wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

19
Quality of Service
Gabriel Diaz Orueta
Spanish University of
Distance Education, UNED
Elio San
Cristobal Ruiz
Spanish University of
Distance Education, UNED
Nuria Oliva Alonso
Spanish University of
Distance Education, UNED
Manuel Castro Gil
Spanish University of
Distance Education, UNED
19.1 Introduction..................................................................................... 19-1
19.2 Relationship with Information Security Topics......................... 19-3
19.3 Quality of Service for IP Networks..............................................19-4
Integrated Services (IntServ) Model. •. Differentiated Services
(DiffServ) Model. •. Classification and Marking. •. Queuing
and Congestion Management
19.4 Special Considerations for Managing the Quality
of Service....................................................................................... 19-11
Congestion Avoidance. •. High Availability Solutions for the Routers
References.................................................................................................. 19-14
19.1 Introduction
Nowadays, almost any industrial network uses applications based on IP networks [1]. This means that
people controlling these networks need to know at least the basics of quality of service (QoS) for IP networks.
Every device used in an industrial network is going to send and receive IP packets but, depending
on the nature of the industrial application we use in the device, the way to process the IP packets can be
decisive to the objectives we want to get through the device. The IP network is the fundamental infrastructure
for every industrial network so, although we cannot change the details of the IP implementation
in the operating systems of the devices, we need to know how to get the maximum performance
and reliability of our network for every industrial application we decide to use. It is also important to
note that the devices we can use to manage and implement these QoS characteristics are not the same
devices we use to implement our industrial applications but the usual communication devices in every
IP network—switches and routers. It is so possible to say that the QoS requirements in industrial networks
depend on the industrial applications we want to use and, as a consequence, of the complexity
of the network. If the network uses routers, we can apply special features in the routers to improve our
QoS; but if the network only needs switches, we can only use a restricted set of QoS features.
Any qualified network professional must know the limits for the networks in his or her organization.
It is necessary to know how to get the maximum of the features of the network devices used, being
switches, routers, or any network security element that can modify the network performance, as firewalls
or intrusion detection systems.
Until recently, there was not much to say about how to improve the services offered by IP networks. It
was enough that the network does its job properly 24.h/day. But today, and in almost every organization,
it is necessary a network be able to adapt the changing needs for the different kind of applications using
it as a means of transmission and communication. There will be applications that need more bandwidth
19-1
© 2011 by Taylor and Francis Group, LLC