rfc2975.txt

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Network Working Group                                          B. Aboba
Request for Comments: 2975                        Microsoft Corporation
Category: Informational                                        J. Arkko
                                                               Ericsson
                                                          D. Harrington
                                                 Cabletron Systems Inc.
                                                           October 2000


                 Introduction to Accounting Management

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   The field of Accounting Management is concerned with the collection
   of resource consumption data for the purposes of capacity and trend
   analysis, cost allocation, auditing, and billing.  This document
   describes each of these problems, and discusses the issues involved
   in design of modern accounting systems.

   Since accounting applications do not have uniform security and
   reliability requirements, it is not possible to devise a single
   accounting protocol and set of security services that will meet all
   needs.  Thus the goal of accounting management is to provide a set of
   tools that can be used to meet the requirements of each application.
   This document describes the currently available tools as well as the
   state of the art in accounting protocol design.  A companion
   document, RFC 2924, reviews the state of the art in accounting
   attributes and record formats.













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Table of Contents

   1.  Introduction                                             2
       1.1   Requirements language                              3
       1.2   Terminology                                        3
       1.3   Accounting management architecture                 5
       1.4   Accounting management objectives                   7
       1.5   Intra-domain and inter-domain accounting          10
       1.6   Accounting record production                      11
       1.7   Requirements summary                              13
   2.  Scaling and reliability                                 14
       2.1   Fault resilience                                  14
       2.2   Resource consumption                              23
       2.3   Data collection models                            26
   3.  Review of Accounting Protocols                          32
       3.1 RADIUS                                              32
       3.2 TACACS+                                             33
       3.3 SNMP                                                33
   4.  Review of Accounting Data Transfer                      43
       4.1 SMTP                                                44
       4.2 Other protocols                                     44
   5.  Summary                                                 45
   6. Security Considerations                                  48
   7. Acknowledgments                                          48
   8. References                                               48
   9. Authors' Addresses                                       52
   10. Intellectual Property Statement                         53
   11. Full Copyright Statement                                54

1.  Introduction

   The field of Accounting Management is concerned with the collection
   of resource consumption data for the purposes of capacity and trend
   analysis, cost allocation, auditing, and billing.  This document
   describes each of these problems, and discusses the issues involved
   in design of modern accounting systems.

   Since accounting applications do not have uniform security and
   reliability requirements, it is not possible to devise a single
   accounting protocol and set of security services that will meet all
   needs.  Thus the goal of accounting management is to provide a set of
   tools that can be used to meet the requirements of each application.
   This document describes the currently available tools as well as the
   state of the art in accounting protocol design.  A companion
   document, RFC 2924, reviews the state of the art in accounting
   attributes and record formats.





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1.1.  Requirements language

   In this document, the key words "MAY", "MUST, "MUST NOT", "optional",
   "recommended", "SHOULD", and "SHOULD NOT", are to be interpreted as
   described in [6].

1.2.  Terminology

   This document frequently uses the following terms:

   Accounting
             The collection of resource consumption data for the
             purposes of capacity and trend analysis, cost allocation,
             auditing, and billing.  Accounting management requires that
             resource consumption be  measured, rated, assigned, and
             communicated between appropriate parties.

   Archival accounting
             In archival accounting, the goal is to collect all
             accounting data, to reconstruct missing entries as best as
             possible in the event of data loss, and to archive data for
             a mandated time period.  It is "usual and customary" for
             these systems to be engineered to be very robust against
             accounting data loss.  This may include provisions for
             transport layer as well as application layer
             acknowledgments, use of non-volatile storage, interim
             accounting capabilities (stored or transmitted over the
             wire), etc.  Legal or financial requirements frequently
             mandate archival accounting practices, and may often
             dictate that data be kept confidential, regardless of
             whether it is to be used for billing purposes or not.

   Rating    The act of determining the price to be charged for use of a
             resource.

   Billing   The act of preparing an invoice.

   Usage sensitive billing
             A billing process that depends on usage information to
             prepare an invoice can be said to be usage-sensitive.  In
             contrast, a process that is independent of usage
             information is said to be non-usage-sensitive.

   Auditing  The act of verifying the correctness of a procedure.  In
             order to be able to conduct an audit it is necessary to be
             able to definitively determine what procedures were
             actually carried out so as to be able to compare this to




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             the recommended process.  Accomplishing this may require
             security services such as authentication and integrity
             protection.

   Cost Allocation
             The act of allocating costs between entities.  Note that
             cost allocation and rating are fundamentally different
             processes.  In cost allocation the objective is typically
             to allocate a known cost among several entities.  In rating
             the objective is to determine the amount to be charged for
             use of a resource.  In cost allocation, the cost per unit
             of resource may need to be determined; in rating, this is
             typically a given.

   Interim accounting
             Interim accounting provides a snapshot of usage during a
             user's session.  This may be useful in the event of a
             device reboot or other network problem that prevents the
             reception or generation of a session summary packet or
             session record.  Interim accounting records can always be
             summarized without the loss of information.  Note that
             interim accounting records may be stored internally on the
             device (such as in non-volatile storage) so as to survive a
             reboot and thus may not always be transmitted over the
             wire.

   Session record
             A session record represents a summary of the resource
             consumption of a user over the entire session.  Accounting
             gateways creating the session record may do so by
             processing interim accounting events or accounting events
             from several devices serving the same user.

   Accounting Protocol
             A protocol used to convey data for accounting purposes.

   Intra-domain accounting
             Intra-domain accounting involves the collection of
             information on resource usage within an administrative
             domain, for use within that domain.  In intra-domain
             accounting, accounting packets and session records
             typically do not cross administrative boundaries.

   Inter-domain accounting
             Inter-domain accounting involves the collection of
             information on resource usage within an administrative





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             domain, for use within another administrative domain.  In
             inter-domain accounting, accounting packets and session
             records will typically cross administrative boundaries.

   Real-time accounting
             Real-time accounting involves the processing of information
             on resource usage within a defined time window.  Time
             constraints are typically imposed in order to limit
             financial risk.

   Accounting server
             The accounting server receives accounting data from devices
             and translates it into session records.  The accounting
             server may also take responsibility for the routing of
             session records to interested parties.

1.3.  Accounting management architecture

   The accounting management 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.  Session records may be batched and compressed by
   the accounting server prior to submission to the billing server in
   order to reduce the volume of accounting data and the bandwidth
   required to accomplish the transfer.

   One of the functions of the accounting server is to distinguish
   between inter and intra-domain accounting events and to route them
   appropriately.  For session records containing a Network Access
   Identifier (NAI), described in [8], the distinction can be made by
   examining the domain portion of the NAI.  If the domain portion is
   absent or corresponds to the local domain, then the session record is
   treated as an intra-domain accounting event.  Otherwise, it is
   treated as an inter-domain accounting event.




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   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.
   While it is not required that session record formats used in inter
   and intra-domain accounting be the same, this is desirable, since it
   eliminates translations that would otherwise be required.

   Where a proxy forwarder is employed, domain-based access controls may
   be employed by the proxy forwarder, rather than by the devices
   themselves.  The network device will typically speak an accounting
   protocol to the proxy forwarder, which may then either convert the