Network Working Group Bernard Aboba INTERNET-DRAFT Microsoft Corporation Category: Informational Jari Arkko <draft-aboba-acct-01.txt> Ericsson 8 June 1999 Introduction to Accounting Management 1. 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 to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. To view the list Internet-Draft Shadow Directories, see http://www.ietf.org/shadow.html. The distribution of this memo is unlimited. It is filed as <draft- aboba-acct-01.txt>, and expires December 1, 1999. Please send comments to the authors. 2. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. 3. 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. Aboba & Arkko Informational [Page 1]
INTERNET-DRAFT Accounting Management 8 June 1999 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, draft-brownlee-accounting-attributes-00.txt, reviews the state of the art in accounting attributes and record formats. 4. Table of Contents 1. Status of this Memo 2. Copyright notice 3. Abstract 4. Table of Contents 5. Introduction 5.1 Terminology 5.2 Accounting management architecture 5.3 Accounting management objectives 5.4 Intra-domain and inter-domain accounting 5.5 Requirements summary 6. Scaling and reliability properties of accounting systems 6.1 Fault resilience 6.2 Resource consumption 6.3 Data collection models 7. Review of existing accounting protocols 7.1 Accounting protocols 7.2 Accounting data transfer 8. Security issues 9. Acknowledgements 10. References 11. Authors' Addresses 12. Copyright Statement 13. Expiration date Aboba & Arkko Informational [Page 2]
INTERNET-DRAFT Accounting Management 8 June 1999 5. 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, draft-brownlee-accounting-attributes-00.txt, reviews the state of the art in accounting attributes and record formats. 5.1. 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. 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 Aboba & Arkko Informational [Page 3]
INTERNET-DRAFT Accounting Management 8 June 1999 non-usage-sensitive. Auditing The act of verifying the correctness of a procedure. 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 owed. In cost allocation, the cost per unit of resource may need to be determined; in rating, this is typically a given. Interim accounting An interim accounting packet provides a snapshot of usage during a user's session. It is typically implemented in order to provide for partial accounting of a user's session in the event of a device reboot or other network problem that prevents the reception of a session summary packet or session record. 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 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 of an entity with an administrative 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 Aboba & Arkko Informational [Page 4]
INTERNET-DRAFT Accounting Management 8 June 1999 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. 5.2. 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 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 the 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. While it is not required that session record formats used in inter and intra-domain accounting be the same, such rationalization is desirable, since it eliminates translations that would otherwise be required. Aboba & Arkko Informational [Page 5]
INTERNET-DRAFT Accounting Management 8 June 1999 The diagram below illustrates the accounting management architecture: +------------+ | | | Network | | Device | | | +------------+ | Accounting | Protocol | | | V +------------+ +------------+ | | | | | Org B | Inter-domain | Org A | | Acctg. |<----------------------------->| Acctg. | | Server | session records | Server | | | | | +------------+ +------------+ | | | Intra-domain | Transfer | session records | Protocol | | | | V V +------------+ +------------+ | | | | | Org B | | Org A | | Billing | | Billing | | Server | | Server | | | | | +------------+ +------------+ 5.3. Accounting management objectives Accounting Management involves the collection of resource consumption data for the purposes of capacity and trend analysis, cost allocation, auditing, and billing. Since each of these tasks have different requirements, we will discuss each task in detail. 5.3.1. Trend analysis and capacity planning In trend analysis and capacity planning, the goal is typically a forecast of future usage. Since such forecasts are inherently Aboba & Arkko Informational [Page 6]
INTERNET-DRAFT Accounting Management 8 June 1999 imperfect, high reliability is typically not required, and moderate data loss can typically be tolerated. In certain cases, it may be desirable to use statistical sampling techniques to reduce data collection requirements while still providing the forecast with the desired statistical accuracy. Such a sampling process may be insensitive even to large amounts of packet loss as long as bias is not introduced. The security requirements for trend analysis and capacity planning depend on the circumstances of data collection and the sensitivity of the data. Additional security services may be required when data is being transferred between administrative domains. For example, when information is being collected and analyzed within the same administrative domain, integrity protection and authentication may be used in order to guard against collection of invalid data. In inter- domain applications confidentiality may be desirable to guard against snooping by third parties. 5.3.2. Billing When accounting data is used for billing purposes, the requirements depend on whether the billing process is usage-sensitive or not. 5.3.2.1. Non-usage sensitive billing Since by definition, non-usage-sensitive billing does not require usage information, in theory all accounting data can be lost without affecting the billing process. Of course wholesale data loss will affect other tasks such as trend analysis or auditing, so that this would still cause problems. 5.3.2.2. Usage-sensitive billing Since usage-sensitive billing processes depend on usage information, packet loss may translate directly to revenue loss. As a result, the billing process may need to meet requirements arising from financial reporting standards, or legal requirements, and therefore an archival accounting approach may be required. Usage-sensitive systems may also have additional requirements relating to processing delay. Today credit risk is commonly managed by computerized fraud detection systems that are designed to detect unusual activity. While efficiency concerns might otherwise dictate batched transmission of accounting data, where it is desirable to minimize Aboba & Arkko Informational [Page 7]
