Patrik Olsson, Ericsson INTERNET-DRAFT Draft: Expires: April 2002 November, 2001 IP Multimedia Charging requirements on Diameter Accounting Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/lid-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This document is an individual submission to the IETF. Comments should be directed to the authors. Abstract The 3rd Generation Partnership Project (3GPP) are currently standardizing charging for 3GPP IP Multimedia Core Network Subsystem (IM CN Subsystem). One of the proposals for charging protocol is Diameter accounting. IP Multimedia will also be used in other network, both mobile and fixed networks and the operators needs proper charging mechanisms to bill the users. Olsson [Page 1] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 Although Diameter is a protocol that fulfills most of the requirements to collect accounting information, that can be used for charging, from the Multimedia nodes, the Diameter protocol has never been evaluated against the specific requirements for on-line charging in a cellular network. TABLE OF CONTENTS 1.0 Introduction 1.1 Requirements language 1.2 Terminology 1.3 Abbreviations 2.0 Charging and Accounting Principles 2.1 Telecom Charging in Cellular Network 2.2 IP Network Accounting 3.0 Overview of IP Multimedia network 4.0 IP Multimedia Charging Requirements on Diameter 4.1 General 4.2 On-line charging 4.3 One generic charging interface 4.4 IP Multimedia specific charging 4.4.1 Diameter IP multimedia Application 4.4.2 User Identities 4.4.3 SIP Call Id 4.4.4 SIP Messages 4.4.5 SDP data/Media information 4.4.6 Time-Stamp 4.4.7 Request-URI 4.4.8 Charging Correlation Id 4.4.9 QoS parameters 4.4.10 Multiparty calls 4.4.11 Call transfer, redirect and call forwarding 5.0 Security Considerations 6.0 Scalability Considerations 7.0 Author's Address 8.0 References 9.0 Fully Copyright Statement 1. Introduction This document is an effort to define the requirements applicable to the usage of the Diameter protocol [3] (Accounting part) for off-line and on-line charging in IP Multimedia networks. The rest of this document is structured as follows: Olsson [Page 2] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 Section 2 offers an overview of charging mechanisms in cellular networks and accounting principles in IP network. Section 3 contains the short description of charging in IP Multimedia networks. Section 4 contains the IP Multimedia charging requirements on Diameter accounting. Requirements are grouped by categories. Some requirements include a statement on possible solutions that would be able to fulfill the requirement. 1.1 Requirements language This document does not specify any protocol of any kind. Therefore, the use of the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document, as described in RFC-2119 [2], does not apply. 1.2 Terminology Accounting The act of collecting information on resource usage for the purpose of trend analysis, auditing, billing or cost allocation. Charging A function whereby information related to a chargeable event is transferred in order to make it possible to determine usage for which the charged party may be billed. This applies for all charging levels. Charging is one of the users of accounting. Accounting Server A network element that accepts Usage Events from Service Elements. It acts as an interface to back-end rating, billing, and operations support systems. Billing The functions whereby charging data are transformed into bills requiring payment. In case of pre-paid, billing means the deduction of an account. As an outcome of the transformation an invoice, including an optional list of detailed charges, has to be delivered to the user. Pre-paid billing Billing arrangement between customer and operator/service provider where the customer deposits an amount of money in advance, which is subsequently used to pay for service usage. Post-paid billing Olsson [Page 3] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 Billing arrangement between customer and operator/service provider where the customer periodically receives a bill for service usage in the past period. Note: Pre-paid and post-paid are different payment methods for the subscribers. These payment methods could be based on both on-line and off-line charging mechanisms. To get full credit control, pre- paid should be built on on-line charging. If the operator would like to have post-paid subscribers on credit control, these subscribers should be charged with the on-line charging mechanism. On-line Charging A charging process where charging information can affect, in real- time, the service rendered and therefore directly interacts with the session/service control. Note: Due to the real-time interaction between charging and session/service control, this mode requires a bi-directional interface that support on-line charging. Off-line Charging A charging process where charging information does not affect, in real-time, the service rendered. Note: No real-time interaction is required between charging and session/service control, but charging information may be delivered in real time or near real time. Call Data Record A formatted collection of information about a chargeable event (e.g. time of call set-up, duration of the call, amount of data transferred, etc) for use in billing and accounting. For each party to be charged for parts of or all charges of a chargeable event a separate CDR shall be generated, i.e. more than one CDR may be generated for a single chargeable event, e.g. because of its long duration, or because more than one charged party is to be charged. User Equipment A device allowing a user access to network services. For the purpose of 3GPP specifications the interface between the UE and the network is the radio interface. A User Equipment can be subdivided into a number of domains, the domains being separated by reference points. Currently defined domains are the USIM and ME Domains. 