MAC Layer

To improve the MAC efficiency of each single link transmission, frame aggregation [7], is proposed in IEEE 802.11n to reduce contention by aggregating multiple frames for the same destination together at MAC layer. The applications of MAC frame aggregation are limited to bulk transmissions as the sender needs to wait to collect enough payloads before actual transmission, and thus it is not applicable to real-time applications like VoIP and other short data flows such as short HTTP transactions. Although the multi-user frame aggregation can be achieved at MAC layer, it suffers from the many limitations in large audience environments. There are a bundle of active STAs associated with one AP in large audience environments. Explicitly indicating each receiver’s MAC address at header would incur substantial overhead, which compromises the transmission efficiency.

Present days, the IEEE 802.11 wireless local area network technology offers the most important deployed wireless access to the web. This technology specifies each the Medium Access management (MAC) and also the Physical Layers (PHY). The PHY layer selects the proper modulation theme given the channel conditions and provides the mandatory information measure, whereas the mac layer decides in a very distributed manner on however the offered information measure is shared among all stations (STAs). This normal permits a similar mac layer to control on prime of 1 of many PHY layers. This model has completely different extensions on that I'm acting on. One extension considers Associate in Nursing Access purpose (AP) that transmits packets, which might permit finding the best Access purpose placement for a given topology. There are varied makes an attempt to model and analyze the saturation outturn and delay of the IEEE 802.11 mac layer.

All the calculi mentioned up to now abstract away from the from the possibility of interference between broadcasts. Lanese and Sangiorgi [24] have instead proposed the CWS calculus, a lower level untimed calculus to describe interferences in wireless systems. In their operational semantics there is a separation between the beginning and ending of a broadcast, so there is some implicit representation of the passage of time. A more explicit timed generalisation of CWS is given [29] to express MAC-layer protocols such as CSMA / CA, where the authors propose a bisimilarity which is proved to be sound but not complete with respect to a notion of reduction barbed congruence. We view the current paper as a simplification and generalisation of [29].

MANET is a self-organizing system of mobile nodes that can be connected by wireless links on an ad hoc basis. In a MANET, the nodes are free to move randomly, causing the network’s topology to change dynamically. Their high mobility and ad hoc nature poses greater security threats. Moreover, because they do not have a centralized controlling entity, it may be advantageous for individual nodes not to cooperate. Misbehavior of nodes can be commonly found in either forwarding or routing. Among these, timing attack at the MAC layer leads to serious consequences such as violation of QoS. Reputation systems can handle such kind of misbehavior that is observable. This paper proposes a MAC Layer based Reputation System for MANETs. It incorporates misbehavior observation, statistical calculation of reputation index, diagnosis and mitigation. The proposed model is implemented with modifications in the MAC component of ns2 and the results are compared with the existing MAC protocol. Result shows that the proposed model enhances the network performance by reducing the number of packet drops by 11% and increasing the throughput in the network by 23%.

As a condition to accessing the medium, the MAC Layer checks the value of its network allocation vector (NAV), which is a counter resident at each station that represents the amount of time that the previous frame needs to send its frame. The NAV must be zero before a station can attempt to send a frame. Prior to transmitting a frame, a station calculates the amount of time necessary to send the frame based on the frame's length and data rate. The station places a value representing this time in the duration field in the header of the frame. When stations receive the frame, they examine this duration field value and use it as the basis for setting their corresponding NAVs. This process reserves the medium for the sending station.

IEEE 802.15.4 protocol works to specify the physical and MAC sub-layer of LR-WPAN (Low Rate Wireless Personal Area Network) [2]. Although this is the standard protocol that was initially not developed for usage in WSNs, it provides enough flexibility that suits the requirements of WSNs by tuning its parameters as per requirement. In fact, low-rate, low-power consumption and low-cost wireless networking are the key features of the IEEE 802.15.4 protocol [3], which fulfills the basic requirements of WSNs. In this protocol, the physical layer is developed low data-rates, energy efficiency, and robustness, whereas, MAC layer which contains the superframes structure, provides the flexibility to meet the requirements of the other applications. The IEEE 802.15.4 protocol has attracted several recent research works.

MAC layer jamming is a common attack on wireless networks, which is easy to launch by the attacker and which is very effective in disrupting the service provided by the network. Most of the current MAC protocols for wireless networks, for example, IEEE 802.11, do not provide sufficient protection against MAC layer jamming attacks. In this paper, we first use a non-cooperative game model to characterize the interactions among a group of self-interested regular users and a malicious user. It can be shown that the Nash equilibrium of this game is either inefficient or unfair for the regular users. We introduce a policer (an intervention user) who uses an intervention function to transform the original non-cooperative game into a new non-cooperative game augmented by the intervention function, in which the users will adjust to play a Nash equilibrium of the augmented game. By properly designing the intervention function, we show that the intervention user can effectively mitigate the jamming attacks from the malicious user, and at the same time let the regular users choose more efficient transmission strategies. It is proved that any feasible point in the rate region can be achieved as a Nash equilibrium of the augmented game by appropriately designing the intervention.

