Dynamic Polling Access Control for High Density Subscribers in Wireless WiMAX Networks CSIE & NC Chaoyang University of Technology Taichung, Taiwan, ROC Ben-Jye Chang & Chien-Ming Chou Good afternoon, ladies and gentlemen. I am Chien-Ming Chou from Chaoyang University of Technology in Taiwan. The title of this paper is “Adaptive Polling Algorithm for Reducing Polling Delay and Increasing Utilization for High Density Subscribers in WiMAX Wireless Networks”. TANET2006 GNW, Chaoyang University of Technology

Outline Introduction Motivations Adaptive switch of Polling mode access Control (APC) approach for WiMAX Numerical Results Conclusions I’ll present follow the outline. First, the introduction and problem about WiMAX using polling access control protocol on internet are discussed. Then, the proposed adaptive polling approach for WiMAX is described in detail. Next show the numerical results. Finally, take a conclusion for this paper. TANET2006

What is polling in WiMax? IEEE 802.16 adopts polling mechanism instead of random access for avoiding contention among requests. Active node: Base Station (BS) Passive node: Subscriber Station (SS) Advantages Overcome the request collisions Support 4-type QoS service flows Disadvantages Polling delay (linear growing based on the number of SSs) For achieving contention free among requests, IEEE 802.16 adopts the polling mechanism instead of random access. It brings some advantages including - Overcome the request collisions - Support 4-type QoS service flows But brings long polling delay when the number of SSs is large. TANET2006

Why needs services flow ? Satisfy different application classes Real time service flow UGS for VoIP rtPS for video streaming Non-real time service flow nrtPS for FTP BE for HTTP or e-mail Combination of call admission control with polling access control to management resource. WiMAX supprots 4 classes of service flow for QoS-aware transmission. The 4 types service flows, including UGS and rtPS for real time service classes and nrtPS and BE for non-real time service classes. WiMAX also suggests to provide a Call Admission Control for managing resource allocation among these 4 classes of service flow. TANET2006

An example of Polling in WiMAX As the slide shown is an example of polling mechanism. The BS polls each SS based on a specified polling list, which is shown in blue color. If the residual bandwidth is not enough for a new bw request, the BS will switches from the unicast polling to the multicast polling mode. In multicast polling, the BS polls each group in turn and the SSs belong to the same group have data to be send will reply a bw request with a random contention value when they are polled. TANET2006

Contention in total SSs Type of polling (cont.) Polling modes Feature Unicast Multicast Broadcast How many to polling Individually Groups A group Use time Default If insufficient bandwidth is available to individually poll many inactive SSs Advantage Contention free Polling delay(↓) NO polling delay Disadvantage Polling delay(↑) Contention in group Contention in total SSs Services classes UGS ※ rtPS ● X nrtPS BE The slide shows the supported service flow which can be serviced in these 3 polling modes. In which, all classes of service flow can be serviced in unicast polling mode. But rtPS can not be serviced in group polling mode because in such polling modes the bandwidth requests in the same group is performed as a contention manner and thus can not guarantee access delay. ※：In the UGS service flow, BS will allocate a fixed bandwidth of UGS for all registered SSs. X：rtPS service flow can not be scheduled in the multicast / broadcast polling. TANET2006

What are the challenges in WiMAX ? Long polling delay Since the large number of SSs brings a long polling delay and causes not to meet the QoS guarantee of real-time services. rtPS is not allowed to be polled by multicast polling Cause long access delay while BS is in multicast polling So what are the main challenges in WiMAX? We list two main challenges: First, WiMAX yields long polling delay when the number of SSs is large, i.e., in the case of high density of SS within a BS. Second, since it can not guarantee access delay in group polling’s contention based access, WiMAX does not support rtPS in group polling. It causes long waiting delay of rtPS when it is in group polling modes.. TANET2006

Motivations Propose an efficient polling algorithm for WiMAX Improve the rtPS service flow can not be polled in multicast polling mode Overcome large number of SSs brings a long polling delay Therefore, the motivations of this paper have 2: First, we propose a new Quasi-rtPS, namely QrtPS, to take over the original rtPS when a BS switches to multicast polling mode. Second, to overcome long polling delay when a BS is in multicast polling mode. ------------------------- First, because the rtPS service flow only can be scheduled in unicast polling, then system convert from unicast to multicast mode time. The rtPS service flow can’t be scheduled in multicast polling lead to increase waiting delay time. Second, Using unicast polling since the a lot number of SSs bring about a long polling delay and causes not to meet the QoS guarantee of real-time services. TANET2006

