accounting
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...
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 ...
... accounting systems.
Since accounting applications do not have uniform security and
reliability ...
... 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 ...
... 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 ...
... tools as well as the
state of the art in accounting protocol design. A companion
document, RFC 2924, reviews the state ...
... document, RFC 2924, reviews the state of the art in accounting
attributes and record formats.
...
... This document frequently uses the following terms:
Accounting
The collection of resource consumption data for the
purposes of capacity and trend analysis, cost allocation,
...
... 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
...
... Archival accounting
In archival accounting, the goal is to collect all
accounting data, to reconstruct missing entries as best as
...
... 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
...
... 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.
...
... typically a given.
Interim accounting
Interim accounting provides a snapshot of usage during a
...
... Interim accounting
Interim accounting provides a snapshot of usage during a
user's session. This may be useful in the event of a
...
... session summary packet or
session record. Interim accounting records can always be
summarized without the loss of information. Note that
interim accounting ...
... 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
...
... session record represents a summary of the resource
consumption of a user over the entire session. Accounting
gateways creating the session ...
... gateways creating the session record may do so by
processing interim accounting events or accounting events
from several devices serving the same user.
...
... session record may do so by
processing interim accounting events or accounting events
from several devices serving the same user.
...
... from several devices serving the same user.
Accounting Protocol
A protocol used to convey data for accounting purposes.
...
... accounting
Intra-domain accounting involves the collection of
information on resource usage within an administrative
domain, for use within that domain ...
... intra-domain
accounting, accounting packets and session records
typically do not cross administrative boundaries ...
... accounting
Inter-domain accounting involves the collection of
information on resource usage within an administrative
domain, for use within another administrative domain ...
... inter-domain accounting, accounting packets and session
records will typically cross administrative boundaries ...
... accounting
Real-time accounting involves the processing of information
on resource usage within a defined time window. Time
constraints ...
... Accounting server
The accounting server receives accounting data from devices
and translates it into session ...
... Accounting server
The accounting server receives accounting data from devices
and translates it into session records. The accounting ...
... accounting data from devices
and translates it into session records. The accounting
server may also take responsibility for the routing of
...
... Accounting management architecture ...
... management architecture involves interactions between
network devices, accounting servers, and billing servers. The
network device collects resource consumption data in the form of
...
... 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 ...
... 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 ...
... 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.
...
... session records.
The accounting server then processes the accounting data received
from the network ...
...
The accounting server then processes the accounting data received
from the network device. This processing may include summarization
...
... from the network device. This processing may include summarization
of interim accounting information, elimination of duplicate data, or
generation of session records.
...
... session records.
The processed accounting data is then submitted to a billing server,
which typically handles rating and invoice generation, but may also
...
... 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 ...
... 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.
...
... required to accomplish the transfer.
One of the functions of the accounting server is to distinguish
between inter and intra-domain accounting ...
... accounting server is to distinguish
between inter and intra-domain accounting events and to route them
appropriately. For session ...
... session record is
treated as an intra-domain accounting event. Otherwise, it is
treated as an inter-domain accounting ...
... accounting event. Otherwise, it is
treated as an inter-domain accounting event.
Intra-domain ...
...
Intra-domain accounting events are typically routed to the local
billing server, while inter-domain accounting ...
... 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 ...
... inter-domain accounting events will be routed
to accounting servers operating within other administrative domains.
While it is not required that session ...
... 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.
...
... 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
...
... proxy forwarder, which may then either convert the
accounting packets to session records, or forward the accounting
...
... accounting packets to session records, or forward the accounting
packets to another domain. In either case, domain ...
... destination.
Where the accounting proxy is not trusted, it may be difficult to
verify that the proxy ...
... proxy is issuing correct session records based on the
accounting messages it receives, since the original accounting
messages typically are not forwarded along with the session ...
... session records based on the
accounting messages it receives, since the original accounting
messages typically are not forwarded along with the session records.
...
... trust is an issue, the proxy typically forwards the
accounting packets themselves. Assuming that the accounting protocol
supports data object ...