INTERNET-DRAFT Accounting Management 8 June 1999 financial risk, a different approach may be required. Since financial exposure increases with processing delay, it may be necessary to transmit each event individually or to minimize batch size, to require positive acknowledgment before providing service, or even to utilize quality of service techniques to minimize queuing delays. The degree of financial exposure is application-dependent. For dialup Internet access from a local provider, charges are low and therefore the risk of loss is small. However, in the case of dialup roaming or voice over IP, time-based charges may be substantial and therefore the risk of fraud is larger. In such situations it is highly desirable to quickly detect unusual account activity, and it may be desirable for authorization to depend on ability to pay. In situations where valuable resources can be reserved, or where charges can be high, very large bills may be rung up quickly, and therefore real-time processing may be required. In usage-sensitive systems, accounting data may result in monetary transfers, and as a result, the security and reliability requirements are greater. Thus security services such as authentication and integrity protection are frequently used, and confidentiality and non-repudiation may also be desirable. 5.3.3. Auditing With enterprise networking expenditures on the rise, interest in auditing is increasing. Auditing, which is the act of verifying the correctness of a procedure, commonly relies on accounting data. Auditing tasks include verifying correctness of an invoice submitted by a service provider, or verification that usage is conforming to usage policy, service level agreements, or security guidelines. To permit a credible audit, the accounting data collection methods put in place must be at least as reliable as those used by the invoicing service provider. Similarly, security policies involved in auditing of an invoice should be at least as stringent as those used in preparation of the original invoice. Due to financial and legal requirements, archival accounting practices are frequently required in this application. Where auditing procedures are used to verify conformance to usage or security policies, security services may be desired. This typically will include integrity protection and authentication of accounting data, as well as confidentiality and possibly data object security. In order to permit response to security incidents in progress, auditing applications frequently are built to operate with low processing delay. Aboba & Arkko Informational [Page 8]
INTERNET-DRAFT Accounting Management 8 June 1999 5.3.4. Cost allocation The application of cost allocation and billback methods by enterprise customers is not yet widespread. However, with the convergence of telephony and data communications, there is increasing interest in applying cost allocation and billback procedures to networking costs, as is now commonly practiced with telecommunications costs. Cost allocation models, including traditional costing mechanisms described in [21]-[23] and activity-based costing techniques described in [24] are typically based on detailed analysis of usage data, and as a result they are almost always usage-sensitive. Whether cost allocation models are applied to allocation of costs between partners in a venture or to allocation of costs between departments in a single firm, cost allocation models often have profound behavioral and financial impacts. As a result, systems developed for this purposes are typically as concerned with reliable data collection and security as are billing applications. Due to financial and legal requirements, archival accounting practices are frequently required in this application. 5.4. Intra-domain and inter-domain accounting Much of the early work on accounting management focused on intra-domain accounting applications. However, with the increasing deployment of services such as dialup roaming, Internet fax, Internet telephony and QoS, applications requiring inter-domain accounting are becoming increasingly common. Inter-domain accounting differs from intra-domain accounting in several important ways. Intra-domain accounting involves the collection of information on resource consumption within an administrative domain, for use within that domain. In intra-domain accounting, accounting packets and session records typically do not cross administrative boundaries. As a result, intra-domain accounting applications typically experience low rates of packet loss and involve transfer of data between trusted entities. In contrast, inter-domain accounting involves the collection of information on resource consumption within an administrative domain, for use within another administrative domain. In inter-domain accounting, accounting packets and session records will typically cross administrative boundaries. As a result, inter-domain accounting applications may experience substantial packet loss. In addition, the entitities involved in the transfers cannot be assumed to trust each other. Aboba & Arkko Informational [Page 9]
INTERNET-DRAFT Accounting Management 8 June 1999 Since inter-domain accounting applications involve transfers of accounting data between domains, additional security measures may be desirable. In addition to authentication and integrity protection, it may be desirable to deploy security services such as confidentiality, replay protection, data object integrity, or non-repudiation. In inter- domain accounting each involved party also typically requires a copy of each accounting event for invoice generation and auditing. Aboba & Arkko Informational [Page 10]
INTERNET-DRAFT Accounting Management 8 June 1999 5.5. Requirements summary +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Usage | Intra-domain | Inter-domain | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Capacity | Robustness | Robustness | | Planning | against moderate | against high | | | packet loss | packet loss | | | | | | | Integrity, | Integrity, | | | authentication, | authentication, | | | replay protection | replay protection| | | [confidentiality] | confidentiality | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Non-Usage | Robustness against | Robustness | | Sensitive | packet loss not | against packet | | Billing | required | loss not | | | | required | | | | | | | Integrity, | Integrity, | | | authentication, | authentication, | | | replay protection | replay protection| | | [confidentiality] | confidentiality | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | | Archival | Archival | | Usage | accounting | accounting | | Sensitive | | | | Billing, | Integrity, | Integrity, | | Cost | authentication, | authentication, | | Allocation & | replay protection | replay protection| | Auditing | [confidentiality] | confidentiality | | | | [non-repudiation]| | | | | | | | [Bounds on | | | | processing delay]| | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Key [] = optional Aboba & Arkko Informational [Page 11]
