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SIPPING                                                          D. York
Internet-Draft                                                     Voxeo
Intended status: Informational                                T. Asveren
Expires: September 4, 2010                                         Sonus
                                                           March 3, 2010


  P-Charge-Info - A Private Header (P-Header) Extension to the Session
                       Initiation Protocol (SIP)
                  draft-york-sipping-p-charge-info-08

Abstract

   This document describes 'P-Charge-Info', a private Session Initiation
   Protocol (SIP) header (P-header) used to convey billing information
   about the party to be charged.  This P-Header is currently in
   production usage by a number of equipment vendors and carriers and
   this document is submitted to request the registration of this header
   with IANA as required by section 4.2 of RFC 3427 and RFC 3968.  This
   P-Header may also be used in some situations to carry the ISUP Charge
   Number parameter for PSTN interconnection.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 4, 2010.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the



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   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 BSD License.


Table of Contents

   1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  4
   3.  Purpose of this Document . . . . . . . . . . . . . . . . . . .  4
   4.  Examples of the Problem  . . . . . . . . . . . . . . . . . . .  4
     4.1.  Use Case - Billing Identifier  . . . . . . . . . . . . . .  4
     4.2.  Use Case - ISUP Charge Number  . . . . . . . . . . . . . .  4
     4.3.  Use Case - Distributed Enterprise  . . . . . . . . . . . .  4
     4.4.  Use Case - Hosted Telephony Provider . . . . . . . . . . .  5
   5.  Alternatives . . . . . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  P-Charging-Vector  . . . . . . . . . . . . . . . . . . . .  6
     5.2.  P-DCS-Billing-Info . . . . . . . . . . . . . . . . . . . .  6
     5.3.  P-Asserted-Identity  . . . . . . . . . . . . . . . . . . .  7
   6.  The P-Charge-Info Header . . . . . . . . . . . . . . . . . . .  7
     6.1.  Applicability Statement for the P-Charge-Info header . . .  7
     6.2.  Usage of the P-Charge-Info header  . . . . . . . . . . . .  7
       6.2.1.  Procedures at the UA . . . . . . . . . . . . . . . . .  8
       6.2.2.  Procedures at the Proxy  . . . . . . . . . . . . . . .  8
     6.3.  Examples of Usage  . . . . . . . . . . . . . . . . . . . .  8
   7.  Formal Syntax  . . . . . . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
     9.1.  Trust Relationship . . . . . . . . . . . . . . . . . . . . 10
     9.2.  Untrusted Peers  . . . . . . . . . . . . . . . . . . . . . 10
       9.2.1.  Ingress from Untrusted Peers . . . . . . . . . . . . . 10
       9.2.2.  Egress to Untrusted Peers  . . . . . . . . . . . . . . 10
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   11. Changes  . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   12. Appendix A: NPI Parameter Values . . . . . . . . . . . . . . . 12
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     13.2. Informative References . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13




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1.  Overview

   In certain network configurations, it is desirable to decouple the
   identity of the caller (what is normally thought of as "Caller ID")
   from the identity/number used for billing purposes.  This document
   describes the current usage of 'P-Charge-Info', a private SIP header,
   to provide simple billing information and requests the registration
   of this header with IANA as required by section 4.2 of RFC 3427
   [RFC3427] and section 3 of RFC 3968 [RFC3968]..

   In a typical configuration, the identity of the caller, commonly
   referred to as "Caller ID" by end users, is derived from one of the
   following SIP headers:

   o  P-Asserted-Identity

   o  From (in the absence of P-Asserted-Identity)

   (NOTE: Some service providers today also use the "Remote-Party-ID"
   header but this was replaced by P-Asserted-Identity in RFC 3325.)

   This identity/number is typically presented to the receiving UA where
   it is usually displayed for the end user.  It is also typically used
   for billing purposes by the network entities involved in carrying the
   session.

   However, in some network configurations the "Caller ID" presented to
   the receiving UA may be different from the number desired to be used
   for billing purposes.

   For example, the "Caller ID" may not reflect the actual reality of
   the underlying network in terms of costs incurred on the PSTN.  This
   may result in excessive charging of one carrier by another based on
   the erroneous assumption that the call was originating from a
   different point on the PSTN.

