We propose an efficient request-based uplink bandwidth allocation algorithm for variable-rate real-time service in broadband wireless access networks. By introducing a notion of target delay under the framework of dual feedback, the proposed algorithm can regulate delay while minimizing delay jitter and bandwidth waste.

The emerging broadband wireless access technology based on IEEE 802.16 is one of the most promising solutions to provide ubiquitous wireless access to the broadband service at low cost. This paper proposes an efficient uplink bandwidth request-allocation algorithm for real-time services in Mobile WiMAX networks based on IEEE 802.16e. In order to minimize bandwidth wastage without degrading quality of service (QoS), we introduce a notion of target delay and propose dual feedback architecture. The proposed algorithm calculates the amount of bandwidth request such that the delay is regulated around the desired level to minimize delay violation and delay jitter for real-time services. Also, it can increase utilization of wireless channel by making use of dual feedback, where the bandwidth request is adjusted based on the information about the backlogged amount of traffic in the queue and the rate mismatch between packet arrival and service rates. Due to the target delay and dual feedback, the proposed scheme can control delay and allocate bandwidth efficiently while satisfying QoS requirement. The stability of the proposed algorithm is analyzed from a control-theoretic viewpoint, and a simple design guideline is derived based on this analysis. By implementing the algorithm in OPNET simulator, its performance is evaluated in terms of queue regulation, optimal bandwidth allocation, delay controllability, and robustness to traffic characteristics.

In this paper, we investigate the issue of per-station fairness in TCP over IEEE 802.11-compliant wireless local area networks (WLANs), especially in Wi-Fi hot spot. It is asserted that the hot spot suffers from the unfairness among stations in exploiting the wireless medium. The source of this unfairness is analyzed from two aspects, TCP-induced asymmetry and MAC-induced asymmetry; the former causes TCP congestion control with a cumulative acknowledgment mechanism to prefer the sending stations to receiving stations, while the later exacerbates the unfairness problem in the hot spots. We investigate the interaction between TCP congestion control and MAC contention control, and propose a cross-layer feedback approach to assure per-station fairness and to ensure high channel utilization. In this approach, we introduce the notion of channel access cost to quantify the system-wide traffic load and per-station channel usage. The access cost is estimated at the MAC in an access point and conveyed to the TCP sender. Then, the TCP sender adjusts its sending rate based on the access cost, so as to assure per-station fairness. The simulation results indicate that the proposed approach can provide both per-station fairness and high channel utilization, irrespective of network configurations.

As public deployment of wireless local area networks (WLANs) has increased and various applications with different service requirements have emerged, fairness and quality of service (QoS) are two imperative issues in allocating wireless channels. This study proposes a fair QoS agent (FQA) to simultaneously provide per-class QoS enhancement and per-station fair channel sharing in WLAN access networks. FQA implements two additional components above the 802.11 MAC: a dual service differentiator and a service level manager. The former is intended to improve QoS for different service classes by differentiating service with appropriate scheduling and queue management algorithms, while the latter is to assure fair channel sharing by estimating the fair share for each station and dynamically adjusting the service levels of packets. FQA assures (weighted) fairness among stations in terms of channel access time without decreasing channel utilization. Furthermore, it can provide quantitative service assurance in terms of queuing delay and packet loss rate. FQA neither resorts to any complex fair scheduling algorithm nor requires maintaining per-station queues. Since the FQA algorithm is an add-on scheme above the 802.11 MAC, it does not require any modification of the standard MAC protocol. Extensive ns-2 simulations confirm the effectiveness of the FQA algorithm with respect to the per class QoS enhancement and per-station fair channel sharing