main factors, which are: 1) the fact that many of the devices in M2M networks are expected to be battery operated and thus power constrained; 2) the economic impact (such as operational costs and profit margins) of the power consumed by the communication infrastructure; and 3) the environmental impact of the power consumed. The information and communications industry is currently responsible for 1.3% of total harmful emissions in the world [5]. This number is relied upon to increment with the blast of M2M gadgets in the coming decade. Considering each of the three components, it is hence basic that all operations related with M2M communications be upgraded to devour low power. For the battery operated M2M devices, two major supporters of force utilization are the vitality spent on the radio transmissions and the channel access. Crashes amid channel access are a noteworthy reason for force utilization that ought to be diminished to the best degree conceivable, just like the force devoured because of the transmission of control data. For example, at high loads, the control overhead may consume almost 50% of the total energy in the IEEE 802.11 MAC protocol [1]. Basic strategies to diminish the MAC layer vitality utilization incorporate lessening the impacts, rest planning, power control, and decreasing unmoving tuning in.

Mobile Ad hoc Networks is a collection of autonomous mobile nodes that are dynamically communicating without any centralized administration. It is a self-creating, self-arrange and self-regulating network. In this network each node plays dual role i.e., node as well as router. In Mobile ad hoc network, nodes are having high mobility; because of this mobility routing is an important issue in Ad hoc network. An efficient routing protocol, which provides QoS by minimizing delay and power consumption while maximizing throughput and utilization of resources, remains a challenge issue for the ad- hoc network. MAC layer plays key role in Routing, so the selection of routing protocols and impact of MAC layer on routing protocols is one of the research areas in MANETs.

We set out to analyze the 802.11e MAC protocol. We realize that an analysis of the exact scheme is cumber- some. We thus propose a hybrid-MAC model that resembles the 802.11e MAC in most essential respects. Our MAC model provides us with an abstraction of the essential features of 802.11e MAC, while avoiding the complex details of the latter. We believe that the insights obtained using our model are applicable to the 802.11e scenario. Our system model can be thought of as a hybrid MAC model which operates in both the contention and CFPs alternately, akin to a legacy 802.11 MAC protocol [4] with both its (a) distributed coordina- tion function (DCF) and (b) point coordination function (PCF) modes enabled [4]. While DCF is based on the contention-based CSMA/CA mode of channel access, PCF is based on the polling mechanism. Limited QoS support in the legacy 802.11 standard is available through the use of the PCF. The DCF phase mimics the enhanced distributed channel access (EDCA) mechan- ism which is a contention-based channel access scheme while the PCF mimics the HCCA which is based on a

Sensor-MAC (S-MAC) locally managed synchronizations and periodic sleep listen schedules based on these synchronizations form the basic idea behind the Sensor-MAC (S-MAC) protocol [5]. Neighboring nodes form virtual clusters to set up a common sleep schedule. If two neighboring nodes reside in two different virtual clusters, they wake up at listen periods of both clusters. A drawback of S-MAC algorithm is this possibility of following two different schedules, which results in more energy consumption via idle listening and overhearing. Schedule exchanges are accomplished by periodical SYNC packet broadcasts to immediate neighbors. The period for each node to send a SYNC packet is called the synchronization period. Figure 1 represents a sample sender-receiver communication. Collision avoidance is achieved by a carrier sense, which is represented as CS in the figure. Furthermore, RTS/CTS packet exchanges are used for uncast type data packets. An important feature of S-MAC is the concept of message-passing where long messages are divided into frames and sent in a burst. With this technique, one may achieve energy savings by minimizing communication overhead at the expense of unfairness in medium access. Periodic sleep may result in high latency especially for multi-hop routing algorithms, since all immediate nodes have their own sleep schedules. The latency caused by periodic sleeping is called sleep delay in [1]. Adaptive listening technique is proposed to improve the sleep delay, and thus the overall latency. In that technique, the node who overhears its neighbor‟s transmissions wakes up for a short time at the end of the transmission. Hence, if the node is the next- hop node, its neighbor could pass data immediately. The end of the transmissions is known by the duration field of RTS/CTS packets.

Current deployments of mesh networks like e.g. Roofnet [3] are typically based on a single radio technology, generally IEEE 802.11 [4], due to its low cost and use of unlicensed spectrum. Despite the benefits in terms of management, choosing a single technology pre- vents an efficient and cost-effective deployment, as the suitability of radio technology heavily depends on the particular scenario in terms of user density, physical distances, traffic char- acteristics, etc. However, supporting different radio technology interfaces may introduce a high management burden, severely reducing the benefits of a mesh network approach. In this paper we present an architecture that tackles this technical challenge by designing an abstrac- tion layer to hide most of the complexity of the radio interface management. This architecture is being developed by the CARMEN (CARrier grade MESh Networks) project.

