

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.

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].

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.

                     +------------------------------+
                     |       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).

                     +-------------------------------------------------+
                     |       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.)

                     +-------------------------------------------------+
                     |       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 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.

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.

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.
   
   [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.

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