An Efficient QoS Scheduling Architecture for IEEE Wireless MANs Supriya Maheshwari Under the guidance of Prof. Sridhar Iyer and Prof. Krishna Paul

Broadband Wireless Access

Broadband Wireless Access (Contd…) High demand for “last-mile” broadband access. Advantages of Broadband Wireless Access Fast deployment and high scalability. High speed network access at low cost. Broad geographic area. IEEE WirelessMAN standard for Broadband Wireless Access systems.

Need for a QoS Scheduling Architecture for IEEE IEEE has been designed to support QoS in both downlink and uplink directions. IEEE proposes uplink scheduling services and request-grant mechanisms to provide different levels of services for various classes of uplink traffic. Main component to accomplish this task i.e. packet scheduling mechanism is unspecified.

Bandwidth Request-Grant Protocol BS SS 1 SS BS allocates bandwidth to SSs for transmitting bandwidth request. 2.1 SS 1 transmits bandwidth requests. 2.2 SS 2 transmits bandwidth requests. 4. BS allocates bandwidth to SSs for transmitting data based on their bandwidth requests. Bandwidth is also allocated for requesting more bandwidth. 5.1 SS 1 transmits data and bandwidth requests. 5.2 SS 2 transmits data and bandwidth requests

Need for a QoS Scheduling Architecture for IEEE BS completely controls transmission in downlink direction. Request-Grant protocol is used for uplink bandwidth allocation which involves both BS and SS. Uplink Scheduling is complex as it needs to be in accordance with uplink QoS provisions provided by IEEE Therefore, a single scheduling algorithm for the whole system does not suffice.

Problem Statement Propose an efficient QoS scheduling architecture for IEEE Wireless MANs. Design Goals To provide delay and bandwidth guarantees for various kinds of applications. To maintain fairness among various flows based on their priority. To achieve high bandwidth utilization.

IEEE Features WirelessMAN air interface for fixed point to multi- point Broadband Wireless Access GHz frequency range. Supports channel as wide as 28 MHz and data rate upto 134 Mbps. Provides QoS support for various applications. Bandwidth on demand. Link adaptation. High security.

Contd… Downlink and Uplink channel. Supports both TDD and FDD. Downlink channel is a broadcast channel. Uplink is shared among all SSs through DAMA-TDMA The TDD Frame

The Downlink Subframe The Uplink Subframe

Existing QoS Provisions of IEEE MAC Service Flows Uplink Scheduling Services Unsolicited Grant Service (UGS) Support applications generating constant bit rate traffic periodically. Provides fixed bandwidth at periodic intervals. Real-Time Polling Service (rtPS) Supports real-time applications generating variable bit rate traffic periodically. Offers periodic opportunities to request bandwidth. Non Real-Time Polling Service (nrtPS) Supports non-real-time applications generating variable bit rate traffic regularly. Offers opportunities to request bandwidth regularly. Best Effort (BE) Offers no guarantee.

Bandwidth Requests and Grants Ways Bandwidth request packet. Piggybacking bandwidth request with normal data packet. Request can be made during time slot assigned by base station for sending request or data. Grant modes Grant per Connection (GPC). Grant per Subscriber Station (GPSS).

Proposed QoS Scheduling Architecture for IEEE Design Goals To provide bandwidth and delay guarantees to various applications and maintain fairness among various flows while still achieving high bandwidth utilization. Uses GPSS mode. Scalable and efficient. Smaller Uplink control information. Suitable for real-time applications which require faster response. Enhances system performance. Supports all types of service flows.

Working of Components BS/SS Data Classifier Maps an IP packet to a particular connection. BS/SS Traffic Shaper Examines and shapes the incoming traffic. BS Periodic Grant Generator Grant at t k = t 0 + k * Interval Deadline = t k + Jitter BS Uplink Grant Classifier Maps each grant to the corresponding SS.

Working of Components (Contd…) BS Frame Partitioner Divides total frame bandwidth equally between downlink and uplink subframe. SS Request Generator For each connection, aggregate request based on current queue length is generated. BS Uplink Map Generator Allocates bandwidth to each SS for uplink transmission. Uses two stage max-min fair allocation strategy. Order of transmission among SSs is decided based on deadline of UGS data.