... proxy typically forwards the
accounting packets themselves. Assuming that the accounting protocol
supports data object security ...
... packet contents.
The diagram below illustrates the accounting management architecture:
...
... +------------+
|
Accounting |
Protocol |
|
...
... | Acctg. |<----------------------------->| Acctg. |
|Proxy/Server| or accounting protocol | Server |
| | | |
+------------+ +------------+
...
... Accounting management objectives ...
...
Accounting Management involves the collection of resource consumption
data for the purposes of capacity and trend analysis, cost
...
...
When accounting data is used for billing purposes, the requirements
depend on whether the billing process is usage-sensitive or not.
...
...
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 this would also affect
other tasks such as trend analysis or auditing, so that such
...
... billing process may need to conform to financial reporting and legal
requirements, and therefore an archival accounting approach may be
needed.
...
... systems that are designed to detect unusual activity. While
efficiency concerns might otherwise dictate batched transmission of
accounting data, where there is a risk of fraud, financial exposure
increases with processing delay. Thus it may be advisable to
transmit each event individually to minimize batch size, or even to
...
... time window in order to limit exposure.
Since in usage-sensitive systems, accounting data translates into
revenue, the security and reliability ...
... Application-layer acknowledgments are also often required so as to
guard against accounting server failures.
...
... 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 the correctness of an invoice
...
... To permit a credible audit, the auditing data collection process must
be at least as reliable as the accounting process being used by the
entity that is being audited. Similarly, security policies ...
... invoice. Due to financial and legal requirements,
archival accounting practices are frequently required in this
application.
...
... security as are billing applications. Due to
financial and legal requirements, archival accounting practices are
frequently required in this application.
...
... management has focused on
intra-domain accounting applications. However, with the increasing
deployment of services ...
... QoS, applications requiring inter-domain
accounting are becoming increasingly common.
Inter-domain ...
... Inter-domain accounting differs from intra-domain accounting in
several important ways. Intra-domain accounting ...
... accounting in
several important ways. Intra-domain accounting involves the
collection of information on resource consumption within an
administrative domain ...
... intra-domain
accounting, accounting packets and session records typically do not
cross administrative boundaries ...
... administrative boundaries. As a result, intra-domain
accounting applications typically experience low 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,
...
... administrative domain. In inter-domain
accounting, accounting packets and session records will typically
...
... inter-domain
accounting, accounting packets and session records will typically
cross administrative boundaries ...
... administrative boundaries. As a result, inter-domain
accounting applications may experience substantial packet loss. In
addition, the entities involved in the transfers cannot be assumed to
...
...
Since inter-domain accounting applications involve transfers of
accounting data between domains ...
... inter-domain accounting applications involve transfers of
accounting data between domains, additional security measures may be
...
... data object integrity. In inter-domain
accounting each involved party also typically requires a copy of each
accounting event for invoice ...
... accounting each involved party also typically requires a copy of each
accounting event for invoice generation and auditing.
...
... Accounting record production ...
...
Typically, a single accounting record is produced per session, or in
some cases, a set of interim records which can be summarized in a
...
... more sophisticated approach is required.
It is necessary to generate several accounting records from a single
session when pricing changes during a session ...
... session could be re-authorized with improved QoS.
This would require production of accounting records at both QoS
levels.
...
... session. A session identifier needs to be present
in the records to permit accounting systems to tie the records
together.
...
... future systems are being designed that enable the home domain to
control the generation of accounting records. This is of importance
in inter-domain ...
... importance
in inter-domain accounting or when network devices do not have tariff
information. The centralized control of accounting ...
... accounting or when network devices do not have tariff
information. The centralized control of accounting record production
can be realized, for instance, by having authorization servers
...
... require re-authorization at certain times and requiring the
production of accounting records upon each re-authorization.
...
...
In conclusion, in some cases it is necessary to produce multiple
accounting records from a single session. It must be possible to do
this without requiring the user to start ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Archival | Archival |
| Usage | accounting | accounting |
| Sensitive | Integrity ...
