Traffic Control

1. Traffic Control Prof. Nelson Fonseca State University of Campinas

2. Traffic • Traffic – bits carried; • Ultimate goal of a network – to transport bits.

3. Traffic Control • Support of the Quality of Service requirements of the applications; • Efficient use of network resources.

4. Quality of Services • Perception of the quality of information transport.

5. Quality of Services • QoS parameters: express numerically specific aspects of the quality perceived • Common parameters: • Mean delay; • Loss rate;

6. transmission A propagation B processing queueing Delay in Packet Switching Networks • Node processing checksum table lookup • ququeing • Wait for output link • Depends on node congestion Packets expreice delay in their end-to-end path Four delay components

7. Transmission delay: R=bandwidth (bps) L=packet size (bits) Time to put the bits in the link = L/R transmission A propagation B processing queueing Delay in Packet Switching Networks Propagation delay • d = length of the link • s = propagation speed (~2x108 m/sec) • Propagation delay=

8. R=link bandwidth (bps) L=packet size (bits) a=arrival rate of packets Queueing Delay traffic intensity = La/R • La/R ~ 0: low mean delay • La/R -> 1: increasing delay • La/R > 1: work arrived exceeds processing capacity

9. Jitter • Delay variation • Impact on playback of voice applications • Buffer at receiver to ammeliorate jitter effect

10. An Example:ATM QoS Parameters • Maximum transfer delay • Delay variation peak to peak; • Cell Loss rate; • Rate of block severiously lost; • Rate of cells erroneously inserted.

11. QoS Parameters • Number of packets consecutively lost; • Mena time between faults; • Mean time to have access; • Mean time to recover from faults.

12. Traffic Descriptors • Characterizes quantitatively the pattern of the flow of bits • Used to produce estimates of the resource demands of a flow

13. An Example:ATM Traffic Descriptors • Peak Cell Rate (PCR): Maximum rate of cell transmission; • Sustainable Cell Rate (SCR): upper bound for the transmission rate; • Burst Tolerance – (BT) • Maximum Burst Size - maximum time for transmission at peak rate

14. An Example:ATM Traffic Descriptors

15. Class of Service • Users´choices of agreemet on quality of transport made between service provider • Usually classes of services exists at the network/link layer to support users´expectation of QoS

16. An Example:ATM Class of Services • CBR; • NRT – VBR; • RT – VBR; • ABR; • UBR; • GRF.

17. CBR • Constant Bit Rate; • Allocation of fixed amount of bandwidth during the duration of the virtual circuit; • Real-time applications are sensitive to delay and minimum bandwidth; • Voice, video, circuit emulation.

18. CBR

19. RT – VBR • Real Time Variable Bit Rate; • Time-varying requirements of bandwidth; • Applications which need delay bound • Voice and video.

20. NRT – VBR • Non-Real Time Variable Bit Rate; • Data-loss sensitive applications; • Time-varying bandwidth requirements.

21. VBR

22. ABR • Avaliable Bit Rate; • Bandwidth allocation depends on network feedback; • Not proper to delay sensitive applications.

23. ABR

24. UBR • Unspecified Bit Rate; • Serviço Best Effort; • Ip over ATM; • No QoS guarantees.

25. GRF • Generalized Frame Rate; • Enhanced Serviço Best Effort; • Minimum bandwidth guarantees; • Deals with frames intead of cells;

26. Class of Service

27. Congestion • Network lack of capacity to provide the Quality of Service requirements of applications

28. QoS

29. Congestion Control • Congestion control mechanisms work at different time scales and can be either reactive or pro-active

30. Congestion Control Mechanisms • Admission control • Policing • Selective Discard • Active queue management • Scheduling

31. Controle de Admissão de Conexão (CAC) • Decision making process. Decides whether or not to accept a flow (connection) into a network domain; • Decisions need to consider the mantainance of QoS requirements of already admitted flows as well as the support of QoS requirements of requesting flows;

32. Admission Control My requirements are.... My traffic parameters are... Service provider

33. Admission Control Traffic descriptors Traffic representation Estimation of total resource demand

34. Admission Control Parametric (analytical models) Two approaches Measurement Based

35. Admission ControlParametric Approach

36. Admission ControlParametric Approach

37. Admission ControlParametric Approach

38. Admission ControlMeasurement Based • Traffic Envelopes MBAC: • Arrival Envelope: describes the peak rate over defined intervals. • Service Envelope: describes the minimum service received by a traffic class as a function of interval length. destination egress router source ingress router

39. Admission Control Measurement Based • Admission Control condition: • R(t) = mean of the arrival envelope • 2 = variance of the arrival envelope • S(t) = mean of the service envelope • 2 = variance of the service envelope • P = peak rate of the new flow • D = delay bound •  = violation probability

40. Admission Control Measurement Based • Stability condition:

41. Admission Control Measurement Based • Time-Window/Measured Sum MBAC: • The decision algorithm admits a new flow with load f if:  + f < C *  f: load of the new flow. : measured load of existing traffic. C: channel capacity. : user-defined utilization target.

42. Admission Control Measurement Based • Time-Window/Measured Sum MBAC:  + f <  * C  + f <  * B *  B: maximum data rate used by the network. : estimate of the channel efficiency.

43. Admissible Region

44. Admissible Region

45. Centralized Admission Control

46. Distributed Admission Control

47. Interdomain Admission Control Arquiteturas para Provisão de QoS na Internet

48. Admission ControlWireless Network • Admission Control aware of: • Signal to interference and noise ratio • Handoff failure

49. Admission ControlWireless Network

50. Admission ControlWireless Network