Quality of Service

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Quality of Service

  1. 1. Quality of Service By: Abhishek Wadhwa, BVICAM
  2. 2. So what is it? • 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. 3. “ it defines the quality of service as something a flow seeks to attain”
  4. 4. Flow Characteristics
  5. 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. 6. Techniques to improve the quality of service.  Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING  Traffic Shaping LEAKY BUCKET TOKEN BUCKET  Resource Réservation  Admission Control
  7. 7. Scheduling • Packets from different flow arrive at switch or router for processing • A good scheduling technique treats the different flow in a fair and appropriate manner
  8. 8. • FIFO QUEUING
  9. 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.
  10. 10. Priority Queuing
  11. 11. Priority Queuing • Packets are assigned to a priority class • Each class has its own queue. • Higher class packets are processed first. • Problem : Starvation
  12. 12. Weighted Fair Queuing
  13. 13. Weighted Fair Queuing • Packets are 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. 14. Traffic Shaping Is the mechanism to control the amount and the rate of the traffic sent to the network
  15. 15. Techniques to improve the quality of service  Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING  Traffic Shaping LEAKY BUCKET TOKEN BUCKET  Resource Réservation  Admission Control
  16. 16. Leaky Bucket http://www.epubbud.com/read.php?g=5HEKFDZU&two=1&tocp=48
  17. 17. Leaky Bucket The rate at 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
  18. 18. Token Bucket
  19. 19. Token Bucket  Leaky bucket 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. 20. Techniques to improve the quality of service  Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING  Traffic Shaping LEAKY BUCKET TOKEN BUCKET  Resource Réservation  Admission Control
  21. 21. Resource Reservation • A flow of data needs resources such as buffer, bandwidth, CPU time, and so on . • QoS can be improved if these resources are reserved beforehand.
  22. 22. Techniques to improve the quality of service  Scheduling FIFO QUEUING PRIORITY QUEUING WEIGHTED FAIR QUEUING  Traffic Shaping LEAKY BUCKET TOKEN BUCKET  Resource Réservation  Admission Control
  23. 23. Admission Control • Routers or 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. 24. Models deploying QoS • Two models have been designed to provide QoS: ->Integrated Service Model(IntServ) ->Differentiated Service Model(Diffserv)
  25. 25. IntServ • User needs to create flow, kind of virtual circuit ,from source to destination and inform all routers of requirement
  26. 26. RSVP: Resource Reservation Protocol • Receiver based reservation : the receiver not the sender make the reservation(eg : youtube) • RSVP messages: ->Path Messages ->Resv Messages
  27. 27. DiffServ • The router routes 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.
  28. 28. DiffServ* • ToS: type of service field is used to define the class of service for each packet
  29. 29. DiffServ* • ToS: type of service field is used to define the class of service for each packet
  30. 30. 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)
  31. 31. Any Questions?
  32. 32. Thank You
  33. 33. References • • • • • • • • cisco.tu-sofia.bg/uploads/Additional/Cisco_QoS.pdf www.cs.columbia.edu/~coms6181/slides/13/quality-of-service.ppt www.cs.princeton.edu/courses/archive/spr03/cs461/lec12/lec12.ppt www.csb.uncw.edu/people/.../Topic%207%20Service%20Quality.p pt http://www.rfceditor.org/search/rfc_search_detail.php?rfc=2474&title=quality+of+s ervice&pubstatus%5B%5D=Any&pub_date_type=any http://www.epubbud.com/read.php?g=5HEKFDZU&two=1&tocp=48 *for further reading ->page 9 of Cisco_QoS.pdf http://www.rfc-editor.org/

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