Differentiated service (DiffServ) networks have been proposed to assure the achievable minimum bandwidth to aggregate flows. However, analyses in the literature show that the current DiffServ networks are biased in favor of ah aggregate flow that has a smaller committed information rate (CIR) when aggregate flows with different CIRs share a bottleneck link. In order to mitigate this unfairness problem, we propose an adaptive marking scheme which provides the relative bandwidth assurance in proportion to the CIRs of the aggregates. By introducing a virtual target rate (VTR) and adjusting it depending on the provision level of the network, each aggregate can obtain its fair share of the bandwidth, regardless of traffic load. This scheme is based on a feedback approach. It utilizes only two-bit feedback information conveyed in the packet header and can be implemented in a distributed manner. Furthermore, the proposed scheme does not require calculating fair shares of aggregates or any additional signaling protocol. Using steady state analysis and extensive simulations, we show that the scheme can provide aggregate flows with their fair shares of bandwidth, which is proportional to the CIRs, under various network conditions

This paper focuses on the unfairness problem between TCP uplink and downlink flows in the 802.11 Wi-Fi hot spots and shows that the service is prone to be unfair. The cause of unfairness is analyzed from two aspects: TCP-induced asymmetry and MAC-induced asymmetry. Due to the asymmetric behavior of TCP congestion control with a cumulative acknowledgment mechanism between uplink and downlink flows, the service is biased toward the uplink flow and the downlink flow tends to starve. The contention-based channel access mechanism of 802.11 MAC exacerbates this unfairness problem because it intends to provide fair access opportunity only to the sending stations. Next, the analysis of the interaction between congestion control of TCP and contention control of MAC reveals interesting and counter-intuitive results: (i) Even when a station has a sufficiently large amount of traffic to send, it does not always participate in the MAC-layer contention, its opportunity for MAC-layer contention is controlled by the TCP congestion control, (ii) The aggregate throughput remains almost constant with respect to the number of stations sending/receiving TCP traffic. (Hi) Both TCP-induced unfairness and MAC-induced unfairness can be resolved if packet loss due to buffer overflow in an access point does not occur.

By analyzing the steady state throughput of TCP flows in differentiated service (DiffServ) networks, we show that current DiffServ networks are biased in favor of those flows that have a smaller target rate, which results in unfair bandwidth allocation. In order to solve this unfairness problem, we propose an adaptive marking scheme, which allocates bandwidth in a manner which is proportional to the target rates of the aggregate TCP flows in the DiffServ network. This scheme adjusts the target rate according to the congestion level of the network, so that the aggregate flow can obtain its fair share of the bandwidth. Since it utilizes edge-to-edge feedback information without measuring or keeping any per-flow state, this scheme is scalable and does not require any additional signaling protocol or any significant changes to the current TCP/IP protocol. It can he implemented in a distributed manner using only two-bit feedback information, which is carried in the TCP acknowledgement. Using extensive simulations, we show that the proposed scheme can provide each aggregate flow with its fair share of the bandwidth, which is proportional to the target rate, under various network conditions.

We propose an adaptive token bucket algorithm for achieving proportional sharing of bandwidth among aggregate flows in differentiated service (DiffServ) networks. By observing the simulation results obtained in a study of the throughput of TCP flows in a DiffServ network, we note that the aggregate flow with a lower target rate occupies more bandwidth than its fair share, while the aggregate flow with a higher target rate gets less than its fair share. The proposed algorithm solves this unfairness problem by adjusting the target rate according to the edge-to-edge feedback information. This algorithm does not require any additional signaling protocol or measurement of pen-flow states, since it can be implemented in a distributed manner using only two-bit feedback information carried in the TCP acknowledgement. Using ns-2 simulations, we show that the proposed algorithm provides fair bandwidth sharing under various network conditions.

The virtual rate control (VRC) algorithm has been proposed for active queue management (AQM) in TCP networks. This algorithm uses an adaptive rate control instead of queue length control in order to respond quickly to traffic change with high utilization and small loss. By introducing the notion of virtual target rate, the VRC algorithm can maintain an input rate around the target rate, while attempting to regulate the queue length. In this paper, we analyze the stability of the VRC algorithm in a linearized model. From the results of our analysis, we provide a design guideline for the system to remain stable. We show the validity of our analysis and the effectiveness of the VRC algorithm compared to RED, PI, REM and AVQ algorithms through ns-2 simulations.