This paper proposes a MAC protocol for presence information discovery in ubiquitous networks. The proposed protocol is designed for proactive discovery in which wireless devices periodically broadcast packets containing presence information. The protocol is based on Framed Aloha. The objective of the protocol is to assure the discovery time of single-hop neighbors considering wireless collisions and also power consumption. In this paper, we show that the proposed protocol is able to assure specified discovery time in distributed networks with random topology.

We propose a medium access control (MAC) protocol for real-time applications in one-hop ad-hoc wireless networks. It is a distributed mechanism that takes account of priority and has a bounded packet delay. Nodes use energy signals to contend for the right to access the channel. Nodes, which have a packet to transmit, send energy signals or listen to the channel based on their binary frame. The node that has sent energy signals and has not heard any energy signals wins the right to access the channel. We use two schemes to determine the binary frame: at the beginning of a session, a node determines it based on its priority level and a random number; after successful transmission, based on a count of successful packet transmissions. With the first scheme, in order to reduce contention losses, the nodes that had won the right to access the channel but failed in transmission have priority over the other nodes. With the second scheme, the node that has the largest count, the one that has been waiting the longest, can send a packet without risking collision. The protocol provides higher probability of successful transmission and a limit on maximum packet delay. An analysis of the protocol provides conditions for the protocol to be stable. We evaluate the performance of the proposed protocol using simulations of a network with a mixed population of data and real-time nodes, whose source is constant bit rate (CBR) and a two state Markov on/off process.

We analyze the energy consumption of the sensor-medium access control (S-MAC) protocol, where contending nodes exist. Because all nodes running the S-MAC within a virtual cluster always behave with a fixed frame length, the behavior should be analyzed based on its frame. Hence, reflecting the frame architecture, we first present an analytic model for the S-MAC behavior with a discrete-time Markov chain, and then we analyze energy consumption under unsaturated conditions.

In this paper a multi-channel MAC protocol with dynamic channel allocation (MMAC-DCA) in CDMA Ad Hoc networks is proposed. Under MMAC-DCA, the service sub-channels are dynamically allocated by the RTS/CTS dialogue on the common sub-channel, only when a node has a packet to transmit. In addition, a Markov mode is presented to analyze the performance of MMAC-DCA.

This paper addresses the issue of deafness in MAC (Medium Access Control) protocols for wireless ad hoc networks using directional antennas. Directional antennas are expected to provide significant improvements over omni-directional antennas in ad hoc networks, such as high spatial reuse and range extension. Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for ad hoc networks. However, directional MAC protocols inherently introduce new kinds of problems arising from directivity. One major problem is deafness, caused by a lack of state information of neighbor nodes, whether idle or busy. This paper proposes DMAC/DA (Directional MAC with Deafness Avoidance) to overcome the deafness problem. DMAC/DA modifies the previously proposed MAC protocol, MDA (MAC protocol for Directional Antennas), to reduce the number of control messages and also maintain the ability to handle deafness. In DMAC/DA, WTS (Wait To Send) frames are simultaneously transmitted by the transmitter and the receiver after the successful exchange of directional RTS (Request To Send) and CTS (Clear To Send) to notify the on-going communication to potential transmitters that may experience deafness. The experimental results show that DMAC/DA outperforms existing directional MAC protocols, such as DMAC (Directional MAC) and MDA, in terms of throughput, control overhead and packet drop ratio under the different values of parameters such as the number of flows and the number of beams. In addition, qualitative evaluation of 9 MAC protocols is presented to highlight the difference between DMAC/DA and existing MAC protocols.

In this paper, we propose TB-MAC (Threshold-Based MAC), which has been designed to consider various network traffic conditions while providing energy efficiency in a wireless sensor networks. Existing MAC protocols for sensor networks attempt to solve the energy consumption problem caused by idle listening using an active/sleep duty cycle. Since there are various traffic conditions, however, they may not always provide improvements in energy consumption. Hence, we propose a MAC protocol algorithm that stores data in a buffer and transmits data when the buffer exceeds a threshold value so that energy efficiency is always guaranteed for any network traffic condition. The analytical results show that our proposed algorithm enables significant improvements in energy consumption compared to the existing MAC protocols for sensor networks.

