IEEE 802.16 QoS Architecture for Efficient Bandwidth Management

1. IEEE 802.16QoS Architecture 2010/03/31黃筱婷

2. Outline 1. Introduction 2. IEEE 802.16 QoS Architecture 3.Bandwidth Request 4.Transmission Scheduling 5. Conclusion

3. Introduction 802.16 Deployment

4. Introduction

5. Introduction • Service-Specific Convergence Sublayer(CS): • CS層主要負責接收不同上層網路封包和進行分類，並與CID做連接。 • 處理由MAC CPS層傳送上來的資料。 • MAC Common Part Sublayer(MAC CPS): • 802.16 MAC層發展的主要層面 • 定義了基本的BS與SS之間維持網路運行的management訊息、執行流程、QoS支援、頻寬分配與ARQ(AutomaticRepeatRequest)重傳機制等。 • Security Sublayer: 主要定義加密技術，無線網路無法得知是否有人再擷取BS或SS 的廣播訊號，因此需要有加密機制來防範。 • Physical Layer : 負責資料的調變與解調變，錯誤更正碼。若使用OFDM，則包括FFT。

6. Introduction

7. Introduction

8. Outline 1. Introduction 2. IEEE 802.16 QoS Architecture 3.Bandwidth Request 4.Transmission Scheduling 5. Conclusion

9. QoSmechanisms • Classification • Mapping from MAC SDU fields (e.g destination IP address) to CID and SFID • Scheduling • Downlink scheduling module • Simple, all queues in BS • Uplink scheduling module • Queues are distributed among SSs. • Queue states and QoS requirements are obtained through BW requests. • Algorithms not defined in standard

10. IEEE 802.16 QoS Architecture

11. Service Types

12. Service Types (cont.)

13. Service Types (cont.) • Extended rtPS (ErtPS) • 結合UGS和rtPS的排程機制 • 支援具即時性但傳輸量不固定的資料流，Ex: silence suppression的VoIP • BS可以跟UGS一樣提供週期性的unicastgrants • 當SS要傳輸ertPS資料流時，就要先告知BS其QoS參數，當連線建立後，和UGS類似，BS會主動分配其頻寬；而當頻寬需求改變時，SS可以發出頻寬需求告知BS網路頻寬的需求量。另外，SS也可以透過bandwidth stealing或是piggyback的方式提出頻寬要求。除此之外，此類服務也在競爭期間發出頻寬需求。

14. Service Types (cont.)

15. Service Types (cont.)

16. priority 高 低 Comparison Table

17. Poll/Grant Options in Scheduling Services

18. Outline 1. Introduction 2. IEEE 802.16 QoS Architecture 3.Bandwidth Request/Allocation 4.Transmission Scheduling 5. Conclusion

19. Bandwidth Management • Bandwidth(BW) for a connection is allocated on a demand assignment basis. Unused bandwidth allocation will be withdrawn. • Bandwidth is managed via Request/Grant Methods. • UGS services aren’t necessary to be requested,since the resource needs are known in advance. • Request can be used for all other services. • Bandwidth can’t taken from a UGS service (it’s guaranteed) while possible for other services.

20. Unicast polling • Polled Request: polling sent from BS • Unicast polling • Sent on SS’s basic CID • Transmission opportunities in Request IE or Data Grant IE • Data Grant IE can use a more efficient burst file • Request IE can only use the Request IE burst file(UIUC=1) • Unicast polling of an SS would normally be done by allocating a Data Grant IE directed at its Basic CID • The transmission of BRs is contention-free

21. Unicast polling(cont.) Unicast polling

22. Multicast polling and broadcast polling • Multicast polling and broadcast polling • Sent on multicast CID or broadcast CID • Only the members in the polled group will send BRs • BRs are transmitted in a contention way and the contention resolution algorithm is applied • BS shall individually poll the SSs periodically who don’t have bandwidth allocated • With only one active UGS connection(BW stealing and piggyback aren’t allowed), SS set ‘PM’ bit asking BS to poll the SS • In case no enough bandwidth available for individual polling, broadcast or multicast polling are used

23. Multicast polling and broadcast polling(cont.) Multicast and broadcast polling

24. Bandwidth Stealing • Bandwidth Stealing • SS uses a portion of allocated bandwidth for a connection for a connection to send another bandwidth requests rather than sending data • Not allowed for UGS connection

25. Piggyback Request • Piggyback Request • The bandwidth request is piggybacked onto a MAC PDU on an existing connection with allocated bandwidth • Not allowed for UGS connection • The request is unsuccessful if no grant has been received in next few UL-MAP message

26. Bandwidth Allocation • 802.16標準的MAC集中式架構中BS scheduler能夠控制radio interface等參數來決定DL及UL的存取 • 依據requested bandwidth, QoS parameters 和available resources 來決定頻寬 • Grant Per Subscriber Station (GPSS)：BS根據每一個SS（Subscriber Station）的連線要求來分配時槽，SS端之下，會有許多種類的連線，BS將SS下的所有連線視為一個實體的連線去分配與控制時槽。每個SS再自行根據底下所管轄的每個連線要求去分配每個連線的時槽。

