Classical works concerned with the throughput and delay analysis of random accessprotocols (e.g., Aloha or CSMA) rely on strong assumptions. One is that the point process comprising of both newly generated and retransmitted (due to collisions) packets is a Poisson process (Abramson , Kleinrock and Tobagi , and more recently Yang and Yum ). A related assumption is that, at each source, packets arrive as a blocked Poisson process, in the sense that at most one packet can be backlogged at any source (Tobagi  or Beuerman and Coyle ); this model is related to the infinite source model in which each source generates a single packet during its lifetime (Lam ). Another related and simplifying assumption is to discard the buffered packets at the beginning of a transmission period for a source (Takagi and Kleinrock ).
• token passing provides performance values that are, for the most part, isolated from frame sizes, level of nodal range, and external data traffic, while CSMA-CD performance is extremely dependent upon such variables. Other than this important distinction, the performance exhibited by both network media accessprotocols is very similar, in that both token ring and Ethernet meet the demands of high-quality isochronous applications, i.e., a mean throughput rate being equal to or less than the playback rate; latency and jitter values of 20 to 400 milliseconds and < 80 milliseconds, respectively; and error loss rates between 0.01--0.001. The question, then, is not so much one of capability but of the anticipated requirements for the network application, such as number of users, the type of isochronous media and required message size, and presence and intensity of other data traffic.
In this paper, the performance of a Cognitive Radio Network operating in TV bands using the slotted ALOHA and the non-persistent CSMA protocol  is studied. Slotted Aloha and CSMA are simple, mature, well-known and effective random accessprotocols. They have been suggested for use in CR networks and TV white spaces in several recent studies [6-8]. The main contribution of this paper is to adapt OFDM physical layer with multiple channel widths to specify the basis for operation of cognitive radio in the contiguous and noncontiguous TV bands. Also, the paper aims to investigate the performance of FCN and FCS type OFDM on scalable channel width in TV bands with different MAC protocols.
In , a novel slotted DSA protocol named T-MAC protocol is proposed. The super frame structure of T- MAC is shown in Figure 5. Each super frame consists of one reservation frame, K information frames and one acknowledgment frame. Each reservation frame contains one sensing slot and N reservation slots. Correspond- ingly, each information frame and acknowledgment frame consists of N information slots and acknowledg- ment slots. In order to decide which channel is available in current slot, all nodes must sense data channels in sensing slots. Each reservation slot is dedicated to the reservation of the corresponding information slot and acknowledgment slot. Each reservation period is a reser- vation process implemented through three-phase dialo- gues, named reservation request (RR), reservation confirmation (RC) and deciding to send (DTS). Setting several reservation periods in one reservation slot is to enhance the reservation success rate, which can facilitate concurrent transmissions. In the T-MAC, data packets and ACK packets can be protected simultaneously through the special acknowledgment frames. An effi- cient power control mechanism is also provided, which can significantly increase the space reuse efficiency. Moreover, the negative impact caused by the multi- channel hidden terminal problem can be efficiently reduced. In addition, the multi-channel exposed term- inal problem is also defined in this investigation and the authors explained that this problem can also be solved. Figures 6 and 7 present the network throughput and access delay of the T-MAC and DSA-MAC , respec- tively. We can observe from the simulation results that the T-MAC obviously outperforms the DSA-MAC.
Satellite access networks provide a wide range of services for civil and military applications. These services include mobile data transfer, localization, satellite television and Internet web traffic. The Second Generation DVB Interactive Satellite Services (DVB-RCS2) [? ] was recently introduced as a renewed standard for satellite communications and is specifically designed for Internet based services. Internet traffic is highly dominated by short-lived connections [? ] and message exchanges, as far as mobile applications have gained the largest part of the Internet share. As shown in [? ], the performance of access scheme are strongly linked to the traffic characteristics and in particular to the size of the file transferred. In addition, the advent of IoT (Internet of Things) services is boosting the bursty nature of the Internet traffic: such an evolution of the traffic nature requires adequate measurements on the multiple accessprotocols, in order to settle the suitability of either a Random Access (RA) or a Dedicated Access (DA). In this paper, a study on a generalized case of a Coded Slotted Aloha (CSA) is presented, showing that the random choice of information and redundancy lengths can improve the performance, in terms of throughput. In particular, runned simulations show that the design of a load control mechanism can help in obtaining a reasonable
the year 1995 with the help of idea used in Wireless Personal Area Network (WPAN). WBAN was developed to continuously monitor the aged group of population and also to monitor the patients suffering from chronic diseases. Also with the help of WBAN working parents can monitor their children from a far away place. In the proposed paper, two multiple accessprotocols suitable for IEEE 802.15.6 standard namely, Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and Time Division Multiple Access (TDMA) are analyzed using OMNeT++ simulation tool in terms of its successful transmissions, number of packets lost and percentage of packets received and lost at the coordinator node.