INTERNET-DRAFT Accounting Management 8 June 1999 6. Scaling and reliability characteristics of accounting systems With the continuing growth of the Internet, it is important that accounting management systems be scalable and reliable. This section discusses the resources consumed by accounting management systems as well as the scalability and reliability properties exhibited by various data collection models. 6.1. Fault resilience As noted earlier, in applications such as usage-sensitive billing, cost allocation and auditing, an archival approach to accounting is frequently mandated, due to financial and legal requirements. Since in such situations loss of accounting data can translate directly into revenue loss, financial incentives exist to engineer a high degree of fault resilience. Faults which may be encountered include: Packet loss Accounting server failures Network failures Device reboots To date, much of the debate on accounting reliability has focussed on resilience against packet loss and the differences between UDP and TCP- based transport. However, it should be understood that resilience against packet loss is only one aspect of the program required to meet archival accounting requirements. As noted in [43], "once the cable is cut you don't need more retransmissions, you need a *lot* nore voltage." Thus, the choice of UDP or TCP transport has no impact on resilience against faults such as network partition, accounting server failures or device reboots. What does provide resilience against these faults is non-volatile storage. The importance of non-volatile storage in design of reliable accounting systems cannot be over-emphasized. Without such storage, event-driven systems will lose data once the transmission timeout has been exceeded, and polling or event-driven batching designs will experience data loss once the internal memory used for event storage has been exceeded. Thus, it may be plausibly argued that non-volatile storage is more important to accounting reliability than network connectivity, since for many years reliable accounting systems were implemented based solely on physical storage, without any network connectivity. For example, phone usage data used to be stored on paper, film, or magnetic media and carried from the place of collection to a central location for bill processing. Aboba & Arkko Informational [Page 12]
INTERNET-DRAFT Accounting Management 8 June 1999 6.1.1. Interim accounting Interim accounting provides protection against loss of session summary data by providing checkpoint information that can be used to reconstruct the session record in the event that the session summary information is lost. This technique may be applied to any data collection model (i.e. event-driven or polling) and is supported in both RADIUS [25] and in TACACS+ [26]. While interim accounting can provide resilience against packet loss, server failures, short-duration network failures, or device reboot, its applicability is limited. Since most packet loss on the Internet is due to congestion, sending interim accounting data over the wire can actually make the problem worse by increasing bandwidth usage. As a result, on-the-wire interim accounting is best restricted to use with high-value accounting data such as information on long-lived sessions. To protect against loss of data on such sessions, the interim reporting interval is typically set several standard deviations larger than the average session duration. This ensures that most sessions will not result in generation of interim accounting events and the additional bandwidth consumed by interim accounting will be moderate. However, as the interim accounting interval decreases toward the the average session time, the additional bandwidth consumed by interim accounting increases markedly, and as a result, the interval must be set with caution. This practice is particularly suspect since it increases use of network bandwidth in normal operation, while providing benefits only in the event of a fault. Where non-volatile storage is unavailable, interim accounting can also result in excessive consumption of memory that could be better allocated to storage of session data. As a result, implementors should be careful to ensure that new interim accounting data overwrites previous data rather than accumulating additional interim records thereby worsening the buffer exhaustion problem. Given the decreasing cost of non-volatile memory, it may be preferable to store interim accounting data in non-volatile storage. Stored interim events are then replaced by session data when the session completes, and the session data can itself be erased once the data has been transmitted. This approach avoids interim data being transmitted over the wire, except in the case of a device reboot. 6.1.2. Packet loss As packet loss is a fact of life on the Internet, accounting protocols need to be resilient against such losses. This is particularly important Aboba & Arkko Informational [Page 13]
INTERNET-DRAFT Accounting Management 8 June 1999 in inter-domain accounting, where packets often pass through Network Access Points (NAPs) where packet loss may be substantial. Resilience against packet loss can be accomplished via implementation of a retry mechanism on top of UDP, or use of TCP. On-the-wire interim accounting provides only limited benefits in mitigating the effects of packet loss. When implementing UDP retransmission, there are a number of issues to keep in mind: Retry behavior Congestion control Timeout behavior In designing a UDP retry mechanism, it is important that the retry timers relate to the round-trip time, so that retransmissions will not typically occur within the period in which acknowledgements may be expected to arrive. Accounting bandwidth may be significant in some circumstances, so that the added traffic due to unnecessary retransmissions may increase congestion levels. Congestion control in accounting data transfer is a somewhat controversial issue. Since accounting traffic is often considered mission-critical, it has been argued that congestion control is not a requirement; better to let other less-critical traffic back off in response to congestion. Moreover, without non-volatile storage, congestive backoff in accounting applications can result in data loss due to buffer exhaustion. However, there are very persuasive arguments that in modern accounting implementations, it is possible to implement congestion control while improving throughput and maintaining high reliability. In circumstances where there is sustained packet loss, there simply is not sufficient capacity to maintain existing transmission rates. Thus, aggregate throughput will actually improve if congestive backoff is implemented. This is due to elimination of retransmissions and ability to utilize techniques such as RED to desynchronize flows. In addition, with QoS mechanisms such as differentiated services, it is possible to mark accounting packets for preferential handling so as to provide for lower packet loss if desired. Thus such choices need not be hard coded within the application, but can be left to the network administrator. Furthermore, systems implementing non-volatile storage allow for backlogged accounting data to be placed in permanent storage pending transmission so that buffer exhaustion resulting from congestive backoff is not a concern. Since UDP is not really a transport protocol, UDP-based accounting protocols such as [4] often do not prescribe timeout behavior. Thus one Aboba & Arkko Informational [Page 14]
