Contents Telektronikk - Telenor

2 Generic concepts
2.1 Quality of service (QoS)
A service is the behaviour of some functional
capability provided by a service
provider to a service user (Figure 2.1).
The service is defined by service primitives,
and these service primitives carry
service parameters. Within the context of
ISO/OSI, a service is related to a specific
layer, and an (N)-service is the service
offered to the (N+1)-layer. The (N)-service
is the result of the functionality of
the (N)-layer-entity and the (N-1)-service.
An (N)-service is offered at an (N)service
access point. ITU defines teleservices
and bearer services. A teleservice
is a service that the user gets from the
user terminal, while a bearer service is a
service offered at some interface between
the user and the network. The ITU services
represent OSI (N)-services at specific
(N)-service access points.
ISO/OSI defines Quality of service
(QoS) as “a set of qualities related to the
provision of an (N)-service, as perceived
by an (N)-service-user”. QoS is defined
by ITU as “the collective effect of service
performance which determine the degree
of satisfaction of the user of the service”.
The relative frequency of specific events
within a service is used as a QoS measure.
These specific events are used as
quality criteria for the proper service
functioning.
The ISO definitions are found within the
OSI QoS Framework [27]. The ITU definitions
are found in E.800 “Quality of
Service and Dependability Vocabulary”
[17] and in I.350 from the series of ISDN
recommendations [22]. In addition to the
service concept, ITU also has the concept
of network performance (NP) defined as
“the ability of a network or network portion
to provide the functions related to
communication between users”.
The concept traffic performance is often
used in relationship with or instead of
QoS. QoS is directly related to the use of
common traffic resources. Examples of
traffic resources are: nodes, transmission
capacity, transmission links, routes, logical
channels, buffers, windows, and also
processing resources such as CPUs,
buses and interface-circuits within nodes
and end-systems. So the quantitative
measure of QoS is directly related to the
utilisation of the resources involved in
providing the service, i.e. the traffic on
these resources. So, traffic performance
and QoS are two strongly related concepts.
A QoS service is here defined as the
QoS-related aspects of a service relationship.
While a service comprises the total
functionality of some capability, the
QoS-service only comprises the aspects
of a service that have meaning for the
definition of the QoS. The QoS-service
defines the nature of the QoS parameters
carried on the service primitives. The
QoS-service is relevant between adjacent
layers, but is also relevant for general
client-server relationships.
2.2 QoS architecture
The functional architecture of a telecommunication
service providing system is
defined as the total set of functional elements
and the dynamic relationship between
these functional elements. This
architecture has an operational and a
management part. The operational architecture
defines the primary functionality
related to the real-time handling of a call,
while the management architecture defines
the additional functionality needed
for the administration of this operational
functionality.
A QoS architecture is a view of a functional
architecture, considering the traffic-resource-related
aspects, i.e. the traffic
resources and the functionality for the
Functional architecture
Management
architecture
QoS Architecture
Management
architecture
Service
relationship
Operational
architecture
Operational
architecture
Service
user
Service
provider
• Service
• QoS
Service primitives,
service parameters
Figure 2.1 A generic service relationship
administration of these resources. Faulthandling
functionality will be a part of
the QoS architecture. This because of the
tight connection between fault-handling
and traffic resources. A QoS architecture
will also have an operational and a management
part, denoted as the operational
and management QoS architecture,
respectively. The relationship between
the functional architecture and the QoS
architecture is illustrated in Figure 2.2.
QoS is a characteristic of how well the
service is performed. But a system must
also have the ability to provide a certain
QoS. This ability can depend very much
on the system architecture and accordingly
on the principles for the realisation
of system functionality. The QoS archi-
User
Provider
QoS View
User
Provider
• Service
• QoS
Service primitives
service parameters
• Service
• QoS
Service primitives
service parameters
Figure 2.2 The relationship between the functional architecture and the QoS architecture
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