   Another example would be where a gateway to the Public Switched
   Telephone Network (PSTN) receives the ISUP "Charge Number" in the
   PSTN signaling which designates the number to be billed.  The gateway
   needs to pass this information along to a SIP entity associated with
   billing.

   In both these examples, there exists a need for a way to pass an
   additional billing identifier that can be used between network
   entities in order to correctly bill for services.  At least one
   equipment provider, Sonus Networks, and several carriers have been
   using the "P-Charge-Info" header for the last 2-3 years as a simple
   mechanism to exchange this billing identifier.



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2.  Requirements Language

   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.


3.  Purpose of this Document

   This document has been prepared to comply with section 4.2 of RFC
   3427 [RFC3427] which states very clearly:

        All implemented P-headers SHOULD meet the P-Header requirements
        in 4.1.  Any P-header used outside of a very restricted research
        or teaching environment (such as a student lab on implementing
        extensions) MUST meet those requirements and MUST be documented
        in an RFC and be IANA registered.

   This document is submitted to comply with the process outlined in
   section RFC 3427 Section 4.1 and the registration requirements in
   Section 4.2.


4.  Examples of the Problem

4.1.  Use Case - Billing Identifier

   The simplest use case for P-Charge-Info could be an enterprise
   environment where each SIP endpoint has a direct number that is
   passed by the enterprise SIP proxy across to a SIP proxy at a SIP
   Service Provider who provides PSTN connectivity.  Rather than cause
   the SIP Service Provider to have to track each individual direct
   number for billing purposes, the enterprise SIP proxy could send in
   the P-Charge-Info header a single billing identifier that the SIP
   Service Provider uses for billing purposes.

4.2.  Use Case - ISUP Charge Number

   A second use case is one in which a PSTN gateway receives PSTN
   signaling that includes an ISUP Charge Number parameter and the PSTN
   gateway needs to send that ISUP Charge Number via SIP to other
   servers.  In this instance, the PSTN gateway will insert the ISUP
   Charge Number into the P-Charge-Info SIP header.

4.3.  Use Case - Distributed Enterprise

   A third and common use case is a large enterprise with a widely
   distributed SIP network to designate the specific point at which PSTN



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   interconnection occurs.  Consider an enterprise with a work force and
   offices distributed over a wide geographic area and linked by a
   common internal network over which voice traffic is sent.  Users
   across the network may be able to contact each other directly via SIP
   sessions, but there may only be a relatively few points in the
   network where interconnection occurs to the PSTN.  Consider this
   case:

   o  A branch office in Massachusetts has a series of IP phones that
      are connected via SIP to systems in the main office in Colorado
      and from there via SIP connections to the PSTN through a SIP
      service provider.

   o  The phones in the Massachusetts office have each been assigned a
      direct, local phone number in the US area code of 617.

   o  This local 617 phone number is presented to callers on the PSTN as
      the "Caller ID" based on its inclusion in the From and/or
      P-Asserted-Identity SIP headers.

   o  This local 617 phone number may also be used by the SIP service
      provider as the billing identifier and the call will be charged to
      the enterprise according to the relevant rates.

   o  However, the call actually connected to the PSTN via the SIP
      connection in the Colorado office where the USA area code is 303.

   Rather than use the direct numbers of each SIP endpoint for
   generating the billing information, the enterprise might choose to
   instead pass the SIP URI of the PSTN interconnection point in the
   P-Charge-Info header, either for simplicity or potentially to obtain
   better rates from the SIP service provider.

4.4.  Use Case - Hosted Telephony Provider

   Similar to the third use case of a large enterprise, a hosted
   telephony provider or hosted voice application provider may have a
   large SIP network with customers distributed over a very large
   geographic area using local market PSTN numbers but with only a very
   few actual PSTN interconnection points.

   As with the branch office earlier, the customer may have all local
   phone numbers yet outgoing calls are actually being routed across a
   SIP network and out specific PSTN gateways or across specific SIP
   connections to SIP service providers.  The hosted provider may want
   to pass a billing identifier to its SIP service providers again
   either for the purpose of simplicity in billing or to obtain better
   rates from the SIP service providers.



