Wenqing Cheng

Adaptive congestion control for DSRC vehicle networks

Dedicated short range communications (DSRC) was proposed for collaborative safety applications (CSA) in vehicle communications. In this article we propose two adaptive congestion control schemes for DSRC-based CSA. A cross-layer design approach is used with congestion detection at the MAC layer and traffic rate control at the application layer. Simulation results show the effectiveness of the proposed rate control scheme for adapting to dynamic traffic loads.

Performance evaluation of distributed access scheme in error-prone channel

Distributed Coordination Function (DCF) protocol is used for channel access in IEEE 802.11 WLAN. The performance issue of the protocol has provoked a lot of research interest. However, during the previous research work, the impact of retransmissions and bit error ratio on the performance of DCF was not taken into consideration. An analytical model is presented in this paper to evaluate the performance of the scheme in the case of finite retransmissions.

Auction-based admission control and pricing for priority services

Priority queuing is often used as a way to provide differential services for users with different delay sensitivities. An auction-based admission control and pricing mechanism is proposed for priority services, where higher priority services are allocated to the users who are more sensitive to delay, and each user pays a congestion fee for the external effect caused by their participation. The mechanism is proved to be strategy-proof and efficient.

Investigation in subsequent request problem in probe-based multicast admission control scheme

Multicast is an efficient approach to save network bandwidth for multimedia streaming services. To guarantee QoS for multimedia streaming services, while maintain the bandwidth efficiency of the multicast transmission, admission control is expected. In this paper, we study a probe-based multicast admission control (PBMAC) scheme, which was proposed to provide scalable and simple admission control for multicast services. It is observed that, in the scheme, a so-called subsequent request problem degrades system performance significantly when the network traffic is heavily loaded. An analytical model of subsequent requests problem is provided in this paper. Based on the analysis, an enhanced PBMAC (EPBMAC) scheme is devised to solve the problem. A new metric - normalized requested equivalent link capacity is defined to evaluate the performance of both PBMAC and EPBMAC. Simulation results validate the analytical models for PBMAC and EPBMAC. Analytical and simulation results show that the subsequent request problem is well solved with minor assistance from routers.

Congestion pricing by priority auction

This paper analyzes a communication network facing users with a continuous distribution of delay cost per unit time. Priority queueing is often used as a way to provide differential services for users with different delay sensitivities. Delay is a key dimension of network service quality, so priority is a valuable resource which is limited and should to be optimally allocated. We investigate the allocation of priority in queues via a simple bidding mechanism. In our mechanism, arriving users can decide not to enter the network at all or submit an announced delay sensitive value. User entering the network obtains priority over all users who make lower bids, and is charged by a payment function which is designed following an exclusion compensation principle. The payment function is proved to be incentive compatible, so the equilibrium bidding behavior leads to the implementation of “cμ-rule”. Social warfare or revenue maximizing by appropriately setting the reserve payment is also analyzed.

Investigation on probing schemes in probe-based multicast admission control

Multicast is an efficient approach to save network bandwidth for multimedia streaming services. To provide Quality of Services (QoS) for the multimedia services while maintain the advantage of multicast in bandwidth efficiency, admission control for multicast sessions are expected. Probe-based multicast admission control (PBMAC) schemes are of a sort of scalable and simple admission control for multicast. Probing scheme is the essence of PBMAC. In this paper, after a detailed survey on three existing probing schemes, we evaluate these schemes using simulation and analysis approaches in two aspects: admission correctness and group scalability. Admission correctness of the schemes is compared by simulation investigation. Analytical models for group scalability are derived, and validated by simulation results. The evaluation results illustrate the advantages and weaknesses of each scheme, which are helpful for people to choose proper probing scheme for network.

An edge admission control scheme for multicast

Ensuring minimum quality-of-service levels to traffic flows and groups of flows is an important challenge for future packet networks. Admission control is an important measure for QoS provision. However, the problem of multicast admission control was much less investigated. In this paper, a reservation-based edge multicast admission control scheme is investigated, which targets high QoS level and scalability. Using a new concept, virtual link, a virtual-link-oriented quota-based resource management mechanism is proposed. Besides, a hierarchical distributed bandwidth broker architecture is also employed. In this scheme, a central bandwidth broker manages the physical link bandwidth, and allocates/reclaims the bandwidth to virtual links; edge bandwidth brokers manage the bandwidth of virtual links, make admission decisions and reserve bandwidth for each flow. Simulation results show that the scheme achieves high scalability. Furthermore, the impact of quota size on the performance and complexity is investigated. A bandwidth adaptive quota size scheme is proposed to further improve the performance and reduce the complexity.

An adaptive scheduling scheme for fair bandwidth allocation

Class-based service differentiation is provided in DiffServ networks. However, this differentiation will be disordered under dynamic traffic loads due to the fixed weighted scheduling. An adaptive weighted scheduling scheme is proposed in this paper to achieve fair bandwidth allocation among different service classes. In this scheme, the number of active flows and the subscribed bandwidth are estimated based on the measurement of local queue metrics, then the scheduling weights of each service class are adjusted for the per-flow fairness of excess bandwidth allocation. This adaptive scheme can be combined with any weighted scheduling algorithm. Simulation results show that, comparing with fixed weighted scheduling, it effectively improve the fairness of excess bandwidth allocation.

Revenue-maximizing pricing and resource allocation of differentiated services

The introduction of service differentiation in communication networks needs a multi-tiered pricing structure. In this paper, we analyze a communication network providing differentiated services for heterogeneous users by Paris Metro Pricing scheme, which is a very simple scheme to provide differentiated services. Basing on modeling strategies of users and the service provider, we answer the important question: how should the service provider optimally set prices and allocate resources for different services to maximize its revenue of overall services. To simplify the analysis the problem is firstly solved on the assumption that services are implicitly supplied, and then we extend the solution into a more realistic situation where services are explicitly supplied.

Quality of services support for IEEE 802.11 WLAN

As the channel is accessed randomly in IEEE 802.11 WLAN systems, it’s difficult to support Quality of Services for real time applications. To solve the issue, there are already some approaches proposed in different network layers. However, when those QoS approaches are implemented in different network environments, the performance may vary significantly. In this paper, we will compare two major classes of QoS schemes for IEEE 802.11 WLAN in MAC layer and network layer respectively. The performances are compared in both one hop and multi-hop ad hoc network environments. It’s observed that MAC layer QoS scheme is very efficient in one hop network environments, while network layer QoS schemes is only efficient for multi-hop ad hoc networks. Based on the observations, it’s necessary to design a new hybrid scheme to efficiently support QoS in IEEE 802.11 WLAN system.