... | | Archival | Archival |
| Usage | accounting | accounting |
| Sensitive | Integrity, | Integrity ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Archival | Archival |
| Time | accounting | accounting |
| Sensitive | Integrity ...
... | | Archival | Archival |
| Time | accounting | accounting |
| Sensitive | Integrity, | Integrity ...
... 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 ...
... accounting management systems be scalable and reliable. This section
discusses the resources consumed by accounting management systems as
well as the scalability ...
...
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
...
... frequently mandated, due to financial and legal requirements. Since
in such situations loss of accounting data can translate to revenue
loss, there is incentive to engineer a high degree of fault
resilience. Faults which may be encountered include:
...
... Device reboots
To date, much of the debate on accounting reliability has focused on
resilience against packet loss ...
... resilience against packet loss is only one aspect of meeting
archival accounting requirements.
As noted in [18 ...
... network
partition, accounting server failures or device reboots. What does
provide resilience against these faults is non-volatile storage.
...
... importance of non-volatile storage in design of reliable
accounting systems cannot be over-emphasized. Without non-volatile
storage, event-driven systems will lose data once the transmission
timeout has been exceeded, and batching designs will experience data
...
... non-volatile
storage, event-driven systems will lose data once the transmission
timeout has been exceeded, and batching designs will experience data
loss once the internal memory used for accounting data storage has
been exceeded. Via use of non-volatile storage, and internally
...
... It may even be argued that non-volatile storage is more important to
accounting reliability than network connectivity, since for many
...
... reliability than network connectivity, since for many
years reliable accounting systems were implemented based solely on
physical storage, without any network ...
... Interim accounting ...
... TACACS+.
While interim accounting can provide resilience against packet loss,
server failures, short-duration network ...
... server failures, short-duration network failures, or device reboot,
its applicability is limited. Transmission of interim accounting
data over the wire should not be thought of as a mainstream
reliability ...
... Internet is due to congestion, sending
interim accounting data over the wire can make the problem worse by
increasing bandwidth usage. Therefore on-the-wire interim accounting ...
... accounting data over the wire can make the problem worse by
increasing bandwidth usage. Therefore on-the-wire interim accounting
is best restricted to high-value accounting data such as information
...
... bandwidth usage. Therefore on-the-wire interim accounting
is best restricted to high-value accounting data such as information
on long-lived sessions. To protect against loss of data ...
... ensures that most sessions will not result in generation of interim
accounting events and the additional bandwidth consumed by interim
accounting ...
... accounting events and the additional bandwidth consumed by interim
accounting will be limited. However, as the interim accounting
interval decreases toward the average session ...
... bandwidth consumed by interim
accounting will be limited. However, as the interim accounting
interval decreases toward the average session time, the additional
...
... session time, the additional
bandwidth consumed by interim accounting increases markedly, and as a
result, the interval must be set with caution.
...
... 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 ...
... 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 in memory, thereby worsening the buffer ...
... Where non-volatile storage is available, this can be used to store
interim accounting data. Stored interim events are then replaced by
updated interim events or by session data when the session ...
... avoids interim data being transmitted over the wire except in the
case of a device reboot. When a device reboots, internally stored
interim records are transferred to the accounting server.
...
... introduce scalability problems that cannot be controlled using the
techniques available in interim accounting.
For example, in the case of interim records kept in non-volatile
storage ...
... interim updates are sent over the wire, it is possible to control
bandwidth usage by adjusting the interim accounting interval.
These measures are not applicable where multiple session ...
... send all of the related records together in a batch when the session
completes. It may also be desirable to shape the accounting traffic
flow so as to reduce the peak bandwidth consumption. This can be
...
... accomplished by introduction of a randomized delay interval. If the
home domain can also control the generation of multiple accounting
records, the estimation of the worst-case processing requirements can
...
... As packet loss is a fact of life on the Internet, accounting
protocols dealing with session data need to be resilient against
packet loss ...
... packet loss. This is particularly important in inter-domain
accounting, where packets often pass through Network Access Points
(NAPs) where packet loss ...
... SCTP [26]. On-the-wire
interim accounting provides only limited benefits in mitigating the
effects of packet loss.