INTERNET-DRAFT Accounting Management 8 June 1999 implementation may throw the accounting data away after 3 constant duration retries to the same server, while another may implement exponential backoff to a given server, then switch to another server, up to a total timeout interval of 12 hours, while storing the untransmitted data on non-volatile storage. The difference between these behaviors may be of intense concern, since the former approach will not satisfy archival accounting requirements while the latter may. 6.1.3. Accounting server failures In the event of an accounting server failure, it may not be possible for a device to transmit accounting data to its primary accounting server. For protocols using TCP, opening of a connection to the secondary accounting server can occur after a timeout or loss of the primary connection, or it can occur on expiration of a timer. For protocols using UDP, transmission to the secondary server can occur after a number of retries or timer expiration. In either case, it is possible for the primary and secondary accounting servers to receive the same record, so that elimination of duplicates is required. Since accounting server failures can result in data accumulation on accounting clients, use of non-volatile storage can ensure against the loss of such data due to transmission timeouts or buffer exhaustion. On-the-wire interim accounting provides only limited benefits in mitigating the effects of accounting server failures. 6.1.4. Network failures Network failures may result in partial or complete loss of connectivity for the accounting client. In the event of partial connectivity loss, it may not be possible to reach the primary accounting server, in which case switchover to the secondary accounting server is necessary. In the event of a network partition, it may be necessary to store accounting events in device memory or non-volatile storage until connectivity can be re-established. As with accounting server failures, on-the-wire interim accounting provides only limited benefits in mitigating the effects of network failures. 6.1.5. Device reboots In the event of a device reboot, it is desirable to minimize the loss of data on sessions in progress. Such losses may be significant even if the Aboba & Arkko Informational [Page 15]
INTERNET-DRAFT Accounting Management 8 June 1999 devices themselves are very reliable, due to long-lived sessions, which can comprise a significant fraction of total resource consumption. Sending interim accounting data over the wire is typically implemented to guard against loss of these high-value sessions. When interim accounting is combined with non-volatile storage it becomes possible to guard against data loss in much shorter sessions. This is possible since interim accounting data need only be stored in non-volatile memory until the session completes, at which time the interim data may be replaced by the session record. As a result, interim accounting data need never be sent over the wire, and it is possible to decrease the interim interval so as to provide a very high degree of protection against data loss. Aboba & Arkko Informational [Page 16]
INTERNET-DRAFT Accounting Management 8 June 1999 6.1.6. Fault resilience summary +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Fault | Counter-measures | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Packet | Retransmission based on RTT | | loss | Congestion control | | | Well-defined timeout behavior | | | Duplicate elimination | | | Interim accounting* | | | Non-volatile storage | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Accounting | Primary-secondary servers | | server & net | Duplicate elimination | | failures | Interim accounting* | | | Non-volatile storage | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Device | Interim accounting* | | reboots | Non-volatile storage | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Key * = limited usefulness without non-volatile storage 6.2. Resource consumption In the process of growing to meet the needs of providers and customers, accounting management systems consume a variety of resources, including: Network bandwidth Memory Non-volatile storage State on the accounting management system CPU on the management system and managed devices In order to understand the limits to scaling of accounting management systems, we examine each of these resources in turn. Aboba & Arkko Informational [Page 17]
INTERNET-DRAFT Accounting Management 8 June 1999 6.2.1. Network bandwidth Accounting management systems consume network bandwidth in the transferring of accounting data. The network bandwidth consumed is proportional to the amount of data transferred, as well as required network overhead. Since accounting data for a given event may be 100 octets or less, if each event is transferred individually, overhead can represent a considerable proportion of total bandwidth consumption. As a result, it is often desirable to transfer accounting data in batches, enabling network overhead to be spread over a larger payload, and enabling efficient use of compression. 6.2.2. Memory In accounting systems without non-volatile storage, accounting data must be stored in volatile memory during the period between when it is generated and when it is transferred. The resulting memory consumption will depend on retry and retransmission algorithms. Since systems designed for high reliability will typically wish to retry for long periods, or may store interim accounting data, the resulting memory consumption can be considerable. As a result, if non-volatile storage is unavailable, it may be desirable to compress accounting data awaiting transmission. As noted earlier, implementors of interim accounting should take care to ensure against excessive memory usage by overwriting older interim accounting data with newer data for the same session rather than accumulating interim data in the buffer. 6.2.3. Non-volatile storage Since accounting data stored in memory will typically be lost in the event of a device reboot or a timeout, it may be desirable to provide non-volatile storage for undelivered accounting data. With the costs of flash RAM declining rapidly, it is likely that network devices will be capable of incorporating non-volatile storage within the next few years. As described in [11], non-volatile storage may be used to store interim or session records in a standard ASCII format. As with memory utilization, interim accounting overwrite is desirable so as to prevent excessive storage consumption. Note that the use of ASCII data representation enables use of highly efficient text compression algorithms that can minimize storage requirements. Such compression algorithms are only typically applied to session records so as to enable implementation of interim data overwrite. Aboba & Arkko Informational [Page 18]
