1 QoS Model and Resource Management Issues for IEEE Std Chen-Nien Tsai Institute of Computer Science and Information Engineering National Taipei University of Technology

2 Outline ► Introduction ► QoS Model  Service Flow  Service Flow Management  Scheduling Services ► Resource Management Issues  Packet Scheduling  Bandwidth Allocation  Admission Control

3 Introduction ► IEEE defines several QoS related concepts:  Service Flow QoS Scheduling ► But do not specify how to do it.  Dynamic Service Management ► DSA/DSC/DSD messages. ► BS-initiated and SS-initiated  Two-phase Activation Model ► It is often utilized in telephony applications.

4 Introduction ► DOCSIS  Data-Over-Cable Service Interface Specifications. ► The QoS description and name conventions from DOCSIS were chosen as the basis for describing QoS in IEEE Std  Service flow ► Provisioned, admitted, and active.  Authorization Model Envelopes  QoS parameter sets

5 Service Flow ► A service flow is a unidirectional flow of packets that is provided a particular QoS. ► Service flows exist in both UL and DL direction and exist without actually being activated to carry traffic. ► All service flows have a 32-bit SFID; admitted and active service flows also have a 16-bit CID. admittedactive admittedactive

6 Object Model

7 Service Flow Attributes ► Service flow ID (SFID) ► Connection ID (CID)  Mapping to an SFID that exists only when the connection has an admitted or active service flow. ► ProvisionedQoSParamSet  A QoS parameter set provisioned via means outside of the scope of this standard. ► AdmittedQoSParamSet  A set of QoS parameters for which BS and SS are reserving resources.

8 Service Flow Attributes ► ActiveQoSParamSet  A set of QoS parameters defining the service actually being provided to the service flow. ► Authorization Module  A logical function within BS that approves or denies every change to QoS parameters and classifiers associated with a service flow.  Provisioned authorization module.  Dynamic authorization module.

9 Types of Service Flows ► Provisioned service flow  It is known via provisioning by the network management system.  AdmittedQoSParamSet and ActiveQoSParamSet are both null. ► Admitted service flow  It has resources reserved by the BS for its AdmittedQoSParamSet, but these parameters are not active.  ActiveQoSParamSet is null.

10 Types of Service Flows ► Active service flow  It has resources committed by the BS for its ActiveQoSParamSet.  ActiveQoSParamSet is not null.  For example, BS is actively sending maps containing unsolicited grants for a UGS-based service flow.

11 Service Class ► An optional object that may be implemented at the BS to have a particular QoS Parameter Set. ► Allow higher-layer protocols to create a service flow by its Service Class Name.  G711 for telephone signaling. ► Service flow contains either a full definition of QoS parameters or a service Class Name. ► When a Service Class name is used, the service flow can modify the parameters of the Service Class.

12 Service Class SSBS DSA-REQ Service Class = G711 DSC-REQ Wireless channel.... Maximum Sustained Traffic Rate = X ’ Maximum Latency= Y ’ DSA-REQ DSC-REQ.... Maximum Sustained Traffic Rate = X ’ Maximum Latency= Y ’ Maximum Sustained Traffic Rate = X Maximum Latency= Y

13 Scheduling Services ► Scheduling services represent the data handling mechanisms supported by the MAC scheduler for data transport on a connection.  Unsolicited Grant Service (UGS)  Real-time Polling Service (rtPS)  Extended rtPS (ertPS)  Non-real-time Polling Service (nrtPS)  Best Effort (BE)

14 Unsolicited Grant Service ► The UGS scheduling service type is designed to support real-time data streams consisting of fixed-size data packets issued at periodic intervals.

15 Real-time Polling Service ► The rtPS scheduling service type is designed to support real-time data streams consisting of variable-sized data packets that are issued at periodic intervals.