To obtain network address, there are three topological parameters to be defined: the number of child devices (Cm), the network maximum depth value (Lm) and the maximum [r]

Hybrid multichannel MAC protocol for the vehicular network. This protocol enhanced the throughput and reduces the collision on the network. The co-ordination between the nodes is nontrivial and it supports TDMA and CSMA to improve the reliability in broadcasting messages. This protocol controls the undesired messages and eliminates them. It works on the approach of time slot division and provides faster services [3]. The result of the proposed method shows that this method reduces collision level and enhanced the throughput of the network [4].

In this section, we show how our calculus CCCP can be used to model different interesting beha- viours which arise at the MAC sub-layer [26] of wireless networks. Then, we exploit our bisimu- lation proof technique to provide examples of behaviourally equivalent networks. In particular we give some examples comparing the behaviour of routing protocols and Time Division Multiplexing. We start with some simple examples. The first show that stations which do not transmit on unrestricted channels can not be detected. To this end we use fsn(W) to denote the set of unrestricted channel names in the code W which have transmission occurrences. Formally fsn(W) is defined inductively on (a possibly open system term) W as the least set such that

alternative to cable or DSL. Basically it operates on two layers such as Physical layer (PHY) and Medium Access Control (MAC) layer. In WiMAX, security is implemented at the security sub layer of the MAC. Both the layers are susceptible to several attacks. The security sub layer of IEEE 802.16d standard defines the security mechanisms for fixed and IEEE 802.16e standard defines the security mechanisms for mobile network. The security sub layer supports to verify the user, authorize the user and provide encryption support for the key transfer and data traffic. IEEE 802.16e, the mobile WiMAX offers more enhancements over 802.16d. IEEE 802.16d standard security design is based on PKMv1 (Privacy and Key Management Version 1) protocol but it has major security problems. The authentication process in PKMv1 is one way process, in which BS authenticate MS but not vice versa. It leads to vulnerability and reason for many attacks. In PKMv2 protocol, it is modified as mutual authentication in which both MS and BS authenticate each other. IEEE 802.16e uses superior encryption methods and has more secure key management protocol. But still many security issues are yet to be solved.

In this paper, we have proposed a PHY- MAC cross-layer cooperative protocol which can support PNC for cooperative wireless networks with bidirectional tra ffi c. The proposed cross- layer protocol considers both the MAC layer and the PHY layer operation. We have shown by simulation that the proposed protocol can work flexibly in realistic channel conditions and achieve better performance than the previous protocol as well as the traditional protocol in terms of the system throughput, end-to-end latency, and the energy efficiency. With the above advantages, the proposed protocol can be employed in various ad hoc cooperative wireless networks.

where the path loss exponent n varies from 2 to 6 [16], although is most commonly used as 2 or 4. For the receiver to correctly receive the packet, the SNR must be over a certain threshold. As long as the receive SNR is maintained above this threshold, the transmit power level at the sender can be reduced, directly reducing energy consumption at the sender. The adaptation of the sender’s transmit power level is called power control and is the main tool used to conserve energy during active communication. For the remainder of this chapter, we use power level to mean transmit power level. Finally, energy is consumed to compensate for lost packets, generally via some number of retransmissions of the lost packets. While reliability is generally the domain of the transport layer, the MAC layer in most wireless devices compensates for some packet failure by retransmitting the packet up to some retransmit limit number of times before considering the packet lost. For current energy conserving protocols, this cost is only considered by protocols that aim to avoid low quality channels and so avoid needing to retransmit packets.

Wireless Local Area Networks (WLANs) are cost effective and desirable gateways to mobile computing. They allow computers to be mobile, cable less and communicate with speeds close to the speeds of wired LANs. These features came with expensive price to pay in areas of security of the network. This paper identifies and summarizes these security concerns and their solutions. Broadly, security concerns in the WLAN world are classified into physical and logical. The paper overviews both physical and logical WLANs security problems followed by a review of the main technologies used to overcome them. It addresses logical security attacks like man- in-the-middle attack and Denial of Service attacks as well as physical security attacks like rouge APs. Wired Equivalent Privacy (WEP) was the first logical solution to secure WLANs. However, WEP suffered many problems which were partially solved by IEEE802.1x protocol. Towards perfection in securing WLANs, IEEE802.11i emerged as a new MAC layer standard which permanently fixes most of the security problems found in WEP and other temporary WLANs security solutions.

It works both functionality like distributed as well as differentiated services, when MAC layer receives the higher layer data’s (frame), which contains the user priority (UP) and it maps to access categories (AC). AC contains different priority level of accessing the wireless medium. Here in EDCF access categories are defined up to eight categories [15]. To access the AC, EDCF defines access parameters like in DCF, that parameters are Cmin, Cmax, AIFS (Arbitration Inter Frame Spacing) and transmission opportunity time(TXOP), TXOP is defined as an interval of time duration which a station has right to initiate transmissions. During contention periods (CP), each AC of station contents for a TXOP and independently starts a back off counter after detecting the channel become ideal for AIFS time periods[16]. AIFS is set as given below