...
... UDP-based transport is frequently used in accounting applications.
However, this is not appropriate in all cases. Where accounting data
...
... transport is frequently used in accounting applications.
However, this is not appropriate in all cases. Where accounting data
will not fit within a single UDP packet without fragmentation ...
... Timeout behavior
Accounting reliability can be influenced by how the data is modeled.
For example, it is almost always preferable to use cumulative
...
... reliability can be influenced by how the data is modeled.
For example, it is almost always preferable to use cumulative
variables rather than expressing accounting data in terms of a change
from a previous data item. With cumulative data, the current state
...
... retransmissions will
not typically occur within the period in which acknowledgments may be
expected to arrive. Accounting bandwidth may be significant in some
circumstances, so that the added traffic ...
...
Congestion control in accounting data transfer is a somewhat
controversial issue. Since accounting ...
... accounting data transfer is a somewhat
controversial issue. Since accounting traffic is often considered
mission-critical ...
... congestion. Moreover, without non-volatile storage,
congestive back-off in accounting applications can result in data
loss due to buffer exhaustion.
...
... buffer exhaustion.
However, it can also be argued that in modern accounting
implementations, it is possible to implement congestion control while
...
... 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
...
... considerable leeway is available to the network administrator in
controlling the treatment of accounting packets and hard coding
inelastic behavior is unnecessary. Typically, systems implementing
non-volatile storage ...
... inelastic behavior is unnecessary. Typically, systems implementing
non-volatile storage allow for backlogged accounting data to be
placed in non-volatile storage pending transmission, so that buffer ...
... UDP is not really a transport protocol, UDP-based accounting
protocols such as [4] often do not prescribe timeout behavior. Thus
implementations may exhibit widely different behavior. For example,
...
... 4] often do not prescribe timeout behavior. Thus
implementations may exhibit widely different behavior. For example,
one implementation may drop accounting data after three constant
duration retries to the same server, while another may implement
exponential back-off to a given server, then switch ...
... non-volatile storage. The practical
difference between these approaches is substantial; the former
approach will not satisfy archival accounting requirements while the
latter may. More predictable behavior can be achieved via use of
SCTP ...
... Accounting server failover ...
...
In the event of a failure of the primary accounting server, it is
desirable for the device to failover to a secondary server.
Providing one or more secondary servers can remove ...
... Providing one or more secondary servers can remove much of the risk
of accounting server failure, and as a result use of secondary
servers has become commonplace.
...
... TCP, it is possible for the device to maintain
connections to both the primary and secondary accounting servers,
using the secondary connection after expiration of a timer ...
... connection. Alternatively, it is possible to open a
connection to the secondary accounting server after a timeout or loss
of the primary connection, or on expiration of a timer ...
... connection, or on expiration of a timer. Thus,
accounting protocols based on TCP are capable of responding more
rapidly to connectivity failures than TCP ...
... SCTP, it is possible to control transport layer timeout
behavior, and therefore it is not necessary for the accounting
application to maintain its own timers. SCTP ...
... round-trip-time estimation, slow start
and congestive back-off. Thus the accounting protocol designer
utilizing UDP often is lead to re-inventing techniques already
...
... With any transport it is possible for the primary and secondary
accounting servers to receive duplicate packets, so support for
duplicate elimination is required. Since accounting server failures
...
... accounting servers to receive duplicate packets, so support for
duplicate elimination is required. Since accounting server failures
can result in data accumulation on accounting clients ...
... duplicate elimination is required. Since accounting server failures
can result in data accumulation on accounting clients, use of non-
volatile storage ...
... volatile storage can ensure against data loss due to transmission
timeouts or buffer exhaustion. On-the-wire interim accounting
provides only limited benefits in mitigating the effects of
accounting ...
... accounting
provides only limited benefits in mitigating the effects of
accounting server failures.
...
...
It is possible for the accounting server to experience partial
failures. For example, a failure in the database back end could
...
... failures. For example, a failure in the database back end could
leave the accounting retrieval process or thread operable while the
process or thread responsible for storing the data is non-functional.