Example Total Uplink Bytes = SS and 1 BS SS 1 Demands: UGS = 20 rtPS = 12 nrtPS = 15 BE = 30 SS 2 Demands: UGS = 10 rtPS = 10 nrtPS = 15 BE = 20 Total Demand Per Flow: UGS = 30 rtPS = 22 nrtPS = 30 BE = 50 Flows: UGS rtPSnrtPSBE 1 st Round Excess Bytes = 18 2 nd Round Excess Bytes = 2 3 rd Round SS 1 Allocation = = 56 SS 2 Allocation = = 44

Working of Components (Contd…) BS Downlink Scheduler Reserved flows are served using WFQ scheduling algorithm. Remaining bandwidth is allocated to unreserved flows. SS Uplink Scheduler Separate queue for each connection except for nrtPS and BE flows with no reservation, divided into four categories. UGS flows are served first. rtPS and reserved nrtPS and BE flows are served using WFQ scheduling. Remaining bandwidth is allocated to unreserved flows.

Implementation Details Qualnet 3.6 Network Simulator is used for simulation. IEEE b PHY as physical layer.

BS State Transition Diagram

SS State Transition Diagram

Simulation Setup Frame Duration=10ms Bandwidth=11Mbps Channel is assumed to be error-free. Performance Metrics Effective Bandwidth Utilization Average Delay

Effective Bandwidth Utilization Vs Offered Load [Scenario 1] Offered load by UGS > rtPS > nrtPS > BE Maximum Effective Bandwidth Utilization ~ 93%

Effective Bandwidth Utilization Vs Offered Load [Scenario 2] Offered load by UGS < rtPS < nrtPS < BE Maximum Effective Bandwidth Utilization ~ 93%

Effective Bandwidth Utilization Vs Number of SS [Scenario 1] Offered load by UGS > rtPS > nrtPS > BE Maximum Effective Bandwidth Utilization ~ 88%

Effective Bandwidth Utilization Vs Number of SS [Scenario 2] Offered load by UGS < rtPS < nrtPS < BE Maximum Effective Bandwidth Utilization ~ 88%

Average Delay Vs Number of SS Maximum Subscriber Stations ~ 15

Average Delay Vs Time [Scenario 1] Offered load by UGS > rtPS > nrtPS > BE UGS and rtPS flows experience low delay.

Average Delay Vs Time [Scenario 2] Offered load by UGS < rtPS < nrtPS < BE UGS and rtPS flows experience low delay.

Average Delay Vs Time [Scenario 3] Fairness is maintained among flows across SSs Three SSs with different type of uplink flows. SS 1 - UGS and rtPS SS 2 - UGS and nrtPS SS 3 - UGS and BE

Conclusion An efficient QoS scheduling architecture for IEEE is necessary to provide required QoS guarantees to various applications. Proposed an efficient QoS scheduling architecture for IEEE IEEE MAC has been implemented in Qualnet 3.6 along with the proposed architecture. Simulation results are presented to show that our architecture fulfills the stated design goals.

Future Work Contention slot allocation algorithm can be designed. Admission control mechanism can be devised. Performance Study of IEEE MAC over IEEE b PHY.

References IEEE “IEEE Standard for Local and Metropolitan Area Networks - Part 16: Air Interface for Fixed Broadband Wireless Access Systems”. Apr. 8, GuoSong Chu, Deng Wang, and Shunliang Mei. “A QoS architecture for the MAC protocol of IEEE BWA system”. IEEE International Conference on Communications, Circuits and Systems and West Sino Expositions, 1:435– 439, June Mohammed Hawa and David W. Petr. “Quality of Service Scheduling in Cable and Broadband Wireless Access Systems”. Tenth IEEE International Workshop on Quality of Service, pages 247–255, May Abhay K. Parekh and Robert G. Gallagher. A generalized processor sharing approach to flow control in integrated services networks: the multiple node case. IEEE/ACM Trans. Netw., 2(2):137–150,

References C. Eklund, R. B. Marks, K. L. Stanwood, and S. Wang, “IEEE Standard : A Technical Overview of the WirelessMAN TM Air Interface for Broadband Wireless Access”, IEEE Communications Magazine, 40(6): , June Andrew S. Tanenbaum, Computer Networks, Prentice-Hall India, Fourth edition, S. Keshav. An Engineering Approach to Computer Networking. Pearson Education, Sixth edition, 2003.