1.3 Abbreviations AAA: Authentication, Authorization and Accounting AS: Application Server Olsson [Page 4] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 AVP: Attribute Value Pair CDR: Call Data Record GPRS: General Packet Radio service IM CN: IP Multimedia Core Network ME: Mobile Equipment MM: Multimedia QoS: Quality of Service UE: User Equipment USIM: Universal Subscriber Identity Module 2.0 Charging and Accounting principles 2.1 Telecom Charging in Cellular Network In traditional cellular networks the subscriber charging and settlements between operators have been based on Off-line charging. The access network elements normally collect the charging data related to service usage to produce Call Data Record (CDR) after service usage has been completed in the serving network. These Call Data Records (CDR) are then transferred in batch mode to a billing systems in the serving network. The roaming subscriber's Call Data Records are sent from the visited network to the home network billing system. In addition to billing, Call Data Records are also used for fraud detection, statistic for trend analysis and network engineering, etc. During the last few years the On-line charging has become very popular. On-line charging mechanisms provide charging information from the access network nodes to a on-line charging function (for example a pre-paid system) in home. The charging information is sent from the access network nodes prior, during and after service usage. This allows the on-line charging function in home network to decide before or during service usage if the service in question shall be allowed to continue (Credit Control). On-line charging protocols such as the CAMEL Application Part (CAP) are used to support on-line charging mechanisms. Olsson [Page 5] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 Pre-paid and post-paid can be built on both on-line and off-line charging mechanisms, but to get full credit control of the subscriber, on-line charging must be used. 2.2 IP Network Accounting In IP network the accounting management [8] architecture involves interactions between network devices, accounting servers, and billing servers. The network device collects resource consumption data in the form of accounting metrics. This information is then transferred to an accounting server. Typically this is accomplished via an accounting protocol, although it is also possible for devices to generate their own session records. The accounting server then processes the accounting data received from the network device. This processing may include summarization of interim accounting information, elimination of duplicate data, or generation of session records. The processed accounting data is then submitted to a billing server, which typically handles rating and invoice generation, but may also carry out auditing, cost allocation, trend analysis or capacity planning functions. One of the functions of the accounting server is to distinguish between inter and intra-domain accounting events and to route them appropriately. Intra-domain accounting events are typically routed to the local billing server, while inter-domain accounting events will be routed to accounting servers operating within other administrative domains. 3.0 Overview of a IP Multimedia network This section gives the reader an overview of a IP Multimedia network from charging point of view. It is not intended to be comprehensive. But it provides enough information to understand the basis of the IP Multimedia charging. The IP Multimedia network is decomposed in a home network and a visited network. An IPMM Subsystem subscriber belongs to his or her home network. Home Network +----------+ | Charging | +-------->| Function |<--------+ Charging | |Accounting| | Charging Information | | Server | | Information Olsson [Page 6] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 v +----------+ v +--------+ +--------+ | Central| | Anchor | | SIP POC|<------------------->| SIP POC| | server | SIP | server | +--------+ +--------+ | | SIP | v +---------+ Visited Network | SIP POC | | server | | Visited | | Domain | +---------+ ^ | SIP | v +---------+ | SIP | | Client | +---------+ Figure 1: Functional Block Diagram The Charging Function (Which is an Accounting Server) is located in the Home Network, which will provide charging support for the home network subscribers. The multimedia Services are triggered and may be executed in the home network. Services are typically executed in an Application Server (AS). Authentication/Authorization servers may be part of the home network as well. Users are authenticated in the home network. The visited network contains the SIP POC Server. It is the first contact point from the SIP Client. It accepts requests and services internally or forwards them on, possibly after translation. At the home network the Central and Anchor SIP POC Servers are located. The Central SIP POC is the contact point within home network for all connections destined to a subscriber of that network. The Anchor SIP POC Server in the home network performs the