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Introduction to Quality Of Service - Networking
Quality of service aims to provide different levels of priority to different applications, users or data flows. It guarantees a certain level of performance for data flows. Techniques to improve quality of service include scheduling, which treats different flows in a fair manner. Other techniques are FIFO queuing, priority queuing, weighted fair queuing, traffic shaping using leaky bucket and token bucket algorithms, resource reservation to reserve bandwidth and buffers beforehand, and admission control to restrict new packet flows.
Introduction to Quality Of Service - Networking
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- 2. So what isit? • Quality of service is the ability to provide different priority to different applications, users, or data flows, or to guarantee a certain level of performance to a data flow
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- 4. • Reliability :Lack of Reliability means losing a packet or ack. • Delay : Different applications can tolerate delay in different degrees. • Jitter : jitter is the variation in packets belonging to same flow. • Bandwidth : different application need different b/w.
- 5. Techniques to improve thequality of service. Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control
- 6. Scheduling • Packets fromdifferent flow arrive at switch or router for processing • A good scheduling technique treats the different flow in a fair and appropriate manner
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- 8. • FIFO QUEUING •Packets wait in a buffer (queue) until the node is ready to process them. • If avg. arrival rate>avg. processing rate =>new packets will be discarded.
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- 10. • Packets areassigned to a priority class • Each class has its own queue. • Higher class packets are processed first. • Problem : Starvation Priority Queuing
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- 12. • Packets arestill assigned to different classes and admitted to different queues • The queues are weighted based on the priority • Higher priority means higher weight • If weight are 3,2,1 then 3 packets are processed from q3,2 from q2,and 1 from q1 in a round robin fashion Weighted Fair Queuing
- 13. Traffic Shaping Is themechanism to control the amount and the rate of the traffic sent to the network
- 14. Techniques to improve thequality of service Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control
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- 16. The rate atwhich water leaks from a bucket does not depend on the rate at which the water is input to the bucket The input rate varies but the o/p remains constant ,similarly ,network can smooth out bursty traffic Leaky Bucket
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- 18. Token Bucket Leaky bucketdoes not taken into a/c idle host , if a host is not sending for a while , its bucket becomes empty. If the host has bursty data ,leaky bucket allows only avg. rate. Token bucket takes into a/c the idle time , with each clock tick the tokens are added to bucket ,when the data needs to be send ,it collects token from bucket and then send the data packet consisting of data=no of tokens
- 19. Techniques to improve thequality of service Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control
- 20. Resource Reservation • Aflow of data needs resources such as buffer, bandwidth, CPU time, and so on . • QoS can be improved if these resources are reserved beforehand.
- 21. Techniques to improve thequality of service Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control
- 22. Admission Control • Routersor switches puts restrictions on the admission of packets from host. • Before a router accepts the flow , it checks the flow for specifications in terms of bandwidth , buffer size ,cpu speed etc.
- 23. Conclusion: Flow characteristics Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control
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