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Published byRosamund Bell Modified over 8 years ago
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Muhammad Mateen Yaqoob Department of Computer Science COMSATS Institute of Information Technology, Abbottabad 1
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As broadband networking technology has dramatically increased the capacity of packet-switched networks Every applications have diverse QoS requirements QoS depends on the statistical nature of traffic An appropriate service model should be defined QoS control methods should be engineered to meet a range of QoS performance requirements 2
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Two main traffic types delay-sensitive traffic (characterized by rate and duration and may need real-time transmission) loss-sensitive traffic (characterized by the amount of information transmitted) Other traffic types Such as playback traffic, multicast traffic, and traffic aggregation 3
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Network has been evolving to provide QoS guarantees ATM can reserve the bandwidth and buffer for each virtual connection Intserv can also provide QoS for each flow in IP network Diffserv provides different treatment for packets of different classes, instead of on a flow basis, so that it has better scalability than Intserv MPLS allows the network providers to have better control and provision of QoS through traffic engineering policies 4
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Key QoS design and deployment best practices that can simplify and expedite QoS implementations includes; Classification and marking principles Policing and markdown principles Queuing and dropping principles DoS and worm mitigation principles Deployment principles 5
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A number of QoS parameters can be measured and monitored to determine whether a service level offered or received is being achieved Network availability Bandwidth Delay Jitter Loss 6
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There are also QoS performance-affecting parameters that cannot be measured but provide the traffic management mechanisms for the network routers and switches Emission priority Discard priority Each of these QoS parameters affects the application’s performance or end-user’s experience 7
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If the network is unavailable then the user or application may achieve unpredictable or undesirable performance Network availability is the collection of the availability of many items that are used to create a network The greatest challenge for network operators today is to provide highly available IP networks 8
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It is sub-divided into two types: Available bandwidth; amount of bandwidth (in bps) available for allocation Subscriber competes for allocation of available bandwidth Guaranteed bandwidth; minimum amount of bandwidth (in bps) guaranteed by network operator to be allocated for the subscriber The service price is high 9
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Network delay is the transit time an application experiences from the access point to the exit point of the network Delay can cause significant QoS issues with applications such as voice and video Some applications can compensate for small amounts of delay but once a certain amount is exceeded, the QoS becomes compromised Delay can be fixed or variable 10
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Jitter is the measure of delay variation between consecutive packets for a given traffic flow Jitter has a pronounced effect on real-time, delay-sensitive applications such as voice and video As arrival rate varies, jitter impacts application’s performance A minimal amount of jitter may be acceptable but as jitter increases, the application may become unusable 11
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Loss can occur due to errors introduced by the physical transmission medium Loss can also occur when congested network nodes drop packets If congestion continues, network performance will significantly decrease because much of bandwidth is being used to retransmit dropped packets 12
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Emission priorities determine order in which traffic is forwarded as it exits a network node Traffic with a higher emission priority is forwarded ahead of traffic with a lower emission priority Emission priorities also determine amount of latency introduced to the traffic by the network node’s queuing mechanism 13
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Discard priorities are used to determine order in which traffic gets discarded Traffic may get dropped due to network node congestion or when traffic is out-of-profile Traffic with similar QoS performance requirements can be subdivided using discard priorities This allows the traffic to receive the same performance when the network node is not congested 14
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