WestSees, issue 5, July 2001:
A Generic Accounting Framework
Issue 5
July 2001
by Arthur de Jong
westsees@west.nl
Arthur de Jong is a software engineer at West
Consulting. He has a degree in computer science from Delft University of
Technology.
Accounting is the act of collecting and transporting information on
resource usage of electronic services. Accounting information is
transported to an accounting server that processes the information for
billing purposes.
There is an enormous growth in the use and availability of electronic
services and in the demand that this places on processing of usage
information. An increasing number of organisations are involved in the
delivery of a single service to a customer. This places demands in terms of
a common format in the exchange of accounting information.
Because agreeing on a common format for the exchange of all accounting
information between different organisations for different classes of
services is problematic, there is a need for a generic method for
exchanging accounting information.
Overview
Accounting addresses the collecting of information on resource usage of
supplied electronic services for the purpose of capacity and trend
analysis, cost allocation, auditing and billing.
When offering a service it is important to know how the resources that are
needed for the service are used on a per-user basis. This information is
generally needed to prepare bills for customers but also necessary for
planning purposes. If there is a need to track user access and to audit
service usage it is also important to have good information. Accounting can
also be used to internally distribute costs of a shared resource or
facility. These different applications of accounting data put different
requirements on the accounting process.
Services are provided by service elements. Examples of service elements are
Network Access Servers (dail-in boxes), voice and fax gateways, but also
web servers and routers provide services that produce usage data. The
service elements produce service dependant information on the usage of the
provided service. An accounting solution could be used for transport and
processing of this data. Accounting information would generally contain
some reference to the client who uses the service and a measure of the
different resources that were used in providing the service.
Each service provided by a service element to a client constitutes a
session, with the beginning of the session defined as the point where
service is first provided and the end of the session defined as the point
where service ended. An example of this would be the use of a dial-in
connection where the session would begin when the user dials in and end
when the user hangs up.
Accounting data that is produced in service elements will need to be
transported to an accounting server for storage and processing. The
accounting server can generate billing information or forward the data to a
specific billing solution.
The accounting data is transported in accounting messages using an
accounting protocol. The accounting protocol defines the format and type of
messages that can be sent back and forth between service element and
accounting server.
For the transport of accounting data a lot of protocols are available.
Almost every basic service has its own protocol. For some common services
several protocols are available. These protocols are rarely compatible with
each other and are mostly only usable for one particular service.
To be able to use the different available accounting protocols and to
provide a solution where future protocols can be easily integrated, a
generic accounting framework has been designed. The framework provides the
application with the services of a generic accounting protocol. Different
accounting protocols can be integrated into the framework and can be used
concurrently.
Accounting protocols are generally divided in a transport protocol, a
record format and a collection of messages. The transport protocol defines
the way the messages are sent across the network. Examples of transport
protocols are TCP, HTTP, SNMP, etc. The record format defines the way the
messages are coded into bits. ASCII, ASN.1 with BER, MIME and XML are
examples of record formats. Aside from the formatting and transport of the
messages an accounting protocol defines which messages and in what order
these messages are interchanged between the different network elements.
An accounting message consists of a message type and a collection of
attributes. These attributes contain the actual accounting information that
is transferred and the message type specifies the kind of message. Messages
can be transfers of accounting information (accounting request),
confirmation of received accounting information (accounting reply),
requests to send accounting data (accounting poll) or indications that
accounting data is ready to be sent (accounting indication).
The clear decomposition of an accounting protocol into a transport
protocol, a record format and a collection of messages provides a way to
combine different parts of different protocols so that a protocol solution
can be chosen to meet specific requirements.
Not all existing accounting protocols support sending of all types of
messages as described above and some protocols do not make a clear
distinction between record format and transport protocol. If the protocol
fits the above model, integration into the framework is straightforward.
Otherwise the protocol may require more effort to integrate into the
framework. If e.g. not all message types are supported by the protocol, the
protocol can still be used, except for the functionality requiring those
message types.
The design of the framework is based on the separation of transport, record
format and exchange of messages. At the base of the design is the
AAAUnit which combines transport protocol and record format into a
generic structure for sending and receiving accounting messages.
Outgoing messages are encoded with a given record format and sent out with
a transport protocol. If no explicit format or protocol is specified a
default will be used. Record formats and transport protocols will have to
be registered with the AAAUnit before they can be used.
Incoming connections with streams of messages or single messages received
by a transport protocol will be decoded by the AAAUnit by finding
the correct record format. After decoding the message will be passed to a
registered message handler. All registered handlers will be tried in order
until a message handler indicates the message was handled.
The AAAUnit provides a generic method of exchanging messages. To
use the unit in an accounting environment structures for sending and
handling of incoming messages need to be defined.
For this purpose an
AccountingSender and an AccountingHandler are defined.
An AccountingSender receives accounting information from the
calling application and translates this in necessary accounting messages.
The messages sent (accounting request, accounting indication) depend upon
the chosen model for sending. The AccountingHandler also handles
incoming polling requests, incoming replies to previously transmitted
accounting information; it also has a fail over mechanism with which other
accounting servers can be reached.
The AccountingHandler handles incoming accounting messages and
generates appropriate replies. The AccountingHandler can also poll
a list of clients with a regular interval. Incoming accounting indication
messages are handled by polling the sending host within a certain interval.
The AccountingSender in combination with the AAAUnit can
be used on a service element to provide the accounting functionality needed
to transport accounting information to an accounting server. The
AccountingHandler in combination with the AAAUnit can be
used to process incoming accounting information on an accounting server.
The described framework has been implemented in Java and tested in a
simulated environment. A number of protocols have been implemented mainly
for testing purposes.
With the design and implementation of the generic
accounting framework it is possible to provide accounting functionality to
service elements and accounting servers in an extensible way. Accounting
protocols can be added dynamically without changing the framework and
functionality can be easily modified and extended.
The AAAUnit of the framework can also be used in other message
exchanging environments like authentication and authorisation.
The
framework can also be used as a translating proxy between different
accounting systems that use different accounting protocols.
The defined generic accounting framework provides an accounting solution
that is independent of the underlying accounting protocol.
This project was part of the graduation project of Arthur de Jong at the
Delft University of Technology
carried out at
West Consulting B.V.
More information on this project can be found at
http://www.west.nl/project/aaa/
(primarily in Dutch).
Copyright © 2001 West Consulting BV. All rights reserved
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