16 Extended rtPS ► It was added by the e amendment. ► ertPS is a scheduling mechanism that builds on the efficiency of both UGS and rtPS.  provides unicast grants in an unsolicited manner like in UGS.  ertPS allocations are dynamic. ► The ertPS is suitable for variable rate real- time applications that have data rate and delay requirements.

17 Non-real-time Polling Service ► The nrtPS is designed to support delay- tolerant data streams consisting of variable- size data packets for which a minimum data rate is required.

18 Best Effort ► The BE service is designed to support data streams for which no minimum service guarantees are required. ► A long period can run without transmitting any BE packets.

19 Usage Rules Scheduling Service Polling Contention Requests PiggyBack Requests Bandwidth Stealing UGS PM bit Not allowed rtPSUnicast AllowedAllowed ertPSUnicastAllowed Extended piggyback Allowed nrtPSAllAllowedAllowedAllowed BEAllAllowedAllowedAllowed

20 QoS Parameters ► Maximum Sustained Traffic Rate ► Maximum Latency ► Tolerated Jitter ► Request/Transmission Policy ► Minimum Reserved Traffic Rate ► Traffic Priority ► Maximum Traffic Burst ► Minimum Tolerable Traffic Rate

21 Mandatory QoS Parameters Scheduling Service Maximum Sustained Traffic Rate Minimum Reserved Traffic Rate Request/ transmission Policy Tolerated Jitter Maximum Latency Traffic Priority UGS★ (Can be presented) ★★★ rtPS★★★★ ertPS★★★★ nrtPS★★★★ BE★★★

22 Service Flow Management

23 Service Flow Management ► Creation  Pre-provisioned service flow ► It is done via means outside of the scope of this Std. ► Admitted or activated during Network Entry procedures.  Dynamic service flow ► Managed by DSA (add) message. ► Modification  Managed by DSC (change) message. ► Deletion  Managed by DSD (delete) message.

24 Dynamic Service Flow Creation ► Creation of a service flow may be initiated  by the BS (mandatory capability)  by the SS (optional capability) ► The DSA messages are used to create a new service flow (either uplink or downlink). ► The general format of DSA-REQ, DSA-RSP, and DSA-ACK messages: DSA-REQDSA-RSPDSA-ACKDSA-REQDSA-RSPDSA-ACK

25 Dynamic Service Establishment ► SS-initialed DSA  The standard does not go into details on what actually triggers the DSA.  Triggering is just assumed to happen, stimulated by the upper layers when needed. SS BS DSA-RSQ DSX-RVD Wireless channel DSA-RSP DSA-ACK This allows BS to take it time determining whether to admin the service flow

26 Dynamic Service Flow Creation ( SS-initialed DSA) SSBS Receive DSA-REQ Send DSX-RVD Check whether SS is authorized Check whether QoS can be supported Create SFID DSX-RVD DSA-REQ New service flow needed Check if resources are available Receive DSX-RVD Send DSA-REQ Wireless channel If AdmittedQoSParamSet is non- null, map service flow to CID If uplink ActiveQoSParamSet is non- null, enable reception of data on new service flow

27 Dynamic Service Flow Creation ( SS-initialed DSA) SSBS Send DSA-RSP Send DSA-ACK Wireless channel DSA-RSP DSA-ACK Receive DSA-RSP If ActiveQoSParamSet is non-null, enable transmission or reception of data on new service flow If downlink ActiveQoSParamSet is non-null, enable transmission of data on new service flow Receive DSA-ACK

28 Dynamic Service Establishment ► BS-initiated SS BS DSA-RSP DSA-RSQ Wireless channel DSA-ACK

29 Dynamic Service Flow Creation ( BS-initialed DSA) SSBS Receive DSA-REQ Send DSX-ACK New service flow required for SS Check whether SS is authorized Check whether QoS can be supported Create SFID DSX-REQ DSA-RSPSend DSX-RSP Send DSA-REQ Wireless channel If AdmittedQoSParamSet is non- null, map service flow to CID Enable transmission or reception of data on new service flow Confirm the SS can support service flow Add downlink SFID Enable reception on new downlink service flow Enable transmission on new uplink service flow Receive DSA-ACKDSX-ACK Receive DSA-RSP

