UCL (University College London). The imple-
mented solutions have then been analysed
through experimental tests. More detail on these
can be found in [P906-7], [P906-8].
7 Charging Schemes
After considering the charging and accounting
model and architecture, the charging of both
connectivity/transport and end-user services is
discussed in this chapter. The simplest usage-
based charging scheme, which can be applied
to both connectivity/transport and end-user ser-
vices, and which considers volume in addition to
time as a measure of usage, is the scheme where
the charge is calculated by using a simple func-
tion that is linear in measurements of time and
volume. The parameters of this function, which
represent a charge per unit of time and a charge
per unit of volume, are a function of the parame-
ters of the Quality Class Specification (QCS),
namely the NPL, which contains a set of target
values (or range of values) for relevant Network
Performance Parameters (NPP) that are guaran-
teed by the network, and the traffic profile,
which describes the maximum amount of con-
forming traffic that the user can send. This will
be discussed in more detail later. The notation
used in the following subsections is given in
ingress A.
A charging schemeis an algorithm for calculat-
ing the charge for some network service2). In the
case of telecommunication services, a user’s
charge is calculated based on accounting data
that contain information regarding the resource
consumption for that user, and prices from tariff
tables published by the provider. Bearing in
mind the business model described in Section 2,
network connectivity services are offered over
the SP-NP interface. Such services involve the
transfer of bits with, possibly, some performance
guarantees, but without any knowledge of the
higher layer application that generated the traf-
fic. End-services are those offered over the user
- SP interface. Charges for such services include
both connectivity/transport level charges and
application level charges, where the latter de-
pend on the particular service (application)
offered. Basically, charging for network trans-
port service involves charges for a basic service,
while charging for end-services involves both
charges for the basic services and for value-
added services.
In general, a charge for network connectivity
services may include a subscription3)component
and a usage component. The subscription com-
ponentcan consist of a one-time site connection
fee, which is paid once when the user’s network
is connected to the provider and corresponds to
the cost of equipment and labour necessary for
connecting a customer’s network with the pro-
vider, and a rental (e.g. monthly) that is associ-
ated with facilities in the access portion (e.g.
router ports), as well as operational and mainte-
nance costs. The usage componentis associated
with resource reservation and consumption in
the backbone. It can consist of the following:- A fee for setting-up a connection (for connec-
tion-oriented services like IP telephony), that
is associated with the signalling required to
set-up the connection and the maintenance of
related state information. - A charge for consumed resources, which
depends on measures of resource usage such
as the duration (time), the volume transferred,
quality class. Such measures are captured by
charging and accounting systems and are
included in the accounting data.
Considering all parts mentioned, a customer’s
charge for network connectivity services can be
expressed as follows:(1)
where Usage_chargeiis the charge for connec-
tion i. In the simple case where duration (time)
and volume are the only measures of resource
consumption, then the usage charge can be ex-
pressed as follows:(2)
where xidescribes, in the terminology of the
QUASI-model, the NPL and the traffic profile
for connection i. The measured variables Tiand
Viare the duration and transferred volume,
respectively, for connection i. Finally, the prices
pT, pV, and pcare the price per unit of time (e.g.
per minute), the price per unit of volume (e.g.
per Mbyte), and the connection set-up fee (e.g.
per connection), respectively. The price pTcor-
responds to the amount of resources reserved,
whereas the price pVcorresponds to the actual
amount of resources used. In addition to techni-
cal considerations, expressed through the depen-
dence on xi, these prices will depend on eco-Usage_chargei=
pT(xi)Ti+pV(xi)Vi+pc(xi)Charge=
Access_charge+ Usage_chargei
i∑
2)In this section, the term “network service” is used to refer to either end-user service or network
transport service.
3)Note that this component is sometimes in literature referred to as the access fee/component.