INTERNET-DRAFT Accounting Management 8 June 1999 6.2.4. State on the accounting management system In order to keep track of received accounting data, accounting management systems may need to keep state on managed devices or concurrent sessions. Since the number of devices is typically much smaller than the number of concurrent sessions, it is desirable to keep only per-device state if possible. 6.2.5. CPU requirements CPU consumption of the managed and managing nodes will be proportional to the complexity of the required accounting processing. Operations such as ASN.1 encoding and decoding, compression/decompression, and encryption/decryption can consume considerable resources, both on accounting clients and servers. The effect of these operations on accounting system reliability should not be under-estimated, particularly in the case of devices with moderate CPU resources. In the event that devices are over-taxed by accounting tasks, it is likely that overall device reliability will suffer. Aboba & Arkko Informational [Page 19]
INTERNET-DRAFT Accounting Management 8 June 1999 6.2.6. Efficiency measures +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Resource | Efficiency measures | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Network | Batching | | Bandwidth | Compression | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Memory | Compression | | | Interim accounting overwrite | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | Non-volatile | Compression | | Storage | Interim accounting overwrite | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | System | Per-device state | | state | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | CPU | Hardware assisted | | requirements | compression/encryption | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 6.3. Data collection models Several data collection models are currently in use today for the purposes of accounting data collection. These include: Polling model Event-driven model Event-driven polling model 6.3.1. Polling model In the polling model, an accounting manager will poll devices for accounting information at regular intervals. In order to ensure against Aboba & Arkko Informational [Page 20]
INTERNET-DRAFT Accounting Management 8 June 1999 loss of data, the polling interval will need to be shorter than the maximum time that accounting data can be stored on the polled device. For devices without non-volatile stage, this is typically determined by available memory; for devices with non-volatile storage the maximum polling interval is determined by the size of non-volatile storage. The polling model results in an accumulation of data within individual devices, and as a result, data is typically transferred to the accounting manager in a batch, resulting in an efficient transfer process. In terms of Accounting Manager state, polling systems scale with the number of managed devices, and system bandwidth usage scales with the amount of data transferred. Without non-volatile storage, the polling model results in loss of accounting data due to device reboots, but not due to packet loss or network failures of sufficiently short duration to be handled within available memory. This is because the Accounting Manager will continue to poll until the data is received. In situations where operational difficulties are encountered, the volume of accounting data will frequently increase so as to make data loss more likely. However, in this case the polling model will detect the problem since attempts to reach the managed devices will fail. The polling model is typically not appropriate for implementation of roaming services, including wireless data, internet telephony, QoS provisioning or Internet access. This is because in order to retrieve accounting data on roaming users, the Accounting Management station would need to periodically poll the devices of all potential roaming partners, most of which would not hold any relevant data. Per-device state is typical of polling-based network management systems, which often also carry out accounting management functions, since network management systems need to keep track of the state of network devices for operational purposes. 6.3.2. Event-driven model In the event-driven model, a device will contact the accounting server or manager when it is ready to transfer accounting data. Most event- driven accounting systems, such as those based on RADIUS accounting, described in [4], transfer only one accounting event per packet, which is inefficient. Without non-volatile storage, a pure event-driven model only stores individual accounting events that have not yet been delivered and as a result it has the smallest memory requirements of any of the models. However, the event-driven model is also the least reliable, since Aboba & Arkko Informational [Page 21]
INTERNET-DRAFT Accounting Management 8 June 1999 accounting data loss will occur due to device reboots, sustained packet loss, or network failures of duration greater than the timeout interval. Since accounting servers will not receive events if operational difficulties are encountered, event-driven accounting systems are not very useful in monitoring of device health. The event-driven model is frequently used for implementation of roaming services, since this model allows accounting data to be sent to the roaming partners with low processing delay. This permits application of fraud prevention techniques. However, because roaming accounting events are frequently of high value, the poor reliability of this model is an issue. As a result, the event-driven polling model may be more appropriate. Per-session state is typical of event-driven systems without batching, and as a result, a pure event-driven approach is to be avoided wherever possible. 6.3.3. Event-driven polling model In the event-driven polling model an accounting manager will poll the device for accounting data only when it receives an event. The accounting client can generate an event when a batch of a given size has been gathered, when data of a certain type is available or after a minimum time period has elapsed. Note that while transfer efficiency will increase with batch size, without non-volatile storage, the potential data loss from a device reboot will also increase. Without non-volatile storage, an event-driven polling model will lose data due to device reboots, but not due to packet loss, or network partitions of short-duration. Unless a minimum delivery interval is set, event-driven polling systems are not useful in monitoring of device health. The event-driven polling model can be highly suitable for use in roaming since it permits accounting data to be sent to the roaming partners with low processing delay. At the same time non-roaming accounting can be handled via more efficient polling techniques, thereby providing the best of both worlds. Where batching can be implemented the state required in event-driven polling can be reduced to scale with the number of active devices. If portions of the network vary widely in usage, then this state may actually be less than that of the polling approach. Aboba & Arkko Informational [Page 22]