30 Dynamic Service Flow Modification ► Created service flows are modified with the DSC message.  Change the admitted and active QoS parameter sets of the flow. ► QoS Parameter set type

31 QoS Parameter Set Type Values

32 SS-Initiated DSC SSBS Send DSX-RVD Receive DSC-RSP Wireless channel DSC-RSP DSC-ACK Send DSC-RSQ Service flow requires modifying Validate Request Modify service flow Increase channel bandwidth if required Receive DSC-ACK Modify service flow Adjust payload bandwidth Send DSC-ACK DSC-REQ DSX-RVD Receive DSC-RSQ Receive DSX-RVD Send DSC-RSP

33 BS-Initiated DSC SSBS Receive DSC-RSP Wireless channel DSC-RSP DSC-ACK Send DSC-RSQ Service flow requires modifying Validate Request Modify service flow Decrease payload bandwidth if required Receive DSC-ACK Modify service flow Adjust channel bandwidth Send DSC-ACK DSC-REQ Receive DSC-RSQ Send DSC-RSP Increase payload bandwidth if required

34 Dynamic Service Flow Deletion ► Any service flow can be deleted with the DSD messages. ► When a service flow is deleted, all resources associated with it are released.

35 SS-Initiated DSD SSBS Receive DSD-RSP Wireless channel DSD-RSP Send DSD-RSQ Service flow no longer needed Delete service flow Verify SS is service flow owner Delete service flow DSD-REQReceive DSD-RSQ Send DSD-RSP

36 BS-Initiated DSD SSBS Receive DSC-RSP Wireless channel DSD-RSP Send DSD-RSQ Service flow no longer needed Delete service flow Determine associated SS for this service flow Delete service flow DSD-REQReceive DSD-RSQ Send DSC-RSP

37 Two-phase Activation Model ► The resource for a call are first admitted, and then once the end-to-end negotiation is completed, the resources are activated. ► The purposes:  Conserving network resources until a complete end-to-end connection has been established.  Performing policy check and admission control on resources as quickly as possible.

38 Example 1 SSBS DSA-REQ Admitted MSTR = A ’ s request Active MSTR = 0 Perform admission control DSC-REQ Higher-level flow A is pending. Wireless channel Higher-level flow A is active Active MSTR = A ’ s request If active MSTR within the range of the previous reservation, this DSC- REQ is guaranteed to succeed. ► Suppose that an upper-layer service were using UGS. ► MSTR = Maximum Sustained Traffic Rate

39 Example 2 ► Suppose there are 4 higher-lever flows which are classified in a service flow. SSBS DSA-REQ Admitted MSTR = all flows ’ request Active MSTR = 0 Perform admission control DSC-REQ All flows are pending Wireless channel Higher-level flow A is active Admitted MSTR = all flows ’ request Active MSTR = A ’ s request If active MSTR within the range of the previous reservation, this DSC- REQ is guaranteed to succeed.

40 Resource Management Issues

41 Resource Management Issues ► BS  Contention Slot Allocation  Admission Control  Uplink Scheduling and Bandwidth Allocation  Downlink Packet Scheduling ► SS  Uplink Packet Scheduling ► BS & SS  Contention Resolution Algorithm ► Binary exponential backoff. (specified in the Std.)

42 Contention Slot Allocation ► BS can dynamically adjust the ratio of the bandwidth allocated to the contention slots.  Too few contention slots ► Increase the chances of bandwidth request collision. ► Reduce the amount of data that can be transmitted.  Too many contention slots ► Reduce the bandwidth left for data transmission.

43 SC Frame Structure

44 TDD Uplink Subframe

45 Uplink Transmission ► Three classes of bursts may be transmitted in a UL subframe:  Contention opportunities for initial ranging.  Contention opportunities for BW requests.  Contention-free periods assigned by BS to individual SSs.