Similarly, it is possible for the accounting ...
... accounting retrieval process or thread operable while the
process or thread responsible for storing the data is non-functional.
Similarly, it is possible for the accounting application to run out
of disk space, making it unable to continue storing incoming session
...
... responsibility for the data.
For example, an accounting server may receive data from the transport
layer but be incapable of storing it data due to a back end database
...
... 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
...
... client. In the event of partial
connectivity loss, it may not be possible to reach the primary
accounting server, in which case switch over to the secondary
accounting ...
... accounting server, in which case switch over to the secondary
accounting server is necessary. In the event of a network partition,
...
... network partition,
it may be necessary to store accounting events in device memory or
non-volatile storage until connectivity can be re-established.
...
... 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 ...
...
As with accounting server failures, on-the-wire interim accounting
provides only limited benefits in mitigating the effects of network
...
... consumption. To guard against loss of these high-value sessions,
interim accounting data is typically transmitted over the wire. When
interim accounting in-place is combined with non-volatile storage ...
... interim accounting data is typically transmitted over the wire. When
interim accounting in-place is combined with non-volatile storage it
becomes possible to guard against data loss in much shorter sessions ...
... 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 ...
... Accounting proxies ...
... In order to maintain high reliability, it is important that
accounting proxies pass through transport and application layer ...
... transport and application layer
acknowledgments and do not store and forward accounting packets.
This enables the end-systems to control re-transmission behavior and
utilize techniques such as non-volatile storage ...
... ACK to
the device without receiving one from the accounting server fool the
device into thinking that the accounting request had been accepted by
...
... receiving one from the accounting server fool the
device into thinking that the accounting request had been accepted by
the accounting server when this is not the case. As a result, the
...
... device into thinking that the accounting request had been accepted by
the accounting server when this is not the case. As a result, the
device can delete the accounting ...
... accounting server when this is not the case. As a result, the
device can delete the accounting packet from non-volatile storage
before it has been accepted by the accounting ...
... accounting packet from non-volatile storage
before it has been accepted by the accounting server. The leaves the
accounting proxy ...
... before it has been accepted by the accounting server. The leaves the
accounting proxy responsible for delivering accounting packets. If
...
... proxy responsible for delivering accounting packets. If
the accounting proxy involves moving parts (e.g. a disk drive) while
the devices do not, overall system ...
... reliability can be reduced.
Store and forward accounting proxies only add value in situations
where the accounting ...
... accounting proxies only add value in situations
where the accounting subsystem is unreliable. For example, where
devices do not implement non-volatile storage and the accounting
protocol ...
... accounting subsystem is unreliable. For example, where
devices do not implement non-volatile storage and the accounting
protocol lacks transport and application layer reliability ...
... application layer reliability, locating
the accounting proxy (with its stable storage) close to the device
can reduce the risk of data loss.
...
... However, such systems are inherently unreliable so that they are only
appropriate for use in capacity planning or non-usage sensitive
billing applications. If archival accounting reliability is desired,
it is necessary to engineer a reliable accounting ...
... accounting reliability is desired,
it is necessary to engineer a reliable accounting system from the
start using the techniques described in this document, rather than
...
... start using the techniques described in this document, rather than
attempting to patch an inherently unreliable system by adding store
and forward accounting proxies.
...
... Well-defined timeout behavior |
| | Duplicate elimination |
| | Interim accounting* |
| | Non-volatile storage |
...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
| Accounting | Primary-secondary servers |
| server & net | Duplicate elimination |
| failures | Interim accounting ...
... Accounting | Primary-secondary servers |
| server & net | Duplicate elimination |
| failures | Interim accounting* |
| | Application layer ACK ...
... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
| Device | Interim accounting* |
| reboots | Non-volatile storage |
...
... In the process of growing to meet the needs of providers and
customers, accounting management systems consume a variety of
resources, including:
...
... management systems consume network bandwidth in
transferring 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
...
... bandwidth
consumption. As a result, it is often desirable to transfer
accounting data in batches, enabling network overhead to be spread
...
