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Quality of Service
Quality of service aims to provide different levels of priority to different applications, users, or data flows. It is achieved through techniques like scheduling, traffic shaping, resource reservation, and admission control. Scheduling methods include FIFO queuing, priority queuing, and weighted fair queuing. Traffic shaping uses leaky bucket and token bucket algorithms. Resource reservation reserves buffer space, bandwidth, and other resources beforehand. Admission control restricts packet admission based on specifications. Models for QoS include the Integrated Services Model, which requires resource reservation in advance using RSVP, and the Differentiated Services Model, which differentiates traffic into classes.
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Quality of Service
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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
- 3. “ it definesthe quality of service as something a flow seeks to attain”
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- 5. • 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.
- 6. Techniques to improve thequality of service. Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control
- 7. 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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- 9. • 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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- 11. Priority Queuing • Packets areassigned to a priority class • Each class has its own queue. • Higher class packets are processed first. • Problem : Starvation
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- 13. Weighted Fair Queuing • Packetsare still 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 q1,2 from q2,and 1 from q1 in a round robin fashion
- 14. Traffic Shaping Is themechanism to control the amount and the rate of the traffic sent to the network
- 15. 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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- 17. Leaky Bucket The rateat which 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
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- 19. Token Bucket Leakybucket does 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
- 20. Techniques to improve thequality of service Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control
- 21. 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.
- 22. Techniques to improve thequality of service Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control
- 23. 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.
- 24. Models deploying QoS •Two models have been designed to provide QoS: ->Integrated Service Model(IntServ) ->Differentiated Service Model(Diffserv)
- 25. IntServ • User needsto create flow, kind of virtual circuit ,from source to destination and inform all routers of requirement
- 26. RSVP: Resource Reservation Protocol •Receiver based reservation : the receiver not the sender make the reservation(eg : youtube) • RSVP messages: ->Path Messages ->Resv Messages
- 28. DiffServ • The routerroutes the packet based in the class of service defined in the packet • It defines several classes such as ,constant bit rate class , the variable bit rate class etc.
- 29. DiffServ* • ToS: typeof service field is used to define the class of service for each packet
- 30. DiffServ* • ToS: typeof service field is used to define the class of service for each packet
- 31. Conclusion: Flow characteristics Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING Traffic Shaping LEAKY BUCKET TOKEN BUCKET Resource Réservation Admission Control Models Integrated Model (Requirement in advance) Differentiated Model(Classes)
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