Multimedia Wavelength Division Multiple Access (M-WDMA) specially designed to accommodate multimedia traffic is a well-known media access control (MAC) protocol. This paper extensively analyzes the throughput of M-WDMA. Specifically, this analysis considers a wide range of network conditions including varying traffic loads, probabilistic occupancy of time segment, various traffic distribution patterns (TDPs) and channel sharing methods (CSMs) under both symmetric and asymmetric traffic load patterns (TLPs). Thus, the analytic behavior of M-WDMA can be investigated for designing a WDMA network managing multimedia traffic under practical environments.

The medium access control (MAC) protocol is the main determiner of the system throughput in Wireless Local Area Networks (WLANs). The MAC technique of the IEEE 802.11 protocol is called Distributed Coordination Function (DCF). DCF is based on a carrier sense multiple access with collision avoidance (CSMA/CA) scheme with binary slotted exponential backoff. Each station generates a random backoff interval before transmitting a packet to minimize the probability of collision with packets being transmitted by other stations. However, when the number of stations increases, the system throughput decreases. This paper proposes a new backoff algorithm that uses finish tags. The proposed algorithm uses the finish tag of each station to control the backoff intervals so as to improve system throughput. The finish tag is updated when a packet reaches the front of its flow, and it is attached to the packet just prior to transmission. When a station receives packets with older finish tags, its backoff time interval is increased. For this reason, the more the stations there are, the larger the backoff time becomes. Simulations confirm that the proposal improves system throughput of a IEEE 802.11 network under saturation conditions.

When digital broadcasting services are provided through cable television (CATV) networks, viewers watching interactive programs such as quizzes or auctions may respond to the program within a short period. If these responses are transmitted in the upstream channel of the CATV networks using TCP/IP, they will result in burst traffic. The numerous TCP connections will trigger congestion in the upstream transmission facilities and will cause a significant delay in conventional Internet services such as web-browsing. The present paper proposes a new method of controlling the CATV upstream channel to avoid such congestion. We introduce class-based queues at each cable TV station, in which each service class is related to a type of interactive service. The status of the queue is relayed to the cable modems of subscribers using a CATV-specific MAC protocol. This queue-status information is used to suspend further initiation of TCP connections at cable modems. As a result, the TCP connections will be arbitrated in the CATV network, while the delay of the response transmission is traded for smoothing of the burst traffic. We numerically evaluate the effect of the proposed method using the time distribution of responses to an actual quiz program. The results show that the proposed method successfully suppresses interference of the burst traffic with conventional best-effort services.

TCP performance in the IEEE 802.11-based multihop ad hoc networks is extremely poor, because the congestion control mechanism of TCP cannot effectively deal with the problem of packet drops caused by mobility and shared channel contention among wireless nodes. In this paper, we present a cross-layer method, which adaptively adjusts the TCP maximum window size according to the number of RTS (Request To Send) retry counts of the MAC layer at the TCP sender, to control the number of TCP packets in the network and thus decrease the channel contention. Our simulation results show that this method can remarkably improve TCP throughput and its stability.

This paper introduces 12 channel reservation techniques for medium access control (MAC) protocols suitable for high bit-rate wireless communication systems. The first 7 algorithms, namely CFP, CAP, COP, COP+SPL, CFP+SPL, UNI and UNI+LA, are applicable to systems with single-access chance per frame, whereas the other 5 algorithms, namely MT-CFP, MT-CFP+SPL, MT-UNI, MT-UNI+LUA and MT-UNI+LUT are suitable for systems with multi-access attempts per frame. The performance of these techniques are analytically evaluated and compared with the existing known techniques. The analytical model derived here are also validated through Monte Carlo computer simulations. Numerical results show that all proposed techniques are in general more superior to conventional reservation techniques. Finally when comparing between all proposed schemes in terms of both throughput performance and practical feasibility it is found that the MT-UNI+LA scheme are relatively efficient and suitable for practical applications.