... noted in [48], compression can be enabled in the accounting protocol,
or can be done at the IP layer as described in [5 ...
... 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
...
... 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 ...
... non-volatile storage is unavailable, it may be desirable to compress
accounting data awaiting transmission.
As noted earlier, implementors ...
...
As noted earlier, implementors of interim accounting should take care
to ensure against excessive memory usage by overwriting older interim
accounting ...
... 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 ...
...
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 ...
... 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 non-volatile storage declining rapidly, network ...
... Non-volatile storage may be used to store interim or session records.
As with memory utilization, interim accounting overwrite is desirable
so as to prevent excessive storage consumption. Note that the use of
ASCII ...
...
In order to keep track of received accounting data, accounting
management systems may need to keep state ...
... 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.
...
... 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.
...
... | Memory | Compression |
| | Interim accounting overwrite |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
... | Non-volatile | Compression |
| Storage | Interim accounting overwrite |
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...
... Several data collection models are currently in use today for the
purposes of accounting data collection. These include:
...
...
In the polling model, an accounting manager will poll devices for
accounting information at regular intervals. In order to ensure
...
... In the polling model, an accounting manager will poll devices for
accounting information at regular intervals. In order to ensure
against loss of data, the polling interval will need to be shorter
...
... against 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-
...
... 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 ...
... 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 ...
... 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 ...
... 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 ...
... 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
...
... provisioning or Internet access. This is because in order to
retrieve accounting data for users within a given domain, the
Accounting ...
... accounting data for users within a given domain, the
Accounting Management station would need to periodically poll all
devices in all domains ...
... data. There are also issues with processing delay, since use of a
polling interval also implies an average processing delay of half the
polling interval. This may be too high for accounting data that
requires low processing delay. Thus the event-driven polling or the
pure event-driven approach is more appropriate for usage sensitive
...
... Per-device state is typical of polling-based network management
systems, which often also carry out accounting management functions,
since network management systems ...
...
In the event-driven model, a device will contact the accounting
server or manager when it is ready to transfer accounting data. Most
...
... 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 ...
... server or manager when it is ready to transfer accounting data. Most
event-driven accounting systems, such as those based on RADIUS
accounting ...
... accounting systems, such as those based on RADIUS
accounting, described in [4], transfer only one accounting event per
...
... accounting, described in [4], transfer only one accounting event per
packet, which is inefficient.
...
... Without non-volatile storage, a pure event-driven model typically
stores accounting events that have not yet been delivered only until
the timeout interval expires. As a result this model has the
smallest memory requirements ...
... smallest memory requirements. Once the timeout interval has expired,
the accounting event is lost, even if the device has sufficient
buffer space to continue to store it. As a result, the event-driven
...
... buffer space to continue to store it. As a result, the event-driven
model is the least reliable, since accounting data loss will occur
due to device reboots, sustained packet loss, or network ...
... network failures of
duration greater than the timeout interval. In event-driven
protocols without a "keep alive" message, accounting servers cannot
assume a device failure should no messages arrive for an extended
period. Thus, event-driven accounting ...
... accounting servers cannot
assume a device failure should no messages arrive for an extended
period. Thus, event-driven accounting systems are typically not
useful in monitoring of device health.
...
... requiring them to poll a large number of devices, most of which have
no relevant data. Since the event-driven model typically does not
support batching, it permits accounting records to be sent with low
processing delay, enabling application of fraud prevention
techniques. However, because roaming ...
... processing delay, enabling application of fraud prevention
techniques. However, because roaming accounting events are
frequently of high value, the poor reliability of this model is an
...
...
In the event-driven model with batching, a device will contact the
accounting server or manager when it is ready to transfer accounting
data. The device can contact the server when a batch of a given size
...
... In the event-driven model with batching, a device will contact the
accounting server or manager when it is ready to transfer accounting
data. The device can contact the server when a batch of a given size
has been gathered, when data of a certain type is available or after
...
... has been gathered, when data of a certain type is available or after
a minimum time period has elapsed. Such systems can transfer more
than one accounting event per packet and are thus more efficient.