INTERNET-DRAFT Accounting Management 8 June 1999 6.3.4. Data collection summary +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Model | Pros | Cons | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Polling | Per-device state | Not robust | | | Robust against | against device | | | packet loss | reboot, server | | | Batch transfers | or network | | | | failures* | | | | Polling interval | | | | determined by | | | | storage limit | | | | High processing | | | | delay | | | | Unsuitable for | | | | use in roaming | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Event-driven | Low processing | Not robust | | | delay | against packet | | | Suitable for | loss, device | | | use in roaming | reboot, or | | | | network | | | | failures* | | | | Low efficiency | | | | Per-session state| | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Event-driven | Low processing | Not robust | | polling | delay | against device | | | Suitable for use | reboot, network | | | in roaming | failures* | | | Batch transfers | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Key * = non-volatile storage needed to address this Aboba & Arkko Informational [Page 23]
INTERNET-DRAFT Accounting Management 8 June 1999 7. Review of existing accounting protocols Accounting systems have been successfully implemented using protocols such as RADIUS, TACACS+, and SNMP. This section describes the characteristic of each of these protocols, as well as transfer protocols such as HTTP, FTP, and SMTP. For a review of accounting attributes and record formats, see [45]. 7.1. Accounting protocols 7.1.1. RADIUS RADIUS accounting, described in [4], was developed as an add-on to the RADIUS authentication protocol, described in [3]. As a result, RADIUS accounting shares the event-driven approach of RADIUS authentication, without support for batching or polling. As a result, RADIUS accounting scales with the number of accounting events instead of the number of devices, and accounting transfers are inefficient. In addition, since RADIUS accounting is based on UDP and timeout and retry parameters are not specified, implementations vary widely in their approach to reliability, with some implementations retrying until delivery or buffer exhaustion, and others losing accounting data after a few retries. As a result, RADIUS accounting implementations are vulnerable to packet loss as well as network failures and device reboots. These deficiencies are magnified when RADIUS accounting is applied in inter-domain accounting as is required in roaming, as noted in [1] and [2]. On the other hand, the event-driven approach of RADIUS accounting is well suited to handling of accounting events which require low processing delay, such as is required for credit risk management or fraud detection. While RADIUS accounting does provide hop-by-hop authentication and integrity protection, and IPSEC can be employed to provide hop-by-hop confidentiality, data object security is not supported, and thus systems based on RADIUS accounting are not capable of being deployed with untrusted proxies, or in situations requiring non-repudiation, as noted in [2]. While in principle extensible with the definition of new attributes, RADIUS suffers from the very small standard attribute space (256 attributes). Aboba & Arkko Informational [Page 24]
INTERNET-DRAFT Accounting Management 8 June 1999 7.1.2. TACACS+ TACACS+ as defined in [26] offers an accounting model with start, stop, and interim update messages. Since TACACS+ is based on TCP, implementations are typically resilient against packet loss and short- lived network partitions, and TACACS+ scales with the number of devices. TACACS+ does not support batching, and as a result, is suitable for handling of accounting events that require moderate though not the lowest processing delay, since it runs over TCP. TACACS+ provides for hop-by-hop authentication and integrity protection as well as hop-by-hop confidentiality. Data object security is not supported, and therefore systems based on TACACS+ accounting are not deployable in the presence of untrusted proxies. TACACS+ does not support non-repudiation. 7.1.3. SNMP SNMP, described in [27]-[41], has been widely deployed in a wide variety of intra-domain accounting applications, typically using the polling data collection model. Since polling allows data to be collected on multiple accounting events simultaneously, this model results in per- device state, and supports batch transfers for high efficiency, thus improving scaling properties and enabling efficient transfers. Since the management agent is able to retry requests when a response is not received, such systems are resilient against packet loss or even short- lived network partitions. While polling implementations without non- volatile storage can only store accounting events up to the limits of their memory, and thus are not robust against device reboots or network failures, when combined with non-volatile storage, they can be made highly reliable. Thus, addition of support for file-based storage and subsequent transfer of SNMP-based accounting data is highly desirable. File-based storage of SNMP data is described in [43], and an FTP MIB is described in [44]. Although with SNMP v2 it is also possible support confirmed notifications, so as to implement an event-driven polling model, we are not aware of any SNMP-based accounting systems that make use of this facility. With SNMPv3, it is possible to incorporate view-based access controls, described in [40], as well as user-based security, described in [38]. As a result, SNMP v3-based accounting implementations can provide for hop-by-hop authentication, integrity and replay protection, confidentiality and access-control. They cannot however provide data- object based security required for deployment with untrusted proxies, nor does SNMPv3 support non-repudiation. Aboba & Arkko Informational [Page 25]