Use of directional antenna in the context of ad hoc wireless networks can largely reduce radio interference, thereby improving the utilization of wireless medium. Our major contribution in this paper is to devise a MAC protocol that exploits the advantages of directional antenna in ad hoc networks for improved system performance. In this paper, we have illustrated a MAC protocol for ad hoc networks using directional antenna with the objective of effective utilization of the shared wireless medium. In order to implement effective MAC protocol in this context, a node should know how to set its transmission direction to transmit a packet to its neighbors and to avoid transmission in other directions where data communications are already in progress. In this paper, we are proposing a receiver-centric approach for location tracking and MAC protocol, so that, nodes become aware of its neighborhood and also the direction of the nodes for communicating directionally. A node develops its location-awareness from these neighborhood-awareness and direction-awareness. In this context, researchers usually assume that the gain of directional antennas is equal to the gain of corresponding omni-directional antenna. However, for a given amount of input power, the range R with directional antenna will be much larger than that using omni-directional antenna. In this paper, we also propose a two level transmit power control mechanism in order to approximately equalize the transmission range R of an antenna operating at omni-directional and directional mode. This will not only improve medium utilization but also help to conserve the power of the transmitting node during directional transmission. Our proposed directional MAC protocol can be effective in both ITS (Intelligent Transportation System), which we simulate in String and Parallel Topology, and in any community network, which we simulate in Random Topology. The performance evaluation on QualNet network simulator clearly indicates the efficiency of our protocol.

Wireless local area networks, in which every station can transmit via any one of the available operating channels, but only one channel at a time, are investigated. Two distributed random access protocols are proposed for these WLANs. The CSMA/CA protocol is similar to the IEEE 802.11 standard but with slight modifications for multiple operating channels. The fuzzy logic controlled protocol employs a simple fuzzy logic controller to tune the size of backoff window. Extensive simulations are provided to evaluate the channel utilization, fairness, and responsiveness of these two protocols. Furthermore, the effects of employing RTS/CTS mechanism with both protocols are considered. Finally, performances of these two protocols are also investigated under conditions of burst traffic and noisy channels. Simulation results show that the fuzzy logic controlled protocol is a great improvement of the CSMA/CA protocol.

The unfairness problem among TCP connections has been proved to be very severe in the IEEE 802.11-based wireless ad hoc networks because the hidden station problem still exists and the binary exponential backoff algorithm always favors the latest successful station. In this paper, a novel protocol, neighbor-medium-aware MAC (NEMA-MAC), is proposed to improve the TCP fairness. By adding a medium (channel) state field in the head of the traditional IEEE 802.11 MAC frame, the NEMA-MAC protocol provides a communication mechanism to resolve the hidden station problem. In addition, when a collision occurs, the new backoff algorithm makes the senders cooperatively adjust the contention window according to their local and neighbors' channel usage indexes. The simulation results show that TCP sessions can acquire satisfying fairness and increase the throughput in the NEMA-MAC-based multihop ad hoc networks.

In this paper, a contention-based reservation MAC protocol is proposed for non-real-time burst traffic class in wireless ATM networks. The proposed protocol is characterized by the contention-based transmission of the reservation request and contention-free transmission of burst traffic. The design objective of the proposed protocol is to reduce contention delay during the contention phase of a connection. In order to reduce collision of reservation requests, the base station calculates the transmission probability based on the estimated load of reservation requests and the number of random access minislots, and broadcasts it over the frame header period of downlink channel. Wireless terminal, which has traffic burst, selects a random access minislot and transmits its reservation request with a received transmission probability. Based on the successfully received reservation, the scheduler allocates the uplink data slots to wireless terminal. Simulation results show that the proposed protocol can provide higher channel utilization, and furthermore, maintains constant delay performance in a heavy traffic environment.