of attention has been focused on exploiting temporal and/or spatial reuse of acoustic channels to improve the through- put. For instance, Slotted FAMA (S-FAMA) uses time slot- ting in order to lower the probability of collisions by align- ing packet transmissions into slots (as in Slotted Aloha) while Propagation-delay-tolerant Collision Avoidance Pro- tocol (PCAP)  allows a node to send multiple reservation requests for transmission time slots (i.e., request to transmit, RTS). In Underwater-FLASHR (UW-FLASHR) , time slots are divided into reservation and data transmission pe- riods to realize efficient channel reservation and to minimize data packet losses caused by control packet exchanges. For better channel utilization, most protocols attempt to build a Time Division Multiple Access (TDMA) schedule using brute-force learning via repeated trial-and- error  or solv- ing computationally hard optimal scheduling. Key insights from TDMA-based scheduling methods allow us to enhance conventional CSMA-like random channel accessprotocols as follows. We need to ensure that transmissions are scheduled carefully such that they do not interfere with the reception of each others’ packets by their intended receivers. To sat- isfy this requirement, each node must evaluate the collision conditions for neighboring packet receptions prior to trans- mitting a packet. Recall that a collision occurs when a re- ceiver tries to decode a packet when more than one packet arrives from different senders simultaneously . The key in- tuition is that each node can predict whether its upcoming packet transmission will collide with another’s if it has the neighboring nodes’ propagation delay information and their transmission schedules. Figure 6 demonstrates the notion of temporal reuse. Node x sends a DATA packet to node z in Figure 6(a) and again at a later time another DATA packet to node y in Figure 6(b). Node z sends an acknowl- edgment (ACK) back to node x as node y is about to receive the transmission from node x in Figure 6(c). Finally, node y sends an ACK back to node x in Figure 6(d). This case enables the data and ACKs to be transmitted and received without any collision.
Studies in multiple accesses have been limited to basic networks incorporating several transmitters with one destination. As such, it definitely does not present the self- organizing wireless sensor networks known to have several dynamic pairs of transmitters and receivers. To create extension of MAC operation for multi-destination networks, researchers explored the problem of contention- based access that relate to wireless networks using two fixed receivers and employed conflict algorithms to determine bounds on maximum stable throughout (Nguyen, Katz, Noble, and Satyanarayanan, 1996). The Group time-division multiple access (TDMA) algorithm was employed as a time-division mechanism in a network with two destinations for the purpose of separating groups of nodes containing packets of data destined for different locations. Transmission scheduling idea is not new even though how it is used in this context. Depending on traffic need, each group is allocated time. Analysis of TDMA was undertaken with focus on throughput properties and best time allocation was ascertained as a function of loads offered independent of any underlying multiple accessprotocols in each group of users. The same analysis can be undertaken in multi-destination networks with arbitrary topology (Ali et al ., 2006). The assumption with a fixed pair of transmitter and receiver is that it contrasts the dynamic and independent design of sensor networks where all nodes are able to transmit and receive packets of data as source-destination pairs for the purpose of relaying the same (Maheshwari, Gupta, and Das, 2006). Assuming that only one transceiver for each node exists; simultaneous packet transmission and reception by any node within a network must be ruled out. This calls for the need to create a mechanism that activates nodes to function as transmitters or receivers (Demirkol, Ersoy, and Alagoz, 2006). The need to create such a mechanism cannot be avoided. This is because the problem of achieving best channel access schedule for multi-hop networks and network partitioning into activation sets is NP-complete and requires practical solutions (Tang and Garcia-Luna- Aceves, 1999). We introduce in this paper these issues based on limited knowledge of network connectivity map to partition nodes into disjoint transmitter-receiver sets. Instead of creating problem-free schedules like in link scheduling, we may consider a room for multiple transmissions for each receiver and rely on one MAC protocol to resolve any problems that may not be avoided.
But, as they know the required spreading sequences can’t be deterred by spread spectrum. However, with the help of different cryptographic schemes in which assignment of key takes place can be used to hide the control Channels (or messages).Use of multiple accessprotocols allows mobile users to share the wireless medium in the network which makes communication in mobile networks more efficient. However, to maintain the efficiency of the multiple access protocol allocation of access and resources to mobile users must be periodically updated.
