Multihop wireless hotspot network [A. Balachandran et al., (2003), F. Fitzek et al., (2003), Y-D. Lin et al., (1999), K-C. Wang et al., (2003)] has been recently proposed to extend the coverage area of a base station. However, with selfish nodes in the network, multihop packet forwarding cannot take place without an incentive mechanism. In this paper, we adopt the "pay for service" incentive model, i.e., clients pay the relaying nodes for their packet forwarding service. Our focus in this paper is to determine a "fair" pricing for packet forwarding. To this end, we model the system as a market where the pricing for packet forwarding is determined by demand and supply. Depending on the network communication scenario, the market models are different. We classify the network into four different scenarios and propose different pricing mechanisms for them. Our simulation results show that the pricing mechanisms are able to guide the market into an equilibrium state quickly. We also show that maintaining communication among the relaying nodes is important for a stable market pricing.

Providing service differentiation in wireless networks has attracted much attention in recent research. Existing studies so far have focused on the design of MAC layer protocols to achieve distributed priority scheduling. While these works have been shown to achieve certain differentiation (higher throughput or lower delay for higher priority packets) at MAC layer, they did not consider the problem of service differentiation from end-to-end perspective. Moreover, these approaches did not present a formalized service differentiation model that quantifies the degree of differentiation, which is critical for service class selection and provision. This paper addresses above problems by introducing a clear service differentiation model, proportional service differentiation, to the domain of wireless network which targets at providing proportional delay differentiation in wireless LAN. Due to the unique characteristic of distributed medium sharing, the scheduling algorithm employed in wireline networks can not be applied directly to the context of the wireless network. We argue that delay differentiation in wireless LAN can be only achieved through a joint packet scheduling at network layer and distributed coordination at MAC layer. Hereby, we present a distributed waiting time priority scheduling (DWTP) algorithm which is deployed on a cross-layer architecture. DWTP consists of two tiers: an intra-node predictive WTP scheduler at network layer and an inter-node priority-based distributed coordination at MAC layer. These two tiers coordinate via cross-layer priority mapping to achieve proportional delay differentiation. Simulation results show that the cross-layer DWTP algorithm can effectively achieve proportional delay differentiation in wireless LAN.

In a public mobile ad hoc network (MANET), users may be selfish and refuse to forward packets for other users. Therefore, an incentive mechanism must be in place. We adopt the "pay for service" model of cooperation, and propose an auction-based incentive scheme (called iPass) to enable cooperative packet forwarding behavior in MANET. Each flow pays the market price of packet forwarding service to the intermediate routers. The resource allocation mechanism in our scheme is based on the generalized Vickrey auction with reserve pricing. We prove that in our scheme, user's truthful bidding of utility remains a dominant strategy, users and routers have incentive to participate in the scheme, and packet forwarding always leads to higher social welfare for the whole network. We design a signaling protocol to implement the scheme, and show that it can serve as an explicit rate-based flow control mechanism for the network. Therefore, iPass is a joint solution of incentive engineering and flow control in a noncooperative MANET. Simulation results show that iPass is able to determine the auction outcome quickly, and at the same time achieve the goals of flow control.

Flow control in a mobile ad hoc network (MANET) must face many new challenges such as frequent rerouting and bandwidth variation of the wireless links. TCP's implicit AIMD flow control performs poorly in this environment, because it often cannot keep up with the dynamics of the network. This paper explores the potential utility of explicit flow control in the MANET domain. To this end, we propose an end-to-end rate-based flow control scheme (called EXACT), where a flow's allowed rate is explicitly conveyed from intermediate routers to the end-hosts in each data packet's special control header. As a result, EXACT reacts quickly and precisely to re-routing and bandwidth variation, which makes it especially suitable for a dynamic MANET network and also discusses several supporting mechanisms required for such a scheme at the MAC and the transport layers. By ns-2 simulations, we show that EXACT outperforms TCP in terms of fairness and efficiency, especially in a highly dynamic MANET environment.

