Electronics Engineers. Wireless technologies in the LAN environment are becoming increasingly important and the IEEE 802.11 is the most mature technology to date. Previous works have pointed out that the standard protocol can be very inefficient and that an appropriate tuning of its congestion control mechanism (i.e., the backoff algorithm) can drive the IEEE 802.11 protocol close to its optimal behavior. To perform this tuning, a station must have exact knowledge of the network contention level; unfortunately, in a real case, a station cannot have exact knowledge of the network contention level (i.e., number of active stations and length of the message transmitted on the channel), but it, at most, can estimate it. This paper presents and evaluates a distributed mechanism for contention control in IEEE 802.11 Wireless LANs. Our mechanism, named Asymptotically Optimal Backoff (AOB), dynamically adapts the backoff window size to the current network contention level and guarantees that an IEEE 802.11 WLAN asymptotically achieves its optimal channel utilization. The AOB mechanism measures the network contention level by using two simple estimates: the slot utilization and the average size of transmitted frames. These estimates are simple and can be obtained by exploiting information that is already available in the standard protocol. AOB can be used to extend the standard 802.11 access mechanism without requiring any additional hardware. The performance of the IEEE 802.11 protocol, with and without the AOB mechanism, is investigated in the paper through simulation. Simulation results indicate that our mechanism is very effective, robust, and has traffic differentiation potentialities. Index Terms—Wireless LAN (WLAN), IEEE 802.11, multiple access protocol (MAC), protocol capacity, performance analysis. 1

Many new routing and MAC layer protocols have been proposed for wireless sensor networks tackling the issues raised by the resource constrained unattended sensor nodes in large-scale deployments. The majority of these protocols considered energy efficiency as the main objective and assumed data traffic with unconstrained delivery requirements. However, the growing interest in applications that demand certain end-toend performance guarantees and the introduction of imaging and video sensors have posed additional challenges. Transmission of data in such cases requires both energy and QoS aware network management in order to ensure efficient usage of the sensor resources and effective access to the gathered measurements. In this paper, we highlight the architectural and operational challenges of handling of QoS traffic in sensor networks. We report on progress make to-date and outline open research problems.

This paper examines a new mechanism for distributed resource reservation that offers support for applications with QoS requirements in a wireless multi-hop network. This mechanism is based on IEEE 802.11 DCF and includes end-to-end reservations of time slots and distribution of reservation information to mobile nodes unaware of the reservation, piggy-backed on existing medium access control messages.

Supporting applications with high quality-of-service requirements in wireless multihop networks is challenging, mainly due to uncertainties about the packet forwarding times introduced by the data link layer at every node on the path to the destination.

Abstract — This article presents an end-to-end reservation protocol

The ad hoc model has generated significant interest in the field of wireless (mobile and otherwise) networks in recent times. In the ad hoc model, the relationship between nodes that form a network are not fixed or predetermined, but rather the nodes communicate within themselves to "discover" the network configuration. Battery power conservation is of prime importance in such networks and is integral to problem areas such as routing, localization and management. Often the single largest energy expenditure is due to the wireless transceiver. In fixed wireless broadband networks, many times the wireless connections are point to point using a directional antenna. In ad hoc networks, most of the times a transmission by a node is targeted toward another specific node. In such a case, power is wasted by using a broadcast instead of a directional transmission. If the ad hoc network runs a localization algorithm and if a directional antenna is available, a focused beam may be used. Other transmissions may need to be broadcast because the location of the receiving node(s) may not be known. We propose a tandem scheme of using both broadcast and directional transmissions to optimize the use of battery power. In addition to studying the case for a specific network architecture of our own choice, we define a mathematical framework for quantifying the applicability of similar tandem schemes in various ad hoc architectures.

Abstract: A network model is proposed to support service differentiation for mobile Ad Hoc networks by combining a fully distributed admission control approach and the DIFS based differentiation mechanism of IEEE802.11. It can provide different kinds of QoS (Quality of Service) for various applications. Admission controllers determine a committed bandwidth based on the reserved bandwidth of flows and the source utilization of networks. Packets are marked when entering into networks by markers according to the committed rate. By the mark in the packet header, intermediate nodes handle the received packets in different manners to provide applications with the QoS corresponding to the pre-negotiated profile. Extensive simulation experiments showed that the proposed mechanism can provide QoS guarantee to assured service traffic and increase the channel utilization of networks.

The fast development wireless networks have been experiencing recently offers a set of different possibilities for mobile users, that are bringing us closer to voice and data communications “anytime and anywhere”. Some outstanding solutions in this field are Wireless Local Area Networks, that offer high-speed data rate in small areas, and Wireless Wide Area Networks, that allow a greater mobility for users. In some situations, like in military environment and emergency and rescue operations, the necessity of establishing dynamic communications with no reliance on any kind of infrastructure is essential. Then, the ease of quick deployment ad hoc networks provide becomes of great usefulness. Ad hoc networks are formed by mobile hosts that cooperate with each other in a distributed way for the transmissions of packets over wireless links, their routing, and to manage the network itself. Their features condition their design in several network layers, so that parameters like bandwidth or energy consumption, that appear critical in a multi-layer design, must be carefully taken into account. This work, with the aim of identifying open questions and research problems, is a literature survey on ad hoc networks that addresses some of their critical design

Abstract — IEEE 802.11 has become de facto standard for wireless LANs. Although it was originally designed for data communication, emergence of Voice over IP (VoIP) has made it attractive for voice applications. But voice applications require delay guarantee. We have implemented Dynamic Class Selection (DCS) mechanism in Neighborhood Proportional Delay Differentiation (NPDD) (proposed in [1]) architecture to provide delay assurance in IEEE 802.11 networks. But we found that DCS is not suitable for voice applications which require tight delay bound. Hence, we propose two Adaptive Class Selection (ACS) mechanisms to provide delay assurances to voice flows. However, delay assurance at all nodes within a LAN cannot be provided with ACS or DCS. So we propose Measurement based Distributed Call Admission Control (MDAC) mechanism to provide delay assurances for voice traffic at all nodes. Our experimental results show that ACS and MDAC perform much better than DCS for voice flows at all loads. I.

Abstract: To support multimedia applications, it is desirable that an ad hoc network has a provision of Quality of Service (QoS). However, the provision of QoS in a mobile ad hoc network is a challenging task. In this paper, we present a review of the current research related to the provision of QoS in an ad hoc environment. We examine issues and challenges involved in providing QoS in an ad hoc network. We discuss methods of QoS provisioning at different levels including those at the levels of routing, Medium Access Control (MAC), and cross layer. Also, we discuss schemes for admission control and scheduling that are proposed in the literature for the provision of QoS. We compare salient features of various solutions and approaches and point out directions for future work.