INTERNET-DRAFT Accounting Management 8 June 1999 Where multiple administrative domains are involved, such as in the shared use networks and roaming associations described in [1], more sophisticated access controls are often required. Since in shared use networks the same device may be accessed by multiple organizations, it is often necessary to control access to accounting data according to the user's organization. This ensures that organizations may be given access to accounting data relating to their users, but not to data relating to users of other organizations. This implies that access rights will depend not only on the element being collected, but on the identity of the user to whom that data relates. Through use of the contextName, it is possible to run multiple copies of an SNMP MIB, one for each accessing organization or context. This permits access to be controlled using the view-based access control model described in [40]. However, as the number of network devices within the shared use or roaming network grows, the polling model of data collection becomes increasingly impractical since most devices will not carry data relating to the polling organization. As a result, shared-use networks or roaming associations relying on SNMP-based accounting have generally collected data for all organizations and then sorted the resulting session records for delivery to each organization. While functional, this approach will typically result in increased processing delay as the number of organizations and data records grows. 7.2. Accounting data transfer In order for session records to be transmitted between accounting servers, a transfer protocol is required. Transfer protocols in use today include SMTP, FTP, and HTTP. 7.2.1. SMTP-based accounting record transfer To date, few accounting management systems have been built on SMTP since the implementation of a store-and-forward message system has traditionally required access to non-volatile storage which has to date not been widely available on network devices. However, an examination of the characteristics of SMTP-based implementations reveals that they possess many desirable characteristics. Accounting management systems using SMTP for accounting transfer will typically support batching so that message processing overhead will be spread over multiple accounting records. As a result, these systems result in per-active device state. Since accounting systems using SMTP as a transfer mechanism have access to substantial non-volatile storage, they can generate, compress if necessary, and store accounting records until they are transferred to the collection site. As a result, Aboba & Arkko Informational [Page 26]
INTERNET-DRAFT Accounting Management 8 June 1999 accounting systems implemented using SMTP can be highly efficient and scalable. Using IPSEC, TLS or Kerberos, hop-by-hop security services such as authentication, integrity protection and confidentiality can be provided. As described in [13] and [15], data object security is available for SMTP, and in addition, the facilities described in [12] make it possible to request and receive signed receipts, which enables non-repudiation as described in [12]-[18]. As a result, accounting systems utilizing SMTP for accounting data transfer are capable of satisfying the most demanding security requirements. However, such systems are not typically capable of providing low processing delay, although this may be addressed by the enhancements described in [20]. 7.2.2. Other transfer mechanisms File transfer protocols such as FTP and HTTP have been used for transfer of accounting data. For example, Reference [9] describes a means for representing ASN.1-based accounting data for storage on archival media. Through the use of the Bulk File MIB, described in [43], accounting data from an SNMP MIB can be stored in ASN.1, bulk binary or Bulk ascii format, and then subsequently retrieved as required using the FTP Client MIB described in [44]. Given access to sufficient non-volatile storage, accounting systems based on record formats and transfer protocols can avoid loss of data due to long-duration network partitions, server failures or device reboots. Since it is possible for the transfer to be driven from the collection site, the collector can retry transfers until successful, or with HTTP may even be able to restart partially completed transfers. As a result, file transfer-based systems can be made highly reliable, and the batching of accounting records makes possible efficient transfers and application of required security services with lessened overhead. 8. Security issues As noted previously in this document, accounting applications vary in their security and reliability requirements. Some uses such as capacity planning may only require authentication, integrity and replay protection, and modest reliability while other applications such as inter-domain usage-sensitive billing may require the highest degree of security and reliability, since in these cases the transfer of accounting data will lead directly to the transfer of funds. Since accounting applications do not have uniform security and reliability requirements, it is not possible to devise a single Aboba & Arkko Informational [Page 27]
INTERNET-DRAFT Accounting Management 8 June 1999 accounting protocol and set of security services that will meet all needs. Rather, the goal of accounting management should be to provide a set of tools that can be used to construct accounting systems meeting the requirements of an individual application. As a result, it is important to analyze a given accounting application to ensure that the methods chosen meet the security and reliability requirements of the application. Based on the analysis given previously, it appears that existing protocols are capable of meeting the security requirements for capacity planning and non-usage sensitive billing applications. For usage sensitive billing, as well as cost allocation and auditing applications, new work is required to support the file- based storage and transfer of bulk data needed to ensure high reliability. For time sensitive applications such as those supporting fraud detection or roaming, no existing protocol simultaneously meets the requirements for high security and reliability, as well as low processing delay. A summary is given below: Aboba & Arkko Informational [Page 28]
INTERNET-DRAFT Accounting Management 8 June 1999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Usage | Intra-domain | Inter-domain | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Capacity | SNMP v3 | SNMP v3 w/ | | Planning | TACACS+ accounting | contextName | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | Non-Usage | SNMP v3 | SNMP v3 w/ | | Sensitive | RADIUS accounting | contextName | | Billing | DIAMETER accounting| | | | TACACS+ accounting | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | | Session record | Session record | | Usage | storage and | storage | | Sensitive | file transfer | and file transfer| | Billing, | via secure | via ultra- | | cost | protocol | secure protocol | | allocation & | (i.e. FTP or HTTP | (i.e. S/MIME- | | auditing | over TLS) | based EDI with | | (no time | | receipts) | | sensitivity or | | | | roaming) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | | Low overhead, | Low overhead, | | Time | event driven | event driven | | Sensitive | polling with | polling with | | Billing, | authenticity | data object | | fraud | and privacy | security and | | detection, | support | receipt support | | roaming | | | | | No existing | No existing | | | protocol | protocol | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 9. Acknowledgements The authors would like to thank Jan Melen (Ericsson), Jarmo Savolainen (Ericsson), and Glen Zorn (Microsoft) for many useful discussions of Aboba & Arkko Informational [Page 29]