46 Contention Slot Allocation Proposed in [1] ► N SSs in the system and backoff window size is B. ► The probability of choosing a given slot is ► The system throughput (no collision)

47 ► To maximize system throughput ► The maximum throughput can be obtained when B = N.

48 Packet Scheduling ► Three main scheduling points  Scheduling of the UL by the BS. ► Generates UL-MAP  Scheduling of the DL by the BS. ► Generates DL-MAP  Scheduling of the UL by the SS.

49 QoS Architecture Proposed in [2] BS ’ s DL Scheduler

50 Packet Scheduling ► Scheduler in the BS  Creates and distributes UL/DL MAP messages.  Must consider BW requests, polling, PHY maintenance needs, and current PHY mode. ► Scheduler in the SS  SS runs a scheduling algorithm but limited in scope to its own services.

51 Scheduler in the BS ► It is the role of the BS scheduler to determine the burst profile and the transmission periods for each connection.  UL/DL-MAP

52 Scheduling of the Different Services ► Recall that:  Each connection is assigned a scheduling service (via service flow).  Packets are classified in Convergence Sublayer. ► So …  The connection which the packets are placed is chosen based on the QoS requirements, which specify in the service flow.

53 Scheduling Service for Some Services ► Some of these services are mentioned in the standard.

54 BS Scheduler Operation for the UL

55 BS Scheduler Operation for the DL

56

57 Scheduling Algorithms ► Scheduling algorithms were intentionally left outside the scope of the IEEE Std ► Any of the known scheduling algorithms can be used:  Round Robin  Weighted Round Robin  Weighted Fair Queuing ► Many scheduling algorithms are being proposed for WIMAX/ in the literature.

58 Scheduling Algorithms Proposed in [2] ► BS ’ s uplink scheduler (creates UL-MAP)  Weighted Round Robin (WRR). ► SS ’ s scheduling strategy Priority Service Type Queuing Policy 1UGS Wireless Fair Queuing 2rtPS 3nrtPS WRR Scheduler 4BEFIFO

59 Admission Control ► Admission control is used to limit the number of connections/flows admitted into the network.  Individual connection/flow can get its desired QoS. ► Note that the types of services flows are  Provisioned  Admitted  Active Perform admission control when a service flow requests to change to one of these two types.

60 Admission Control Policy ► Admission control policy can be simple  First-In-First-Serve.  Considers only one QoS parameter. ► Maximum Sustained Traffic Rate ► Admission control policy can be complex  Considers multiple QoS parameter.  Advanced mechanisms ► Combines with bandwidth allocation. ► Dynamically adjust BW allocated to users. ► Preemptive

61 Admission Control Proposed in [3] ► Consider multiple QoS parameters  Maximum Sustained Traffic Rate for UGS, rtPS, and nrtPS.  Minimum Reserved Traffic Rate for nrtPS.  BE connections are always admitted. ► Dynamic bandwidth allocation.  For nrtPS only.  BS can allocates BW to a nrtPS connection base on the condition of the network. ► Lower BW allocated = more users can admitted.

62 Summary ► The service flows and connections are important concepts.  Service flows ► Identify the right of an SS to certain system resources. ► Define which of packets will be mapped to the corresponding connection.  Connections determine ► Which SS receives the data on the DL. ► What QoS and traffic parameters are associated with the traffic.