Abstract Providing service differentiation in wireless networks has attracted much attention in recent research. Existing studies so far have focused on the design of differentiated media access algorithms. Some quality of service (QoS) metrics, such as queueing delay cannot be completely addressed by these approaches. Moreover, without a formalized service differentiation goal that quantifies the outcome of differentiation, the performance of most of the approaches fluctuates, especially in short time‐scales. This paper addresses above problems by introducing the concept of proportional service differentiation, to the domain of wireless network and focuses on providing proportional delay differentiation in wireless LANs. Due to the unique characteristic of distributed medium sharing, the scheduling algorithm employed in wireline networks can not be applied directly to the context of wireless LANs. We argue that delay differentiation in wireless LAN can only be achieved through a joint packet scheduling at the network layer and distributed coordination at the media access control (MAC) layer. Therefore, we present a cross‐layer waiting time priority (CWTP) scheduling algorithm. CWTP consists of two tiers: an intra‐node waiting time priority (WTP) scheduler at the network layer and an inter‐node distributed coordination function at the MAC layer. These two tiers coordinateviaa mapping function, which maps the normalized waiting time at the network layer to the backoff time at the MAC layer. Two mapping schemes, namely linear mapping and piecewise linear mapping, are presented and evaluated in this paper. Extensive simulation results show that the CWTP algorithm can effectively achieve proportional delay differentiation in wireless LANs. Copyright © 2004 John Wiley & Sons, Ltd.

Improving TCP performance has long been the focus of many research efforts in mobile ad hoc networks (MANET). In this paper, we address one aspect of this endeavor: how to properly set TCP's congestion window limit (CWL) to achieve optimal performance. Past research has shown that using a small CWL improves TCP performance in certain scenarios [M. Gerla et al., Feb. 1999], [Z. Fu et al., Apr. 2003], however, no comprehensive study has been given. To this end, we turn the problem of setting TCP's optimal CWL into identifying the bandwidth-delay product (BDP) of a path in MANET. We first show and prove that, independent of the MAC layer protocol being used, the BDP of a path in MANET cannot exceed the round-trip hop-count (RTHC) of the path. We further refine this upper bound based on the IEEE 802.11 MAC layer protocol, and show that in a chain topology, a tighter upper bound exists, which is approximately 1/5 of the RTHC of the path. Based on this tighter bound, we propose an adaptive CWL setting strategy to dynamically adjust TCP's CWL according to the current RTHC of its path. Using ns-2 simulations, we show that our simple strategy improves TCP performance by 8% to 16% in a dynamic MANET environment.

Distributed weighted fair scheduling schemes for QoS support in wireless networks have not yet become standard. In this paper we propose an admission control and dynamic bandwidth management scheme that provides fairness in the absence of distributed link level weighted fair scheduling. In case weighted fair scheduling becomes available, our system assists it by supplying the scheduler with weights and adjusting them dynamically as network and traffic characteristics vary. To obtain these weights, we convert the bandwidth requirement of the application into a channel time requirement. Our bandwidth manager then allots each flow a share of the channel time depending on its requirement relative to the requirements of other flows in the network. It uses a max-min fairness algorithm with minimum guarantees. The flow controls its packet transmission rate so it only occupies the channel for the fraction of time allotted to it by the bandwidth manager. As available bandwidth in the network and the traffic characteristics of various flows change, the channel time proportion allotted also dynamically varies. Our experiments show that, at the cost of a very low overhead, there is a high probability that every flow in the network will receive at least its minimum requested share of the network bandwidth.

Group communication has become increasingly important in mobile ad hoc networks (MANET). Current multicast routing protocols in MANET have a large overhead due to the dynamic network topology. To overcome this problem, there is a recent shift towards stateless multicast in small groups. We introduce a small group multicast scheme, based on packet encapsulation, which uses a novel packet distribution tree construction algorithms for efficient data delivery. The tree is constructed with the goal of minimizing the overall bandwidth cost of the tree. Two construction algorithms, for a location-guided k-ary (LGK) tree and a location-guided Steiner (LGS) tree, utilize the geometric locations of the destination nodes as heuristics to compute the trees. They are accompanied by a hybrid location update mechanism to disseminate location information among a group of nodes. Our simulation results show that LGS tree has lower bandwidth cost than LGK tree when the location information of the nodes is up-to-date, and its cost is similar to that of an optimal Steiner multicast tree. When location information of the nodes is out-dated, LGK tree outperforms LGS tree due to its lower computational complexity.