1. Department of Computer and IT Engineering University of Kurdistan Computer Networks II Quality of Service (QoS) By: Dr. Alireza Abdollahpouri

2. What is QoS?  Some applications require “deliver on time” assurances  must come from inside the network  Example application (audio)  sample voice once every 125us  each sample has a playback time  packets experience variable delay in network  add constant factor to playback time: playback point Microphone Speaker Sampler A D converter Buffer, D A 2

3. What can go wrong with IP? 1) IP packet is lost 2) IP packet is delayed IP network Best effort is not enough 3

4. 4 QoS Parameters In packet-switched networks, QoS is affected by various factors including  Bandwidth  Delay  Jitter  Packet loss

5. 5 Bandwidth

6. 6 Delay

7.  Delay is the time required for a signal to traverse the network. Time Received Sent Latency Data Packet 7

8. 8 Jitter High jitter Low jitter.

9. Jitter Data Packet Time Received Sent Jitter Variable interpacket timing caused by the network a packet traverses. Jitter میتواند به دلیل صف بندی در مسیریابها و یا عبور بسته ها از مسیرهای مختلف اتفاق بیفتد Jitter میتواند به دلیل صف بندی در مسیریابها و یا عبور بسته ها از مسیرهای مختلف اتفاق بیفتد 9

10. 10 دلایل اتلاف بسته تاثیراتلاف بسته Packet loss

11. 11 تصویر ارسالی تصویر دریافتی QoS vs. QoE (Quality of Experience) QoS: کیفیت از لحاظ پارامترهای شبکه QoE: کیفیت از دید کاربر QoS: کیفیت از لحاظ پارامترهای شبکه QoE: کیفیت از دید کاربر

12. QoS requirements for different applications 12

13. Traffic descriptors 13

14. Constant-bit-rate traffic (CBR) Variable-bit-rate traffic (VBR) Bursty traffic Traffic types 14

15. Applications  Elastic (delay-tolerant)  Tolerate delays and losses  Can adapt to congestion  Non-elastic (Real-Time)  Needs some kind of guarantee from network  Main Question? How guarantee Delay and losses  End to End, is it enough?  In the Network 15

16. 16 Techniques to Improve QoS Packet scheduling techniques (e.g., FIFO, Priority Queuing, WFQ) Traffic Shaping techniques (e.g., Leaky Bucket, Token Bucket) Resource reservation techniques (e.g., RSVP) Admission Control techniques (mechanisms used by a router or a switch to accept or reject a flow based on flow specifications) Traffic monitoring and feedback

17. 17 Scheduling

18. 18

19. Playback Buffer Sequence number Packet generation Network delay Buffer Playback Time Packet arrival 19

20. FIFO queue Scheduling 20

21. Priority queuing Scheduling 21

22. Weighted fair queuing Scheduling 22

23. 23 Traffic shaping

24. Leaky bucket Traffic Shaping b bits r b/s 24

25. A leaky bucket algorithm shapes bursty traffic into fixed-rate traffic by averaging the data rate. It may drop the packets if the bucket is full. Note: 25

26. 26 Leaky bucket does not credit an idle host. If a host is not sending for a while, bucket becomes empty. The idle time of a host is not considered in leaky bucket. In token bucket, idle hosts accumulate credit for the future in the form of tokens. Leaky bucket drawback

27. Token bucket Traffic Shaping 27

28. Token Bucket Algorithm: Calculating the length of the maximum rate burst.  Burst length S second.  Token bucket capacity C bytes  The token arrival rate p bytes/sec  The maximum output rate M bytes/sec S=C/(M-p)  Example: C=250KB, M=25MB/sec, p=2MB/sec. In this case S=11msec.

29. Question: A computer on a 6-Mbps network is regulated by a token bucket. The token bucket is filled with a rate 1 Mbps. The bucket is initially filled to capacity with 1 Mb. How long can the computer transmit at the full 6 Mbps? Answer: The net outflow from the token bucket is 5Mbps. As a result, the time it takes for the full bucket to empty is 1Mb/5Mbps=0.2sec. Thus, during the first 0.2 seconds the computer transmits at the maximum 6-Mbps rate and then it switches to 1-Mbps. Token bucket - example 29

30. The Leaky and token Bucket example (a)Input to a leaky bucket. (1 MB burst). Network speed is 200 Mbps (b) Output from a leaky bucket (2MB/sec), 1 MB bucket size Output from a token bucket with capacities of (c) 250 KB, (d) 500 KB, 30

31. The token bucket allows bursty traffic at a regulated maximum rate. Note: 31

32. 32 Resource reservation

33. Resource reservation  “A flow of data needs resources such as buffer, bandwidth, CPU time..”  The quality can be improved by reserving these resources in beforehand  The flow doesn’t need to compete with other flows 33

34. Integrated Service  Enhancing IP Service Model  Add QoS service classes  Explicit resource management at IP level  Per flow state maintained at routers which is  used for admission control and scheduling  set up by signaling protocol, users explicitly request their needs.  This is done with RSVP protocol 34

35. RSVP Resource reservation protocol RSVP is not a routing protocol. It relies on a routing protocol to provide a route/tree along which it sends control messages to make reservation. 35

36. Basic Operations of RSVP  Sender sends PATH message via the data delivery  Each router adds its state and the address of the pervious hop  Receiver sends RESV message on the reverse path  Specifies the reservation style, QoS desired  Set up the reservation state at each router 36

37.  Achieve per-flow bandwidth and delay guarantees  Example: guarantee 1Mbps and < 100 ms delay to a flow Sender Receiver Path RSVP Message 37 Integrated Services Example (RSVP)

38. Sender Receiver  Allocate resources - perform per-flow admission control RESV RSVP Message 38 Integrated Services Example (RSVP)

39. Sender Receiver  Install per-flow state 39

40. Sender Receiver  Install per flow state RESV RSVP Message 40 Integrated Services Example (RSVP)

41. Sender Receiver  Per-flow classification 41 Integrated Services Example (RSVP)

42. Sender Receiver  Per-flow buffer management 42 Integrated Services Example (RSVP)

43. Sender Receiver Per-flow scheduling 43 Integrated Services Example (RSVP)

44. 44 Admission control

45. Admission control  mechanism used by a router or a switch to accept or reject a flow based on flow specifications 45 احتمال بروز تراکم در شبکه ای که ا زAC استفاده می کند پایین تر است. چرا که این مکانیزم ، جامعیت ترافیک موجود در شبکه را با جلوگیری از پذیرش سایر ترافیکها حفظ می نماید.

46. QoS Issues on wireless  Dynamically varying network topology  Imprecise state information  Lack of central coordination  Error-prone shared radio channel  Hidden terminal problem  Limited resource availability  Insecure medium 46

47. 47 QuestionsQuestions