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QoS Model and Resource Management Issues for IEEE Std. 802.16

QoS Model and Resource Management Issues for IEEE Std. 802.16. Chen-Nien Tsai Institute of Computer Science and Information Engineering National Taipei University of Technology 2007.11.19. Outline. Introduction QoS Model Service Flow Service Flow Management Scheduling Services

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QoS Model and Resource Management Issues for IEEE Std. 802.16

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  1. QoS Model and Resource Management Issues for IEEE Std. 802.16 Chen-Nien Tsai Institute of Computer Science and Information Engineering National Taipei University of Technology 2007.11.19

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

  3. Introduction • IEEE 802.16-2004 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 802.16. • 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.

  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. DSA-REQ DSA-REQ DSC-REQ DSC-REQ Service Class SS Wireless channel BS Service Class = G711 . . Maximum Sustained Traffic Rate = X’ Maximum Latency= Y’ 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 802.16e 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

  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

  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:

  25. Wireless channel BS DSX-RVD SS DSA-RSQ DSA-ACK DSA-RSP 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. This allows BS to take it time determining whether to admin the service flow

  26. DSA-REQ DSX-RVD Dynamic Service Flow Creation( SS-initialed DSA) SS Wireless channel BS New service flow needed Check if resources are available Send DSA-REQ Receive DSA-REQ Send DSX-RVD Receive DSX-RVD Check whether SS is authorized Check whether QoS can be supported Create SFID 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. DSA-ACK DSA-RSP Dynamic Service Flow Creation( SS-initialed DSA) SS Wireless channel BS Receive DSA-RSP Send DSA-RSP If ActiveQoSParamSet is non-null, enable transmission or reception of data on new service flow Send DSA-ACK Receive DSA-ACK If downlink ActiveQoSParamSet is non-null, enable transmission of data on new service flow

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

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

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

  33. DSC-REQ DSC-ACK DSC-RSP BS-Initiated DSC SS Wireless channel BS Service flow requires modifying Receive DSC-RSQ Send DSC-RSQ Validate Request Modify service flow Decrease payload bandwidth if required Send DSC-RSP Receive DSC-RSP Modify service flow Adjust channel bandwidth Receive DSC-ACK Send DSC-ACK 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. DSD-REQ DSD-RSP SS-Initiated DSD SS Wireless channel BS Service flow no longer needed Delete service flow Send DSD-RSQ Receive DSD-RSQ Verify SS is service flow owner Delete service flow Receive DSD-RSP Send DSD-RSP

  36. DSD-REQ DSD-RSP BS-Initiated DSD SS Wireless channel BS Service flow no longer needed Delete service flow Determine associated SS for this service flow Receive DSD-RSQ Send DSD-RSQ Delete service flow Send DSC-RSP Receive 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. DSA-REQ SS Wireless channel BS DSC-REQ Higher-level flow A is pending. Perform admission control Admitted MSTR = A’s request Active MSTR = 0 . . . . Higher-level flow A is active. If active MSTR within the range of the previous reservation, this DSC-REQ is guaranteed to succeed. Active MSTR = A’s request Example 1 • Suppose that an upper-layer service were using UGS. • MSTR = Maximum Sustained Traffic Rate

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

  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.

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