211 In pursuit of low computational cost requirements of wireless CDMA sensor networks, there has been limited effort to investigate source and modulation schemes, particular signature waveforms, designing simple receiver models, and other signal synchronization problems. If it is shown that the high computational complexity of CDMA could be traded with its collision avoidance feature, CDMA protocols could also be considered as candidate solutions for sensor networks. Lack of comparison of TDMA, CSMA or other medium accessprotocols in a common framework is a crucial deficiency of the literature. Common wireless networking experience also suggests that link-level performance alone may provide misleading conclusions about the system performance. Similar conclusion can be drawn for upper layers as well. Hence, the more layers contributing to the decision, the more efficient the system can be. For instance, the routing path could be chosen depending on the collision information from the medium access layer. Moreover, layering of the network protocols creates overheads for each layer which causes more energy consumption for each packet. Therefore, integration of the layers is also a promising research area which has to be studied more extensively.
The experimentation described in the previous section has taken place in many different venues. When at home in Ireland we have the advantage of making use of various different frequency bands for experimentation, thanks to a Test & Trial scheme, driven by the national regulator authority. The Irish spectrum regulator, Comreg, enables cognitive radio and dynamic spectrum access activities to take place under a wireless test and trial licensing scheme. The regulators promise that licence applications will be turned around as soon as possible, typically within 10 days after receipt of a completed application. And more importantly they state that all available radio frequency bands will be considered for a test or trial licence, including the UHF band; radio spectrum’s ‘sweetspot’. We have availed ourselves of this favourable spectrum licensing regime in Ireland to conduct tests and trials of Iris- based cognitive radio and dynamic spectrum access systems outside of the lab and across Ireland.
to VANET scenarios. First, we show that the average positions of a given number of points of a PPP falling in a segment with finite length are equally spaced. Then, assuming a silencing mechanism at each hop, we derive a recursive (hop-wise) theoretical performance evalua- tion framework which exploits the assumption of fixed and equally spaced vehicles positions in each retrans- mission hop. In particular, this performance analysis is likely to be representative of the average (with respect to the nodes’ spatial distribution) performance of the broadcast protocols at hand, as will be confirmed by ns- 2 simulations. Moreover, the proposed analytical model applies also to other vehicle spatial distributions, pro- vided that the average inter-vehicle distance is fixed. The impact of node mobility will also be evaluated. Although we consider two novel illustrative broadcast protocols, we underline that our approach is general.
First, it is important for every network administrator to help reduce the number of DoS attack launch platforms. Do not let your network be the origin point for a DoS attack; keep hosts secure and eliminate compromised hosts from the network immediately. There are several mechanisms available on routers to thwart certain kinds of DoS attacks. Many of these attacks require use of invalid or spoofed source addresses. For example, invalid addresses are used in SYN flood attacks to ensure that the TCP handshake on the target host times out waiting for a response (see Section 6.3.2). There are several ways to filter out these improperly-addressed packets. Access control lists are a general filtering facility available on all routers (see Section 4.3). Black hole routing can also be useful, and works on all routers (see Section 4.4.6). Most Cisco routers support a facility called Unicast Reverse-Path Forwarding Verification that uses the route table to detect and drop improperly- addressed packets (see Section 4.4.7). Where possible, you should log occurences of bad packets, logging these violations can help identify compromised hosts that need to be removed from your network. Of course, detection will depend on reviewing the router logs on a regular basis.
The main advantages of the restricted access approach are for the lead institution and nominated principal in- vestigator who protect their intellectual property asso- ciated with the trial. The main disadvantage is that there can be only one named institution and investigator, even if the trial was developed by a multidisciplinary and multi-institution research team. This approach implies that the protocol is owned by the lead institution, thus reducing the collegiality between the lead investigators and also between the lead investigators and site colla- borators. Other disadvantages lie in defining who ‘needs to know’ about the study protocol during the site evalu- ation of the study, and how much information would constitute a breach of confidence: it is unclear whether, for example, presentation of the protocol at departmen- tal rounds could constitute a breach of NDA. These defi- nitions should be clear, because NDAs declare the threat of legal action if the protocol is shared unnecessarily, al- though it is not evident what legal remedies might be applied. As well, the use of NDAs involves costs to the lead site and both potential and actual collaborators, be- cause the agreement must be reviewed and signed by each site’s lead investigator, lawyers and institutional representatives before the site investigator can even evaluate the merits of the protocol and the feasibility of study participation at that centre. This extra step, before the protocol can be discussed locally, will slow the process of site recruitment, and may even discourage sites from joining a trial, particularly when the subsequent process of study approvals is well known to be onerous .