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5.  Alternatives

5.1.  P-Charging-Vector

   P-Charging-Vector is defined in section 4.6 of RFC 3455 [RFC3455] and
   used by the 3GPP to carry information related to the charging of a
   session.  There are, however, some differences in the semantics
   associated with P-Charging-Vector and P-Charge-Info.  P-Charging-
   Vector is mainly used to carry information for correlation of
   multiple charging records generated for a single session.  On the
   other hand, P-Charge-Info is used to convey information about the
   party to be billed for a call.  Furthermore, P-Charging-Vector has a
   mandatory icid-value parameter which is a globally unique value to
   identify the session for which the charging information is generated.
   Such a globally-unique identifier is not necessary when carrying
   information about the user to be billed when it is attached to the
   corresponding session-related signaling.

5.2.  P-DCS-Billing-Info

   P-DCS-Billing-Info is defined in section 7 of RFC 3603 [RFC3603] and
   used for passing billing information between trusted entities in the
   PacketCable Distributed Call Signaling Architecture.  For many
   billing situations, particularly the very large-scale residential
   telephone networks for which this header is designed, P-DCS-Billing-
   Info is an excellent solution.  However, this ability to address a
   range of situations adds complexity.  According to RFC 3603, each use
   of the P-DCS-Billing-Info header MUST include in the header the
   following:

   o  Billing-Correlation-ID, a globally unique identifier

   o  Financial-Entity-ID

   o  RKS-Group-ID (record keeping server

   and may include a variety of additional parameters.

   While this may work well in many billing scenarios, there are other
   billing scenarios that do not at all need this level of complexity.
   In those simpler scenarios all that is needed is simply a number to
   use for billing.  P-Charge-Info provides this simple solution for
   simple billing scenarios.

   Additionally, section 7.3 of RFC 3603 mandates that a UA MUST create
   a Billing-Correlation-ID and insert this into the P-DCS-Billing-Info
   header (along with the other required information) sent in the
   initial SIP INVITE.  This again makes sense for the residential



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   telephone service environment for which this header is designed.  In
   contrast, P-Charge-Info is designed to be used among proxies and not
   to be used at all by normal user agents.  (P-Charge-Info may, though,
   by used by user agents associated with PSTN gateways.)

5.3.  P-Asserted-Identity

   Early reviewers of this document asked why the "P-Asserted-Identity"
   header documented in RFC 3325 [RFC3325] could not be used.  As
   mentioned in the use case example above, P-Asserted-Identity is used
   to indicate the identity of the calling party.  However, in this
   instance, the requirement is to provide an additional identity of the
   SIP-to-PSTN interconnect point.

   It would be typical to find both P-Asserted-Identity and P-Charge-
   Info used in a SIP exchange.  P-Asserted-Identity would be used to
   provide the caller identity which would be displayed to the end user
   as "Caller ID" while P-Charge-Info would provide the billing
   identifier used for the billing associated with the call.


6.  The P-Charge-Info Header

6.1.  Applicability Statement for the P-Charge-Info header

   The P-Charge-Info header is applicable within a single private
   administrative domain or between different administrative domains
   where there is a trust relationship between the domains.

6.2.  Usage of the P-Charge-Info header

   The P-Charge-Info header is used to convey information about the
   identity of the party to be charged.  The P-Charge-Info header is
   typically inserted by one of the following:

   o  the SIP proxy on the originating network;

   o  a PSTN gateway acting as a SIP UA; or

   o  an application server generating billing information.

   P-Charge-Info is to be consumed by the SIP entity that provides
   billing services for a session.  This could be an entity generating
   billing records or an entity interacting with another enitity
   generating billing records.  Upon receipt of an INVITE request with
   P-Charge-Info header, such an entity SHOULD use the value present in
   the P-Charge-Info as indicating the party responsible for the charges
   associated with the session.



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6.2.1.  Procedures at the UA

   The P-Charge-Info header may be inserted by PSTN gateways or
   application servers acting as a SIP UA, either through local policy
   or as a result of information received via PSTN signaling, e.g. the
   Charge Number parameter in an ISUP IAM message.

   The P-Charge-Info header is not used/interpreted by a regular UA and
   should not normally be seen by such a UA.  If the header is
   transmitted to such a UA, the UA SHOULD ignore the header.

   A PSTN gateway or application server acting as a UA MAY use the
   content of the P-Charge-Info header present in an INVITE request it
   received for billing related procedures, e.g. in a billing record or
   during interaction with another entity generating billing records, as
   the identity of the party to be charged for the session.  A PSTN
   gateway or application server acting as a UA MAY use the content of
   the P-Charge-Info header to populate information about the identity
   of the party to charge in another type of signaling, e.g.  ISUP.