Future wireless communication systems will provide mobile terminals with high bit-rate transmissions for accessing broadband wired networks. In this paper, we envisage a Time Division Multiple Access - Time Division Duplexing (TDMA-TDD) air interface and we propose a Medium Access Control (MAC) protocol, named Dynamic Scheduling - TDD (DS-TDD), that allows guaranteeing the QoS of different traffic classes and efficiently supports uplink/downlink traffic asymmetries. The DS-TDD performance is theoretically analyzed. Moreover, the DS-TDD protocol is compared with another scheme proposed in the literature. Finally, the impact of packet errors on the DS-TDD performance is evaluated.

A new MAC protocol using the Adaptive Weighted Round Robin with Delay Tolerance (AWRR/DT) is presented. The proposed protocol is a type of centralized MAC protocol where the base station performs most operations. By using the AWRR/DT scheduler, we can guarantee delay QoS to different traffics without the heavy overhead induced by packet-based tagging techniques. In order to enhance the efficiency of random access systems, the proposed protocol employs three novel contention methods: slotted ALOHA with threshold, contention method using adaptive contention period, and traffic-specific contention method. Simulation results show that the proposed protocol guarantees delay bounds by using the AWRR/DT. The slotted ALOHA with threshold suffers less collisions than the regular slotted ALOHA when mobile terminals request slots. The method using adaptive contention period adjusts the length of contention period of each frame to relieve the performance degradation by collisions. The traffic-specific contention method provides a priority handling mechanism to contention-based systems. Experimental results of each contention method are provided.

Progress in the fields of broadband access networks and information appliances has led to the introduction of a new network domain called Home Network. In 1999, HomePNA 2.0 using phone lines was proposed, and we believe it is one of the most promising solutions, because of its cost-effectiveness. However, it is not able to guarantee the QoS due to the adaptation of the mature IEEE802.3 CSMA/CD technology which is used for Ethernet. In light of this, we propose and evaluate a new MAC protocol for the Home Network called the HomeMAC that provides guaranteed QoS for appliances and PCs. HomeMAC features a hybrid CSMA/CD-Timed Token protocol which combines the CSMA/CD with timed token protocol and transmits real-time traffic based on the QoS Level Table (QLT) for guaranteeing QoS. In the HomeMAC, there are two different transmission modes, namely, the CSMA/CD Mode when there is no real-time traffic, and the Timed Token Mode when there is real-time traffic taking place. By dynamically switching the transmission mode between CSMA/CD Mode and Timed Token Mode in accordance with the different kinds of traffic, the hybrid protocol provides low delay, low jitter, and low loss rate to multimedia appliances such as TVs, DVDs, and PCs. Moreover, by providing flexible bandwidth allocation based on QLT, the HomeMAC can serve high QoS whole covering entire offered load.

Progress in the field of broadband access network and information appliances has led to the advent of a new network field called Home Network. In 1999, HomePNA2.0 using phone line was proposed, and we believe that it is one of the most promising solutions because of its cost-effectiveness. However, due to adaptation of the mature IEEE802.3 CSMA/CD technology used for Ethernet, it is not able to guarantee the QoS. We present the design, implementation and empirical evaluation of a new MAC protocol for the Home Network called HomeMAC. In this paper, the software based HomeMAC is implemented by programming the kernel space of FreeBSD. HomeMAC features a hybrid CSMA/CD-Timed Token protocol which combines the CSMA/CD for non-real-time traffic with timed token protocol for real-time traffic. In addition, by providing flexible bandwidth allocation based on QoS Level Table (QLT), HomeMAC can serve high QoS covering the whole offered load. From the results of evaluation of software implementation, we verify that HomeMAC can provide low delay, low loss, and low jitter to the real-time traffic by reservation of the bandwidth.

In this paper, we propose a channel assignment scheme for integrated voice and data traffic in reservation multiple access protocol. In the proposed scheme, a voice packet never contends with a data packet and takes over the slot which is previously assigned to a data packet. Thus, a larger number of voice terminals can be accommodated without degradation of quality and throughput even in the situation that data were integrated. We evaluate the voice packet dropping probability, throughput and packet delay through computer simulation. The results show that the proposed scheme has better performance than the conventional PRMA and DQRUMA systems.