27. Bandwidth Allocation (cont.) • Downlink • BS根據不同的參數來決定DL的頻寬配置 • 考慮QoS的情況下連接及傳輸所需的流量，BS scheduler會調整連結，並決定哪個SS將取得downlink burst(s)和適當的burst profile • Uplink • SS必須遵守傳輸協定並且BS控制SS彼此間的競爭，以確保每一個使用者應用程式傳輸服務的延遲和頻寬需求 • UL的傳輸必須考慮並對應到五種QoS類別 (UGS, rtPS, ertPS, nrtPS, and BE) • BS以下列四種方法實現UL存取及頻寬配置 • unsolicited bandwidth grants • piggyback bandwidth request • unicast polling (polling) • contention-based procedures (broadcast or multicast polling)

28. Outline 1. Introduction 2. IEEE 802.16 QoS Architecture 3.Bandwidth Request 4.Transmission Scheduling 5. Conclusion

29. BS scheduler operation for UL

30. Transmission Scheduling • Radio resources have to be scheduled according to the QoS (Quality of Service) parameters • Uplink Scheduling • the scheduling algorithms can be used : • RR (Round Robin) • WRR (Weighted Round Robin) • WFQ (Weighted Fair Queuing) • WFFQ (Worst-case Fair weighted Fair Queuing) • VT (Virtual Time) • DRR (Deficit Round Robin) • DDRR (Distributed Deficit Round Robin) • EDF (Earliest Deadline First)

31. WRR (Weighted Round Robin) • The WRR algorithm is based on the Round Robin algorithm but it takes into account the processing capacity of each waiter. • The administrators manually assign a coefficient of performance to each waiter. ( 1, 2 and 3 in the example).

32. WFQ (Weighted Fair Queuing)

33. EDF (Earliest Deadline First) • A dynamic scheduling algorithm used in real-time operating systems. • It places processes in a priority queue. Whenever a scheduling event occurs (task finishes, new task released, etc.) the queue will be searched for the process closest to its deadline. • If there is a feasible schedule, then EDF produces a feasible schedule

34. Scheduling Example • “Packet scheduling for QoS support in IEEE 802.16 broadband wireless access systems”中設計了一個排程演算法來達到QoS並增 進WiMAX的效能。 • This scheduling algorithm isproposed to assign: • a fixed bandwidth for UGS, • using Earliest Deadline First (EDF) technique for rtPS, • Weighted Fair Queuing (WFQ) for nrtPS and • equal distribution for BE.

35. BS scheduler operation for DL

36. Outline 1. Introduction 2. IEEE 802.16 QoS Architecture 3.Bandwidth Request 4.Transmission Scheduling 5. Conclusion

37. Conclusion • IEEE802.16針對MAC層做了特殊的設計，將載波切分成許許多多的subchannel來傳送，提供較已往更具彈性及效率的機制。 • IEEE802.16所定義的五種QoS資料型態，如何有效的傳送以滿足各 traffic不同的需求，配合排程的概念，使系統不致因新用戶的進入而導致服務品質的降低，對於real-timetraffic 還必須符合latency與jitter的需求，並且依照各類 traffic QoS的高低順序來優先使用time slots • 在設計有效排程時必須確保QoS並有公平的資源分配。 • Wimax可能建構於複雜的環境中，在惡劣的環境中channel的品質很差並不罕見，但會實際的影響到理論上公平的排程和本身滿足QoS的能力。因此確認channel的品質是設計良好packet scheduling的重要因素

38. Future Work • 3G/LTE, Wi-Fi等網路架構的QoS • 對各種排程方法做更深入的研究 • 嘗試找出能增進效能的排程演算法, 並使其適用於異質網路

39. Reference [1] IEEE Std 802.16-2009 [2] A. Ganz, Z.GanzandK.Wongthavarawat ,Multimedia Wireless Networks: Technologies, Standards, and QoS, Prentice Hall PTR, 2003, ch.7 [3] L. Nuaymi, WiMAX: Technology for Broadband Wireless Access, Wiley, 2007, ch.11 [4] K. Wongthavarawat, and A. Ganz, “Packet Scheduling for QoS Support in IEEE 802.16 Broadband Wireless Access Systems”, International Journal of Communication Systems, Vol. 16, p81-96, 2003 [5] K. R. Raghu, S. K. Bose, and M. Ma, “Queue Based Scheduling for IEEE 802.16 Wireless Broadband,” in Proc. 6th IEEE Int. Conf. ICICS, 2007, pp. 1–5 [6] 張致恩, 無限都會網路系統與技術短期課程,2009

40. Q&A Thanks for your attention!