An event-driven system with batching will store accounting ...
... accounting event per packet and are thus more efficient.
An event-driven system with batching will store accounting events
that have not yet been delivered up to the limits of memory. As a
result, accounting ...
... accounting events
that have not yet been delivered up to the limits of memory. As a
result, accounting data loss will occur due to device reboots, but
not due to packet loss or network ...
... keep-alive interval
and run over reliable transport, the accounting server can assume
that a failure has occurred if no messages are received within the
keep-alive ...
... algorithm, event-driven
systems with batching can deliver appropriate service to accounting
events that require low processing delay. For example, high-value
inter-domain ...
... events that require low processing delay. For example, high-value
inter-domain accounting events could be sent immediately, thus
enabling use of fraud-prevention techniques, while all other events
would be batched. However, there is a possibility that an event
...
... delay than the event-driven polling approach, since delivery of
accounting data requires fewer round-trips and events requiring low
processing delay can be accommodated if a scheduling algorithm ...
...
In the event-driven polling model an accounting manager will poll the
device for accounting data only when it receives an event. The
...
... 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 ...
... 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
...
... The event-driven polling model can be 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 ...
... 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.
...
... actually be less than that of the polling approach. Note that
processing delay in this approach is higher than in event-driven
accounting with batching since at least two round-trips are required
to deliver data: one for the event notification ...
... Review of Accounting Protocols ...
... 3]. As a result,
RADIUS accounting shares the event-driven approach of RADIUS
authentication ...
... 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 ...
... result, RADIUS accounting scales with the number of accounting events
instead of the number of devices, and accounting transfers are
...
... accounting scales with the number of accounting events
instead of the number of devices, and accounting transfers are
inefficient.
...
...
Since RADIUS accounting is based on UDP and timeout and retry
parameters are not specified, implementations vary widely in their
...
... delivery or buffer exhaustion, and others losing accounting data
after a few retries. Since RADIUS accounting ...
... accounting data
after a few retries. Since RADIUS accounting does not provide for
application-layer acknowledgments or error messages ...
... error messages, a RADIUS
Accounting-Response is equivalent to a transport-layer acknowledgment
and provides no protection against ...
... reliability, it is not possible to do simultaneous
usage control based on RADIUS accounting alone. Typically another
device data source is required, such as polling of a session MIB ...
...
RADIUS accounting implementations are vulnerable to packet loss as
well as application layer ...
... network failures and device
reboots. These deficiencies are magnified in inter-domain accounting
as is required in roaming ([1 ...
... 2]). On the other hand, the event-
driven approach of RADIUS accounting is useful where low processing
delay is required, such as credit risk management or fraud detection.
...
...
While RADIUS accounting does provide hop-by-hop authentication and
integrity protection, and IPSEC ...
... security is not supported, and thus
systems based on RADIUS accounting are not capable of being deployed
with untrusted proxies, or in situations requiring auditability, as
...
... application layer acknowledgments, and is suitable for simultaneous
usage control and handling of accounting events that require moderate
though not the lowest processing delay.
...
... security is not supported, and therefore systems based on TACACS+
accounting are not deployable in the presence of untrusted proxies.
While TACACS ...
... 41], has been widely deployed in a wide
variety of intra-domain accounting applications, typically using the
polling data collection model. Polling allows data to be collected
...
... polling data collection model. Polling allows data to be collected
on multiple accounting events simultaneously, resulting in per-device
state. Management applications ...
... or event-driven batching model. However, we are not aware of any
SNMP-based accounting implementations currently built on the use of
Informs.
...
... domains and devices is large, such as in
inter-domain accounting applications, the number of shared secrets
can get out of hand. The localized key ...
... important role, forwarding intra and inter-domain accounting events
to the correct destinations. The proxy ...
... 1]. Since 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 ...
... 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.
...
... domain-based access controls, in inter-domain
accounting, it is first necessary to identify the data subset that is
to have its access controlled. Several conceptual abstractions are
used for identifying subsets of data in SNMP ...
... contexts, and views. This section describes how this functionality
may be applied in intra and inter-domain accounting.