APC approach A novel service class of quasi rtPS (QrtPS) is proposed Using QrtPS service flow taking over the rtPS service to be scheduled continuously while in the multicast polling mode. Two-phase approach Phase 1: Switching the polling mode Using Hysteresis to reduce the ping-pong effect between the unicast and multicast polling modes. Phase 2: Efficient contention resolution algorithm Propose a QrtPS service flow with an efficient contention resolution algorithm in multicast polling for continuing scheduling the original rtPS. Regarding to the proposed Adaptive Polling Approach, We first propose an QrtPS service class that is used to take over rtPS when in multicast polling. Then, a two-phase mechanism is proposed to achieve the advantages In the first phase, we adopt a hysteresis mechanism to avoid the ping-pong effect between the unicast and multicast polling modes. In the second phase, an efficient contention algorithm is proposed to guarantee QrtPS can be polled in prior nrtPS and BE service flows. TANET2006

QoS parameters Traffic priority QrtPS > nrtPS > BE Service Classes QoS Parameters UGS rtPS QrtPS nrtPS BE Maximum Sustained Traffic Rate  Maximum Delay Average Delay Tolerated Jitter Request/ Transmission Policy Minimum Reserved Traffic Rate Traffic Priority Traffic priority QrtPS > nrtPS > BE The slide shows the QoS parameters of our proposed QrtPS and the WiMAX 4 service classes. The main different between QrtPS and rtPS is that QrtPS only supports average delay but rtPS supports Maximum delay. TANET2006

APC Phase 1. Switching the polling mode with hysteresis Unicast to Multicast Case 1 (time) : Case 2 (BW) : Multicast to unicast Case 1 (time) : Case 2 (BW) : In WiMAX, a BS can be switched from uniast to multicast polling mode when the available bandwidth is not enough for the new request connection. Upon a single threshold, it causes unnecessary switch and brings large overhead while switching. Therefore, the the phase I in the proposed adaptive polling approach, we adopt bandwidth and the number of SSs with individual hysteresis for overcoming ping-pong effect between the unicast and multicast polling modes, in which S_1 and S_2 are the thresholds for each QoS parameter. enough BW insufficient small Number of SSs many TANET2006

APC Phase 2: Efficient Contention resolution The advantage of the proposed QrtPS with an efficient contention resolution algorithm in multicast polling for continuing scheduling the original rtPS. The polling delay of the original rtPS class can be improved. Backoff windows： QrtPS < nrtPS < BE In WiMAX’s group polling mode, several SSs belong to the same group may require bandwidth at the contention value and cause collision. Moreover, for guaranteeing higher-class service can be serviced before lower-class service, we adopt different access priorities for different classes. That is, QrtPS is the highest one, then is the nrtPS, and BE is the lowest class. TANET2006

APA Flow Diagram Phase 1 Phase 2 Finally, the flow diagram of the proposed adaptive polling approach is shown in the slide. The left side is the BS node and the right side is the SS node. The yellow block in BS is the proposed polling criteria (that is the phase 1) and that in SS is the efficient contention resolution mechanism (that is the phase 2). Phase 2 TANET2006

Performance metrics Average delay Network utilization Tradeoff items Polling delay + queue delay Network utilization Tradeoff items Number of groups Number of contention slots The proposed APA mechanism is evaluated by average delay and network utilization. TANET2006

Simulation Parameters , Network model Traffic model This slide shows the simulation results for the evaluations. The red and green blocks are the parameters for the network and traffic models, respectively. In the traffic model, we consider two traffic types of Poisson and Pareto distributions for real time and non real time services, respectively. Network model TANET2006

The average delays of rtPS and nrtPS of different approaches under various NDSs Good IEEE 802.16 This slide shown the average delay of rtPS and nrtPS of different approaches under various NDS. The X axis is NDS and Y axis is the average delay. From this figure we can see that the delays of IEEE 802.16 are larger than that of the proposed APC. Especially, APC outperforms IEEE 802.16 in delay when they are in multicast polling mode, which results from the QrtPS service. APC NGS = 20 Contention slots = 32 TANET2006

Utilization of different approaches under various NDSs APC Good IEEE 802.16 This slide shown the Utilization of different approaches under various NDS. The X axis is NDS and Y axis is the utilization. From this figure we can see that the utilization of IEEE 802.16 is lower than that of the proposed APC. The QrtPS contributes to the high utilization in APC. NGS = 20 Contention slots = 32 TANET2006

Collision probabilities of different contention slots under various NGS This slide shown the Average delay of rtPS in APC with Collision probabilities of different contention slots under various NGS . The X axis is NGS and Y axis is the average of rtPS. Good NDS = 400 TANET2006

Conclusions The Proposed an APC approach to determine the polling mode in a high-density SSs WiMAX Can for minimizing the average delay and maximizing network utilization. The case of NCS=16 yields the optimal collision probability and average delay. Finally, we take a conclusion of this paper. TANET2006

Q & A Thank you changb@mail.cyut.edu.tw s9430612@cyut.edu.tw Above is my presentation of this paper, any question? TANET2006

Type of polling IEEE 802.16 supports 3 types of polling Unicast polling Multicast polling Broadcast polling In WiMAX, three polling modes are adopted, including unicast, multicast and broadcast modes. In the unicast polling, a BS polls a SS within a frame time. In multicast and broadcast polling, the BS polls a group of SSs within a frame time. TANET2006