6.2.2.  Procedures at the Proxy

   A SIP proxy that supports this extension and receives a request,
   typically a SIP INVITE, without the P-Charge-Info header MAY insert a
   P-Charge-Info header.  The contents of the inserted header may be
   decided based on local policy or by querying an external entity to
   determine the identity of the party to be charged.

   A proxy MAY use the content of the P-Charge-Info header present in an
   INVITE request it received for billing related procedures, e.g. in a
   billing record or during interaction with another entity generating
   billing records.

   A SIP proxy that does not support this extension will pass any
   received P-Charge-Info header unmodified in compliance with RFC 3261.

   A proxy supporting this extension SHOULD remove the P-Charge-Info
   header before sending a request to a UA that is not acting as a PSTN
   gateway or appropriate application server.

6.3.  Examples of Usage

   The content of the P-Charge-Info header is typically simply a SIP URI
   used as a billing indicator.  As such, an example would be as simple
   as:

   P-Charge-Info: <sip:4075555555@1.2.3.4>




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   Any other applicable SIP URI could be used.

   P-Charge-Info optionally includes the additional parameters of the
   "Numbering Plan Indicator" and "Nature of Address".  These are used
   when the ISUP Charge Number value needs to be passed as part of
   P-Charge-Info.  For instance, this might be required in a SIP message
   for scenarios where SIP is used to connect two PSTN segments and
   needs to pass charging information between them.  An example of the
   usage of the optional header is:

   P-Charge-Info: <sip:6835555555@10.10.7.21>;npi=ISDN;noa=3


7.  Formal Syntax

   The Private Header specified in this document is described in both
   prose and an augmented Backus-Naur Form (BNF) defined in RFC 2234.
   Further, several BNF definitions are inherited from SIP and are not
   repeated here.  Implementors need to be familiar with the notation
   and contents of SIP [1] and RFC 2234 [3] to understand this document.

   The syntax of the P-Charge-Info header is described as follows:

         P-Charge-Info = "P-Charge-Info" HCOLON (name-addr / addr-spec)*
                 (SEMI charge-param)
                 ; name-addr and addr-spec are specified in RFC 3261
             charge-param = npi-param / noa-param / generic-param
             npi-param = "npi" EQUAL npi-value
                 ; generic-param is specifed in RFC 3261
             npi-value = ("UNKNOWN" / "ISDN" / "SPARE2" / "DATA" /
                 "TELEX" / "PRIVATE" / "SPARE6" / "SPARE7")
             noa-param = "noa" EQUAL noa-value
             noa-value = gen-value

   Additional information about the "npi-value" is in Appendix A.


8.  IANA Considerations

   This document defines a private SIP extension header field (beginning
   with the prefixe "P-").

   The extension is registered as a private extension field:

   RFC Number: RFCXXXX [Note to IANA: Please fill in with the RFC number
   of this specification.

   Header Field Name: P-Charge-Info



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   Compact Form: none


9.  Security Considerations

9.1.  Trust Relationship

   Given that the information contained in the P-Charge-Info header will
   be used for billing purposes the proxies and other SIP entities that
   share this information MUST have a trust relationship.

   If an untrusted entity were inserted between the trusted entities, it
   could potentially interfere with the billing records for the call.
   If the SIP connections are not made over a private WAN, a mechanism
   for securing the confidentiality and integrity of the SIP connection
   should be used to protect the information.  One such mechanism could
   be TLS-encryption of the SIP signaling stream.

9.2.  Untrusted Peers

9.2.1.  Ingress from Untrusted Peers

   If the P-Charge-Info header was accepted by a SIP entity from an
   untrusted peer, there is the potential for fraud if the untrusted
   entity sent incorrect information, either inadvertently or
   maliciously.

   Therefore a SIP entity MUST remove and ignore the P-Charge-Info
   header when it is received from an untrusted entity.

9.2.2.  Egress to Untrusted Peers

   If the P-Charge-Info header was sent by a SIP entity to an untrusted
   peer, there is the potential exposure of network information that is
   internal to a trust domain.  For instance, the untrusted entity may
   learn the identities of public SIP proxies used within the trust
   domain which could then potentially be directly attacked.