...
... networks or roaming associations relying on SNMP-based accounting
have generally collected data for all organizations and then sorted
the resulting session ...
... SNMP-enabled devices to notify domains that have
accounting data awaiting collection. SNMP Applications [39] defines
...
... context. The agent needs to collect
accounting data by domain and make the data accessible via distinct
contexts ...
... Domain separation is handled by using contextName to differentiate
multiple virtual tables. For example, if accounting data has been
collected on users with the bigco.com and smallco.com domains, then a
...
... collected on users with the bigco.com and smallco.com domains, then a
separate virtual instance of the accounting session record table
would exist for each domain ...
... 49].
In accounting applications, management stations often must retrieve
large tables. Latency ...
... MIB modules, it is
likely that SNMP will remain a popular accounting protocol for the
foreseeable future.
...
... SNMP-
based intra-domain accounting implementations to upgrade to SNMPv3.
Such an upgrade is virtually mandatory for inter-domain ...
...
In inter-domain accounting, the burden of managing SNMPv3 shared
secrets can be reduced via the localized key ...
...
SNMP-based accounting has limitations in terms of efficiency and
latency that may make it inappropriate for use in situations
...
...
SNMP supports separation of accounting data by domain, using either
of two general approaches with the VACM ...
... Review of 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 ...
... SMI
data types, as well as alternative protocols for transmission of
accounting data. For example, [49] describes how MIME tags ...
... Accounting management systems using SMTP for accounting transfer will
typically support batching so that message processing overhead 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 ...
... 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, accounting systems implemented using SMTP ...
... accounting records until they are transferred to the collection site.
As a result, accounting systems implemented using SMTP can be highly
efficient and scalable. Using IPSEC ...
... repudiation as described in [12]-[17]. As a result, accounting
systems utilizing SMTP for accounting ...
... accounting
systems utilizing SMTP for accounting data transfer are capable of
satisfying the most demanding security requirements ...
... FTP and HTTP have been used for
transfer of accounting data. For example, Reference [9] describes a
means for representing ASN.1 ...
... 9] describes a
means for representing ASN.1-based accounting data for storage on
archival media. Through the use of the Bulk File MIB, accounting ...
... accounting data for storage on
archival media. Through the use of the Bulk File MIB, accounting
data from an SNMP MIB can be stored in ASN.1 ...
...
Given access to sufficient non-volatile storage, accounting systems
based on record formats and transfer protocols can avoid loss of data
...
... 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 ...
...
As noted previously in this document, accounting applications vary in
their security and reliability ...
... security and reliability, since in these cases the transfer
of accounting data will lead directly to the transfer of funds.
Since accounting ...
... accounting data will lead directly to the transfer of funds.
Since accounting applications do not have uniform security and
reliability ...
... reliability requirements, it is not possible to devise a single
accounting protocol and set of security services that will meet all
needs. Rather, the goal of accounting ...
... 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 ...
... 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
...
... 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 ...
... packet loss, as well as application layer acknowledgments to provide
robustness against accounting server failures. SNMP operations with
the exception of InforRequest provide application layer ...
... McCloghrie, K., Heinanen, J., Greene, W. and A. Prasad, "Accounting Information for ATM Networks", RFC 2512prop ...
... McCloghrie, K., Heinanen, J., Greene, W., and A. Prasad, "Managed Objects for Controlling the Collection and Storage of Accounting Information for Connection-Oriented Networks", RFC 2513prop ...
... Johnson, H. T., Kaplan, R. S., Relevance Lost: The Rise and Fall of Management Accounting, Harvard Business School Press, Boston, Massachusetts, 1987. ...
... Horngren, C. T., Foster, G., Cost Accounting: A Managerial Emphasis. Prentice Hall, Englewood Cliffs, New Jersey, 1991. ...
... Kaplan, R. S., Atkinson, Anthony A., Advanced Management Accounting, Prentice Hall, Englewood Cliffs, New Jersey, 1989. ...
... Brownlee, N. and A. Blount, "Accounting Attributes and Record Formats", RFC 2924, September 2000. ...