63 Summary ► Other issues  Rate Control  Power Control  Channel Assignment (OFDMA PHY)  Subcarrier Permutation (OFDMA PHY)

64 References [1] Dong-Hoon Cho, Jung-Hoon Song, Min-Su Kim, and Ki-Jun Han, “ Performance Analysis of the IEEE Wireless Metropolitan Area Network, ” Proceedings of the First International Conference on Distributed Frameworks for Multimedia Applications (DFMA ’ 05), Feb. 2005, pp [2] GuoSong Chu, Deng Wang, and Shunliang Mei, "A QoS Architecture for the MAC Protocol of IEEE BWA System," IEEE 2002 International Conference on Communications, Circuits and Systems and West Sino Expositions, vol. 1, June 2002, pp

65 References [3] Haitang Wang, Bing He, and Dharma P. Agrawal, “ Above Packet Level Admission Control and Bandwidth Allocation for IEEE Wireless MAN, ” Simulation Modelling Practice and Theory, vol. 15, issue 4, April 2007, pp [4] IEE Std , IEEE Standard for Local and Metropolitan Area Networks — Part 16: Air Interface for Fixed Broadband Wireless Access. [5] Carl Eklund et al., WirelessMAN: Inside the IEEE Standard for Wireless Metropolitan Area Networks, IEEE Press, [6] Loutfi Nuaymi, WiMAX: Technology for Broadband Wireless Access, John Wiley & Sons, 2007.

66 The End

67 Backup Materials

68 DSA-REQ and DSA-RSP

69 DSA-ACK and DSX-RVD

70 Service Flow Encodings

71 Confirmation Code

72 Authorization ► Every change to the service flow QoS Parameters shall be approved by an authorization module.  DSA-REQ message and DSC-REQ message. ► Such changes include requesting  admission control decision (setting the AdmittedQoSParamSet).  activation of a service flow (setting the ActiveQoSParamSet).

73 Provisioned Authorization Model ► The module stores the provisioned status of all deferred service flows. ► Admission and activation requests for those services flows are permitted as long as  AdmittedQoSParamSet ProvisionedQoSParamSet  ActiveQoSParamSet AdmittedQoSParamSet

74 Provisioned Authorization Model ► Those requests are refused:  Changing the ProvisionedQoSParamSet  Creating new service flows ► This defines a static system where all possible services are defined in the initial configuration of each SS.

75 Dynamic Authorization Model ► The module communicates to an independent policy server.  Policy server specifies the proper authorization action to be taken on requests. ► BS retrieves the ProvisionedQoSParamSet for an SS prior to initial connection setup.  It is handed to the authorization model.  BS use this information to authorize dynamic flows.

76 Dynamic Authorization Model ► Admission and activation requests from an SS  Are permitted if that are signaled in advance by the external policy server.  May result in a real-time query to the policy server if that are not presignaled by the external policy server.

77 Model Envelopes Authorization Module

78 Related Terms ► Connections ► Service Flow  Service flow ID  Provisioned, Admitted, Active.  QoS parameter sets ► Service Class ► Scheduling Service

79 ► Admission control and provisioning ► Traffic classification ► Shaping and policing ► Traffic scheduling

80 OFDM Frame Structure

81 OFDMA Frame Structure

82 Scheduling Algorithms in Packet Networks ► FIFO (First In, First Out)  FIFO +  No fairness and protection. ► Round-Robin  Weighted round-robin  Provides fairness and protection. ► Stop-And-Go

83 Scheduling Methods ► Round robin ► Proportional fair ► Max CINR ► Fair throughput ► Early deadline first

84 WirelessMAN-SC/SCa PHY ► Time is slotted. (Physical slots and minislots) ► Uplink  TDMA. ► Downlink  TDM ► Granularity of bandwidth allocation  One PS for DL  One minislot for UL.  1 minislot = 2 m PS (0 ≦ m ≦ 7)

85

86 QoS Architecture

87 QoS Architecture Proposed in [2]

88 Uplink Bandwidth Allocation Proposed in [1] ► UGS  BS always allocates bandwidth for UGS connections. ► rtPS  BS polls the SS according to the deadline. ► nrtPS  Uses either contention-free mode (low priority) or contention mode. ► BE  Uses contention mode only.

89 Uplink Bandwidth Allocation Proposed in [1] Service Type Contention-free mode Contention mode UGSN/AN/A rtPS High priority N/A nrtPS Low priority High priority BEN/A Low priority