   Therefore a SIP entity MUST remove the P-Charge-Info header when it
   is sent to an untrusted entity.


10.  Acknowledgements

   The authors thank the following people for their comments, criticism,
   suggestions and assistance with ABNF notation: Keith Drage, Miguel
   Garcia, Christer Holmberg, Paul Kyzivat, Jonathan Rosenberg, Juha
   Heinanen and Sumit Garg.



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   For revision -05, the authors thank John Haluska who provided a range
   of comments and specific information related to interworking with the
   ISUP Charge Number.

   For revision -08, the authors thank Glen Wang who helped clarify the
   NPI parameter values with the reference to ANSI T1.113.


11.  Changes

   NOTE TO RFC EDITOR - Please remove this "Changes" section prior to
   publication.  Thank you.

   Revision -08 included the following modifications:

   o  The ABNF for the "npi-value" was modified to conform to the
      sequence of possible values stated in ANSI T1.113.

   o  An Appendix A was created listing the values from ANSI T1.113.

   Revision -07 was updated to the "trust200902" IPR statement and added
   references to RFC 3968.  At this point all comments have been
   incorporated and publication will be requested.

   Revision -06 had only a minor correction to the second usage example.
   The IPR statement was also updated to comply with RFC 5378.

   Revision -05 included the following modifications:

   o  The usage of P-Charge-Info for carrying the ISUP Charge Number
      parameter was formally incorporated into the draft.  Previous
      revisions had mentioned it as a possible use case but had not
      really explicitly included it.

   o  The examples/use cases section was expanded to include further
      examples of where P-Charge-Info may be used.

   o  The original use case which discussed inter/intra-state billing
      practices was changed as the geographical references were clouding
      the more fundamental issue.

   o  The "UNKNOWN" value was added to the ABNF for the "npi-value"
      parameter as that was identified as missing but required for ISUP
      interworking.

   o  The optional "Nature of Address" parameter was added to support
      interworking with the ISUP Charge Number.




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   Revision -04 corrected a major error in the example where the
   parameter was placed inside the angle brackets.  The P-DCS-Billing-
   Info header was also added as an alternative and a few minor edits
   were made.


12.  Appendix A: NPI Parameter Values

   To better understand the possible values for the optional NPI
   parameter, ANSI T1.113 states that the 'numbering plan indicator' may
   contain the following values:

          000 unknown (no interpretation)
          001 ISDN (Telephony) numbering plan (Recommendation E-164)
          010 spare (no interpretation)
          011 reserved (CCITT Data numbeting plan)
          100 reserved (CCITT Telex numbering plan)
          101 Private numbering plan
          110 spare (no interpretation)
          111 spare (no interpretation)


13.  References

13.1.  Normative References

   [RFC3427]  Mankin, A., Bradner, S., Mahy, R., Willis, D., Ott, J.,
              and B. Rosen, "Change Process for the Session Initiation
              Protocol (SIP)", BCP 67, RFC 3427, December 2002.

   [RFC3968]  Camarillo, G., "The Internet Assigned Number Authority
              (IANA) Header Field Parameter Registry for the Session
              Initiation Protocol (SIP)", BCP 98, RFC 3968,
              December 2004.

13.2.  Informative References

   [RFC3325]  Jennings, C., Peterson, J., and M. Watson, "Private
              Extensions to the Session Initiation Protocol (SIP) for
              Asserted Identity within Trusted Networks", RFC 3325,
              November 2002.

   [RFC3455]  Garcia-Martin, M., Henrikson, E., and D. Mills, "Private
              Header (P-Header) Extensions to the Session Initiation
              Protocol (SIP) for the 3rd-Generation Partnership Project
              (3GPP)", RFC 3455, January 2003.

   [RFC3603]  Marshall, W. and F. Andreasen, "Private Session Initiation



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              Protocol (SIP) Proxy-to-Proxy Extensions for Supporting
              the PacketCable Distributed Call Signaling Architecture",
              RFC 3603, October 2003.


Authors' Addresses

   Dan York
   Voxeo Corporation
   Keene, NH
   USA

   Phone: +1-407-455-5859
   Email: dyork@voxeo.com
   URI:   http://www.voxeo.com/


   Tolga Asveren
   Sonus Networks
   3 Paragon Way
   Freehold, NJ  07728
   USA

   Email: tasveren@sonusnet.com



























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