Contents Telektronikk - Telenor

vision of suitable information on 1) the
service as actually provided, 2) the QoS
as actually provided, and 3) the cost
incurred as related to the service and
QoS. Concerning QoS characteristics, the
following generic QoS characteristics are
defined:
- Time delay represents the difference in
time between two related events. The
time delay characteristic is quantified
in any units of time such as seconds,
milliseconds, etc.
- Time variability represents the variability
of a time or a time period. It
relates to the dispersion or jitter that
can be tolerated when time periods are
involved.
- Time window represents specific
period of time. It is a bounded time
interval which is defined by a starting
time and a time delay, by a starting and
an end time or by a time delay and an
end time.
- Capacity represents the amount of service
that can be provided in a specified
period of time.
- Accuracy represents the correctness of
an event, a set of events or a condition.
Accuracy is a QoS characteristic of
concern to the user, for whom this
characteristic refers to the user information
only.
- Protection represents the security
afforded to a resource or to information.
Protection is quantified as a probability
of failure of the protection.
- Cost represents a means of assigning
value to an object. Cost is measured in
terms of currency/unit.
- Priority represents the importance of
an object or the urgency assigned to an
event.
- Availability represents the proportion
of time when satisfactory service is
available.
- Reliability represents the probability
that accuracy will remain above a defined
requirement (i.e. that failures will
not occur).
- Coherence is the QoS characteristic
that represents the degree of correlation
between two or more objects
(events, actions or information).
3.2 The model of QoS
The purpose of the model of QoS for OSI
is to define the basic concepts necessary
for the description of QoS as it applies to
(N)-QoSrequirements
(1)
(N)-service-user
(N)-QoSrequirements
(4)
open systems. Figure 3.2 illustrates the
external flow of QoS requirements in a
confirmed (N)-service-facility. The
model of QoS recognises two types of
entities performing functions related to
the operation and management of QoS:
- layer QoS entities
- system QoS entities.
This is the same classification as used in
the ISO recommendations for specification
of OSI Management in the Recommendations
ISO 9595-96, 10165:1-4 and
10040. Layer QoS entities are associated
with the operation of a particular (N)subsystem,
and system QoS entities have
a system-wide role.
The layer QoS entities comprise: the (N)service
user, the (N)-policy-control-function
((N)-PCF), the (N)-QoS-control
function ((N)-QCF), the (N)-protocolentity
((N)-PE) and the (N-1)-serviceprovider.
Figure 3.3 illustrates the total
flow related to outgoing (N)-QoS-requirements.
The (N)-PCF receives the
(N)-QoS requirements submitted by the
(N)-service-user and applies specific
policies defined for the (N)-subsystem.
Examples are policies related to time
(N)-QoSrequirements
(3)
(N)-service-provider
(N)-service-user
(N)-QoSrequirements
(2)
Figure 3.2 Flow of QoS requirements in a confirmed (N)-service facility (from [27])
(N)-QoSrequirements
(N)-PCF
(N)-QoSrequirements
(N)-serviceprovider
(N)-service-user
(N)-QCF
(N-1)-service-provider
critical communications. (N)-QCF will
decide if the QoS requirements can be
met by the operation of an existing (N)-
PE. If so, such an (N)-PE is selected, otherwise
the call is rejected. The QoS
requirements can be modified before
sending them to the (N)-PE. The (N)-PE
can also reject the received QoS requirements.
In order to perform its function
the (N)-QCF may also need to access
information provided by the system QoS
entities.
The system QoS entities comprise: the
system policy control function (SPCF),
the system QoS control function (SQCF),
the system management agent (SMA),
the system management manager (SMM)
and the resource manager (RM). These
system entities are primarily concerned
with management functions, and the set
of system and layer QoS entities described
constitutes a functional decomposition
of an open system for the purpose of
describing QoS management. In [27]
some figures illustrating the relationship
between the layer and system QoS entities
are given. Figure 3.4 illustrates the
relationship between the layer and the
system entities.
(N)-QoSrequirements
Figure 3.3 Outgoing flow of QoS requirements (from [27])
(N-1)-QoSrequirements
(N)-PE
QoS-related
protocol
elements
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