QoS (Quality of Service) refers to a broad collection of
networking technologies and techniques. The goal of
QoS is to provide guarantees on the ability of a network
to deliver predictable results. Elements of network
performance within the scope of QoS often include
availability (uptime), bandwidth (throughput), latency
(delay), and error rate. QoS involves prioritization of
network traffic. QoS can be targeted at a network
interface, toward a given server or router's performance,
or in terms of specific applications. A network monitoring
system must typically be deployed as part of QoS, to
insure that networks are performing at the desired level.
QoS is especially important for the new generation of
Internet applications such as VoIP, video-on-demand
and other consumer services. Some core networking
technologies like Ethernet were not designed to support
prioritized traffic or guaranteed performance levels,
making it much more difficult to implement QoS solutions
across the Internet.
Quality of Service is “The collective effect of service
performances which determine the degree of satisfaction
of a user of the service”, According to the definition of
ITU (International Telecommunication Union).
The main QoS requirements are:
Bandwidth :represents a data stream bandwidth.
Reliability : represents the tolerance for losses in a
Delay :The relative delay between packets and the
round Trip Delay.
The actual QoS assigned to a stream depends on many parameters:
the server scheduling algorithm,
the server priority settings,
the server load,
the scheduling cost.
Internet supports best-effort service only. The existing
applications are time-sensitive, delay-sensitive, jittersensitive or have other importance requirements
which are not supported by best-effort Internet.
Differentiated services which aims to:
Classify the traffic into groups
Handles different traffic groups differently.
Collective service to put the traffic demands in
domain, and to Limit the demand & the reserve
I. Differentiated Services
Services (DiffServ ) means a
multiple service model that can satisfy the most
DiffServ is used for several mission-critical
applications and to provide end-to-end QoS.
DiffServ reduces the burden on network devices
and easily scales as the network grows.
Differentiated Services Components
Traffic conditioning: (or traffic policing and traffic
shaping)to ensure that traffic entering the DiffServ
Packet classification: It uses a traffic descriptor to
categorize a packet within a specific group.
Packet marking: to classify a packet based on a
specific traffic descriptor.
Congestion management: achieve scheduling and
Congestion avoidance to monitor network traffic loads
to avoid congestion at common network bottlenecks. It
may be achieved through packet dropping.
The main components of a DiffServ network:
The Differentiated Model goal is to Divide the Traffic into Classes
Best Effort Delivery
Differentiated Services ( DiffServ or DS) represents a
computer networking architecture that specifies a
simple, scalable and coarse-grained mechanism for
classifying, managing network traffic and providing
Quality of Service
A Differentiated Model is a model that is appropriate for
management of current corporate network resources
II. Integrated Services
services (IntServ) is an architecture to specify
the elements to guarantee QoS.
IntServ can be used to delete the receiver interruption for
the video and sound.
The IntServ idea is to let every router in the system
implements IntServ, and let every application requires
some kind of guarantees to make an individual reservation.
The integrated services structure can be implemented
through the following components:
the signaling protocol.
the admission control routine.
II. Integrated Services con.
the classifier .
the packet scheduler.
This model requires explicit signaling mechanism
to convey information to routers so that they can
provide the requested resources.
RSVP is one of the most widely known example of
such a signaling mechanism.
Comparison Diffserv VS Intserv
aims to mark the packets
with priority and send it to
the network. No prior
reservation of resources
are involved in diffserv.
involves prior reservation
sending to achieve the
• Per aggregation
• Per aggregation
• Per flow isolation
• Per flow
• No isolation
• No guarantees
•Long term setup
• Per flow setup
• Highly scalable
• (nodes maintain
only routing state)
• Scalable (edge
state; core routers
per class state)
• Not scalable
The main two traffic management frameworks are:
Differentiated Services (DS, DiffServ):
helps to classify the traffic into a number of traffic groups and
handle it based on the traffic group.
Integrated Services (IS, ISA, IntServ):
based mainly on reserving resources per session and limit total
demand to the capacity that can be handled by the network.
Technical, Commercial and Regulatory Challenges of QoS: An
Internet Service Model Perspective by Xipeng Xiao (Morgan
Kaufmann, 2008, ISBN 0-12-373693-5)
Deploying IP and MPLS QoS for Multiservice Networks: Theory and
Practice by John Evans, Clarence Filsfils (Morgan Kaufmann,
2007, ISBN 0-12-370549-5)
QoS Over Heterogeneous Networks by Mario Marchese (Wiley,
2007, ISBN 978-0-470-01752-4)
Teletraffic Engineering Handbook ITU-T Study Group 2 (350 pages,
4·48MiB)(It uses abbreviation GoS instead of QoS)