INTERNET-DRAFT Accounting Management 8 June 1999 this problem space. 10. References [1] Aboba, B., Lu J., Alsop J., Ding J., and W. Wang, "Review of Roaming Implementations", RFC 2194, September 1997. [2] Aboba, B., and G. Zorn, "Criteria for Evaluating Roaming Protocols", RFC 2477, January 1999. [3] Rigney, C., Rubens, A., Simpson, W., Willens, S., "Remote Authentication Dial In User Service (RADIUS)", RFC 2138, April, 1997. [4] Rigney, C., "RADIUS Accounting", RFC 2139, April 1997. [5] Gray, J., Reuter, A., Transaction Processing: Concepts and Techniques, Morgan Kaufmann Publishers, San Francisco, California, 1993. [6] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [7] Crocker, D., Overrell, P., "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [8] Aboba, B., and M. Beadles, "The Network Access Identifier", RFC 2486, January 1999. [9] McCloghrie, K., Heinanen, J., Greene, W., Prasad, A., "Accounting Information for ATM Networks", RFC 2512, February 1999. [10] McCloghrie, K., Heinanen, J., Greene, W., Prasad, A., "Managed Objects for Controlling the Collection and Storage of Accounting Information for Connection-Oriented Networks", RFC 2513, February 1999. [11] Aboba, B., Lidyard, D., "The Accounting Data Interchange Format (ADIF)", Internet draft (work in progress), draft-ietf-roamops- actng-05.txt, November 1998. [12] Fajman, R., "An Extensible Message Format for Message Disposition Notifications", RFC 2298, March 1998. [13] Elkins, M., "MIME Security with Pretty Good Privacy (PGP)", RFC 2015, October 1996. Aboba & Arkko Informational [Page 30]
INTERNET-DRAFT Accounting Management 8 June 1999 [14] Vaudreuil, G., "The Multipart/Report Content Type for the Reporting of Mail System Administrative Messages", RFC 1892, January 1996. [15] Galvin, J., et al. "Security Multiparts for MIME: Multi- part/Signed and Multipart/Encrypted", RFC 1847, October 1995. [16] Crocker, D., "MIME Encapsulation of EDI Objects", RFC 1767, March 1995. [17] Shih, C., Jansson, M., Drummond,R., "MIME-based Secure EDI", Internet draft (work in progress), draft-ietf-ediint- as1-09.txt, December 1998. [18] Shih, C., Jansson, M., Drummond, R., Yarbrough, L. "Requirements for Inter-operable Internet EDI", Internet draft (work in progress), draft-ietf-ediint-req-06.txt, December 1998. [19] Borenstein, N., Freed, N, "MIME (Multipurpose Internet Mail Extensions) Part One: Mechanisms for Specifying and Describing the Format of Internet Message Bodies", RFC 1521, December 1993. [20] Joffe, N., Wing, D., Masinter, L., "SMTP Service Extension for Immediate Delivery", Internet draft (work in progress), draft-ietf- fax-smtp-session-04.txt, August 1998. [21] Johnson, H. T., Kaplan, R. S., Relevance Lost: The Rise and Fall of Management Accounting, Harvard Business School Press, Boston, Massachusetts, 1987. [22] Horngren, C. T., Foster, G., Cost Accounting: A Managerial Emphasis. Prentice Hall, Englewood Cliffs, New Jersey, 1991. [23] Kaplan, R. S., Atkinson, Anthony A., Advanced Management Accounting, Prentice Hall, Englewood Cliffs, New Jersey, 1989. [24] Cooper, R., Kaplan, R. S., The Design of Cost Management Systems. Prentice Hall, Englewood Cliffs, New Jersey, 1991. [25] Rigney, C., Willens, S., Calhoun, P., "RADIUS Extensions", draft- ietf-radius-ext-03.txt, Internet Draft (work in progress), January 1999. [26] Carrel, D., Grant, L., "The TACACS+ Protocol Version 1.78", Internet draft (work in progress), draft-grant-tacacs-02.txt, January 1997. [27] Harrington, D., Presuhn, R., and B. Wijnen, "An Architecture for Describing SNMP Management Frameworks", RFC 2571, April 1999. Aboba & Arkko Informational [Page 31]
INTERNET-DRAFT Accounting Management 8 June 1999 [28] Rose, M., and K. McCloghrie, "Structure and Identification of Management Information for TCP/IP-based Internets", RFC 1155, May 1990. [29] Rose, M., and K. McCloghrie, "Concise MIB Definitions", RFC 1212, March 1991. [30] M. Rose, "A Convention for Defining Traps for use with the SNMP", RFC 1215, March 1991. [31] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Structure of Management Information for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1902, January 1996. [32] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Textual Conventions for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1903, January 1996. [33] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Conformance Statements for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1904, January 1996. [34] Case, J., Fedor, M., Schoffstall, M., and J. Davin, "Simple Network Management Protocol", RFC 1157, May 1990. [35] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901, January 1996. [36] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1906, January 1996. [37] Case, J., Harrington D., Presuhn R., and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", RFC 2572, April 1999. [38] Blumenthal, U., and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", RFC 2574, April 1999. [39] Levi, D., Meyer, P., and B. Stewart, "SNMPv3 Applications", RFC 2573, April 1999. [40] Wijnen, B., Presuhn, R., and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", RFC 2575, April 1999. Aboba & Arkko Informational [Page 32]
INTERNET-DRAFT Accounting Management 8 June 1999 [41] Case, J., McCloghrie, K., Rose, M., and S. Waldbusser, "Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1905, January 1996. [42] Rose, M.T., The Simple Book, Second Edition, Prentice Hall, Upper Saddle River, NJ, 1996. [43] Stewart, B., "Bulk File MIB", Internet draft (work in progress), draft-stewart-bulk-file-mib-00.txt, November 1998. [44] Stewart, B., "FTP Client MIB", Internet draft (work in progress), draft-stewart-ftp-client-mib-00.txt, November 1998. [45] Brownlee, N., "Accounting Attributes and Record Formats", Internet draft (work in progress), draft-brownlee-accounting- attributes-00.txt, May 1999. 11. Author's Addresses Bernard Aboba Microsoft Corporation One Microsoft Way Redmond, WA 98052 Phone: 425-936-6605 EMail: bernarda@microsoft.com Jari Arkko Oy LM Ericsson Ab 02420 Jorvas Finland Phone: +358 40 5079256 EMail: Jari.Arkko@ericsson.com 12. Full Copyright Statement Copyright (C) The Internet Society (1999). 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 implmentation 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, Aboba & Arkko Informational [Page 33]
INTERNET-DRAFT Accounting Management 8 June 1999 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." 13. Expiration Date This memo is filed as <draft-aboba-acct-01.txt>, and expires December 1, 1999. Aboba & Arkko Informational [Page 34]