S-MAC, US-MAC protocols are used to solve the idle listening problem. Based on the thesis, low energy efficiency is needed to transmit the packets from source to destination at the time of solving the ldle listening problem. In future energy models can be used to find out the energy efficiency of MAC protocols. One of the key applications of the sensor networks which is widely adapted due to its huge number of implementations and usages, in the MAC protocols. Although, this application is known for its high demands of energy in order to perform its tasks in the best manner as many as possible. Since the main drawback that faces most in the transmission of packets in sensor networks is the fact that the sensor network suffers from a very limited power supply. Therefore, the need to optimize the energy consumption in idle listening problem is a fact must be faced. Since most the energy savings research was focusing on minimizing the energy consumed by the radio component (RF radio) in the sensor nodes by reducing the number of messages transmitted and received, considering the energy consumed and the sensing components in the sensor
Unlike Cross-layer adaptation, where protocols, operating at different layers from the protocol stack, exchange information’s (directly or not), to adapt their functioning to a certain network constraint, multi-layer adaptation is a combination of a number of self-adaptation processes, triggered at different layers, but independently. As cited above, cross-layer adaptation has a several advantages, but the strong dependence between participant protocols limits choices about the communication protocols already used in a specific scheme. So in order to keep the validity of our approach although the modification of one contributor protocol, we choose to implement the quality of service at different layers. Each protocol will use its proper resources to respond the type of service required by an application. To achieve this objective, we opted for three quality of services mechanisms: QOS routing with an OLSR extension with QOS support, EDCAF (Enhanced Distributed Coordinate Function), and FEC (forward error correction). Our goal, through the combination of all those mechanisms is to offer a higher level of QOS, especially by enhancing the average end–to-end delay for delay sensitive traffics. QOLSR is a proactive routing protocol, and the type of traffic is not always known when routes calculation is performed. This fact leads us to say, that paths with QOS will convey both traffics with and without constraints, hence the idea of adding a priorities management at MAC level that will give a certain privilege to delay-sensitive applications. This distinction will fill the absence of a service differentiation at routing level on the one hand, and improve the local delay latency for real- time traffic on the other hand. EDCA aims then to add the differentiation of traffics in order to privilege those with high priority for the channel access, the same for the use of the FEC .They are both meant to enhance the end-to-end delay by avoiding the increase of the number of retransmissions. We prove that cooperating those three QOS mechanisms, even in a complete independent and primitive way enhances the network performance. Our study, aims to demonstrate the reliability of these assumption in the first place, and to locate its validation perimeter in a second place, especially for the real time traffics.
Multi-client security: As this scheme is a generalization of the square-root one, our modifications extend naturally to provide multi-client security. Again, each client should have their own ORAM which they read from. Writing to other clients’ ORAMs is done by inserting the block into the top level of their cache and then shuffling as necessary. The only difference this time is that each level of the cache must be independently au- thenticated. Since the cache levels are now hash tables, and computing a MAC over every level for each access would require downloading the whole data structure, we can instead use a Merkle tree . This allows for efficient verification and updating of pieces of the cache without having access to the entire thing, and it maintains poly- logarithmic communication complexity. The root of the Merkle tree will contain the counter that is incremented by the ORAM owner when they perform an access. Deamortizing: Other authors have proposed deamortized versions of the hierarchical construction that achieve worst-case poly-logarithmic complexity, such as Kushilevitz et al.  and Ostrovsky and Shoup . We will use as an example the “warm-up” construction from Kushilevitz et al. , Section 6.1. This is a direct deamortization of the original hierarchical scheme described above. They deamortize by using three sepa- rate hash tables at each level of the ORAM, labelled “active”, “inactive”, and “output”. Instead of shuffling all at one time after 2 j−1 accesses (which would lead to worst case O(N) complexity), their approach is now different. When the cache fills up at level j, it is marked “inactive”, and the old “inactive” buffer is cleared and marked “active”. The idea will be that the “inactive” buffer is shuffled over time with each ORAM ac- cess, so that no worst-case O(N) operations are required. As it is shuffled, the contents are copied into the “output” buffer. Accesses can continue while the “inactive” buffer is being shuffled, as long as a read operation searches both the “active” and “inactive” buffers (since a block could be in either one).
Motivated by the fact that the Transmission Control Protocol (TCP)/Internet Protocol (IP) suite is the de-facto standard for computer communications in today’s networked world, IP based solutions could be the future for networks that form the IoT . In order to tackle the technical challenges, such as extensive protocol overheads against memory and computational limitations of sensor devices, the Internet Engineering Task Force (IETF) has taken the lead to develop and standardize communication protocols for resource constrained devices, including Routing Protocol for Low Power and Lossy Networks (RPL) , and Constrained Application Protocol (CoAP) . Besides, the IP Smart Object Alliance (IPSO)  also actively promotes the use of IP version 6 (IPv6) embedded devices for machine-to-machine (M2M) applications. Although it is still in its early stage to be commercialized, there are already a substantial number of IP-based WSN solutions supported by growing availability of products and systems.