session control services for the SIP Client. The IP multimedia network (in figure 1) in the home network is independent of the access and the Visited SIP POC server is the connection to the access network in some cellular networks. The Olsson [Page 7] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 visited SIP POC server canĘt provide more accounting/charging information the what can be get from the SIP POC servers in the home network. Accounting data to be used for charging should be collected from the home networks SIP servers. The way charging is performed for IP multimedia services differs significantly from traditional cellular networks. The main reason behind is that the following charging levels can occur for the IMS charging: a) Access Charging: The charging of usage of bearer resources. b) IP Multimedia session based charging: The charging of services provided by the IP Multimedia network. Typical example would be voice or video call with a certain QoS. c) Content based Charging: This means the charging for the provisioning of information, like Web pages or the sale of hard or soft goods. In Multimedia calls the signaling and the bearer normally don't follow the same path. Therefore, the basic principle is to handle charging for signaling and bearer separately. Charging based on signaling is done in the IP multimedia system, and charging for bearer usage is done in the access network. The charging based on content is performed by the Application Servers in the service platform. Charging for access is outside of the scope of this draft, but it must be considered when charging the user. 4.0 IP Multimedia Charging Requirements on Diameter 4.1 General The basic concept behind Diameter is to provide a base protocol that can be extended in order to provide AAA services to new applications. The base protocol is not intended to be used by itself, and must be used with a Diameter application. The Diameter accounting is part of base protocol and therefore it is not intended to be used without a Diameter application. The Diameter can provide two different types of services to applications. The first involves authentication and authorization, and can optionally make use of accounting. The second only make use of accounting. Diameter accounting protocol is based on server directed model with capabilities for real-time delivery of accounting information. Olsson [Page 8] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 The server directed model means that the instance generating the charging data gets information from either the authorization server (if contacted) or the accounting server regarding the way accounting data shall be forwarded. The Diameter accounting provides the way accounting information can be collected from certain applications, but it does not provide on- line charging. 4.2 On-line charging The Diameter accounting protocol provides real-time accounting meaning the processing of information on resource usage within a defined time window. Time constraints are typically imposed in order to limit financial risk. The next generation cellular networks specify more critical requirements for the on-line charging. The Accounting Server must be able to check the subscriber's account for coverage of the requested service charge prior to execution of that service. The subscriber's account shall be decreased each time the subscriber use the services related to that account and all the chargeable events related to a specific account shall be prevented from the subscriber when the credit of that account is exhausted or expired. Also a mechanism shall be provided to indicate to the subscriber of the charges to be levied for a chargeable event. This mechanism shall be able to handle all possible charging scenarios, and all service and tariff variants. The on-line charging support is needed from the Diameter accounting protocol. Before any service is allowed to the subscriber the service node acting as a client shall contact the home accounting server to request a credit for the event. If the subscriber is allowed to use the service, the home accounting server returns the granted amount of units for the service. When these units are used the Client can request the new amount of service unit to continue the service execution. After the service execution (and each interim request) the client informs the home accounting server about the used amount of the units. The granted unit type can be for example time (in seconds), volume (in Kbytes), events (as a number of executable events) or money (as a monetary value). The accounting server shall also return the accumulated cost of the session to the client and the total cost of the session at the end of the session. Olsson [Page 9] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 This requirement can be met for example by using the Diameter Credit Control Application described in [10]. 