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Quality of service

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Outline Introduction Qos Definition QoS Parameters QoS Architecture MPLS IntServ DiffServ Conclusion

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Introduction

Lack of management mechanism of network resources in the protocols (IP, TCP, FTP, etc ....) led the IETF (Internet Engineering Task Force) to provide technical (or models) for better management of bandwidth .

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Definition of QoS

The QoS is a tool implemented in networks to guarantee the transport of data in the best possible end to end.

The idea of QoS is to transport some priority flows (from real-time applications in general) compared to the other in good conditions.

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QoS parameters

It is necessary to assess more accurately the QoS parameters according to which the goal is to continuously improve it :

Delay. Jitter. Dropped packets. Throughput. Availability. Out-of-order delivery.

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Congestion

In general we define the congestion of a network by the slow performance the latter due to over use leads to saturation.

Thus the definition most accurate in our case study is the concentration of traffic sources to a single destination (the router) that is why architectures have been developed to reduce the micro-congestions.

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QoS Architecture

MPLS (MultiProtocol Label switching).

IntServ (Integrated Service).

DiffServ (Differentiated Services).

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QoS Architecture

The determination of the appropriate type of service deployed in a network depends on several factors :

The nature of the application.

The flow that can reach customers.

The cost of implementation and deployment of the architecture and its performance.

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MPLS Architecture

The idea of MPLS is to combine between layer 2 and 3 of the OSI model to optimize and accelerate the speed of packet processing in all intermediate equipment.

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MPLS Architecture

This architecture is characterized by a label (or label) fields of 32 bits which is added as header packets in the network or MPLS cloud.

MPLS allows then to act on the packet switching and thus to specify paths to classes of traffic.

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IntServ Architecture

IntServ was the first architecture, QoS, it is based on the approach by bandwidth reservation to ensure quality of service real-time applications.

This reservation is made using RSVP (Resource Reservation Protocol), this protocol makes the reservation of resources by spreading requests (bandwidth) on all the routers along the path (PATH) from end to end.

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IntServ Architecture

Advantages:

Reservation of resources from start to finish.

Dedicate a portion of the bandwidth.

Precise management of the network.

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IntServ Architecture

Disadvantages : Used for small networks.

Reporting to the ongoing maintenance of the connection from end to end.

Unsuitable for Internet.

Each router must maintain a state which is not easy to do.

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DiffServ

In contrast to the IntServ architecture that is processing on data streams, DiffServ enables processing flows per class or type of flows more accurately, it decreases significantly the state information that each node in the network must memorize.

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DiffServ

The idea is then to divide DiffServ routers in the network into two categories, therefore different routers inside the network packets that carry the "core routers" (Core Router), and access routers and edge (Edge Routers) that classify packets (tagging).

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DiffServ

On the way to routing, service differentiation is achieved by combining DSCP field contained in the header of the IP packet to a particular treatment of "forwarding", at each node on the path.

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DiffServ

Advantages:

A distinction flows per class.

Each network node performs a different treatment according to priority and network congestion.

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DiffServ

Disadvantages :

The setup process is very complex equipment which leads to static configurations that do not change frequently.

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Conclusion

QoS required.

Meaning complex and underestimated.

Needs specific to the company.

Customizing QoS.

Emergence of a new job.