4.3 One generic charging interface There is a need as an option to offer also possibility not to generate CDRs in IP Multimedia nodes. The fact that a large number of subscribers require on-line charging (and the number is likely to grow) and the fact that on-line charging interface provides a large part of the data which is included in the Call Data Records, makes it feasible to combine on- and off-line charging into one generic charging interface. As described earlier the Diameter base protocol (and accounting part of it) is not intended to be used without a Diameter application. By using the Diameter accounting with the Diameter IP Multimedia application, which support both on-line and off-line charging, these requirement on one generic charging interface can be met. 4.4 IP Multimedia specific charging Depending on the role of the IP Multimedia node and if the node maintains the SIP session state, the on-line and/or off-line charging can be used. Author assumes that upon receipt of the SIP Invite method, but after optional authorization, the IP Multimedia node may initiate an on- line charging session. IP Multimedia node may also initiate one time event accounting records after the successful SIP registration. When charging for IP Multimedia session you also have to consider charging for the access network. How you charge for access is depending on the access network (for example GPRS, WLAN, ADSL). The Accounting information, which is needed, is listed in sub- chapters below. 4.4.1 Diameter IP Multimedia Application There will be a new Diameter IP Multimedia application, which shall also describe the accounting part of IP Multimedia. According to the principles define the Diameter base protocol each Diameter application must define their service specific AVPs that must be present in the Accounting messages. The Accounting messages from the base protocol shall be used. Olsson [Page 10] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 The Accounting parameters listed below shall be defined in this new Diameter IP Multimedia application as the IP Multimedia specific accounting AVPs. 4.4.2 User Identities Every user must have a user identities. The user identity/identities (Called-Party-Id and Calling-Party-Id) MAY take any form, for example SIP URL (as defined in SIP [4] and RFC2396 [5]) or the form of a TEL- URL/E.164 number [6] and [7]. 4.4.3 SIP Call Id The SIP Call Id [4] identifies uniquely a particular SIP invitation or all SIP registrations of a particular client. 4.4.4 SIP Messages The SIP server may generate an accounting messages for every SIP messages. It must be configurable in the SIP server if the accounting messages should be outputted. Examples of SIP messages are INVITE, BUSY, NO ANSWER, NOT AVAILABLE, REDIRECT. 4.4.5 SDP data/Media information The accounting messages must contain information about the media used. 4.4.6 Time-Stamp Time Stamp specifies the time when the SIP server generated the accounting-request. 4.4.7 Request-URI The Request URI [5] indicates the user or the service to which the request is being addressed. 4.4.8 Charging Correlation Id The Unique Charging Correlation Id is needed to be able to correlate the charging data from the different charging layers (IP Multimedia session and access network). The Charging Correlation Id must be globally unique throughout the session lifetime. It must by possible to correlate on a media in a SIP session with a specific bearer in the access network. 4.4.9 QoS parameters Olsson [Page 11] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 The accounting messages must contain information about the requested/negotiated quality of service. 4.4.10 Multiparty calls It the SIP call is a multiparty call, the accounting messages must contain information about involved parties (e.g. number of parties and identifiers of the involved parties). 4.4.11 Call transfer, redirect and call forwarding The operator must be able to charge for the different services, call transfer, redirect and call forwarding so relevant information must be outputted in the accounting messages. 5.0 Security considerations The Diameter base protocol [3] assumes that messages are secured by using either IP security, or TLS. This security model is acceptable in environments where there are no un-trusted third party relay, proxy or redirect servers. 6.0 Scalability considerations The IPMM diameter accounting application must scalable and work for networks with more the 10 million users. 7.0 Author's Addresses Patrik Olsson Tel: +46 455 395831 Ericsson Software Tech Mobile: +46 703 105831 Karlskrona, Sweden EMail: patrik.m.olsson@epk.ericsson.se 8.0 References 1. Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2. Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 3. P.Calhoun, H. Akhtar, J. Arkko, E. Guttman, A. Rubens, "Diameter Base Protocol", draft-ietf-aaa-diameter-07.txt, IETF work in progress, July 2001. 4. Handley M, Schulzrinne H, Schooler E, Rosenberg J., "SIP, Session Initiation Protocol", draft-ietf-sip-rfc2543bis-04.txt, Work in Progress. 5. T.Bernes-Lee, R.Fielding, L.Masinter, "Uniform Resource Identifiers (URI):Generic Syntax, RFC 2396, August 1998. 6. Recommendation E.164/I.331 (05/97): The International Public Telecommunication Numbering Plan. 1997. Olsson [Page 12] INTERNET-DRAFT IPMM Charging requirements on Diameter November, 2001 7. Complement to ITU-T recommendation E.164 (05/1997): List of ITU-T Recommendation E.164 assigned country codes", June 2000 8. B.Aboba, J.Arkko, D. Harrington, "Introduction to Accounting Management", RFC 2975, October 2000. 9. B. Aboba, M. Beadles, "The Network Access Identifier", RFC 2486, January 1999. 10. H. Hakala, "Diameter Credit Control Application", draft-hakala- Diameter-Credit-Control-00.txt, Work in Progress. 11. M. Handley, V. Jacobson, " SDP: Session Description Protocol", RFC 2327, April 1998. 12. M. Garcia et al. "3GPP requirements on SIP", draft-garcia-sipping- 3gpp-reqs-00.txt, Work in Progress. 9.0 Full Copyright Statement "Copyright (C) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." This Internet-Draft expires in April 2002. Olsson [Page 13]