The document summarizes a proposed novel backoff algorithm called Pause Count Backoff (PCB) for channel access in IEEE 802.11 wireless networks. PCB observes the number of pauses in a node's backoff procedure to estimate the number of active stations and set an appropriate contention window size. Simulation results show PCB outperforms other algorithms like DCF, EIED, and AEDCF in terms of goodput, fairness index, and end-to-end delay under different network conditions.
This document evaluates the performance of different backoff algorithms for the IEEE 802.15.4 standard using double sensing. It simulates the binary exponential backoff algorithm defined in the standard as well as three other algorithms: exponential increase exponential decrease, exponential increase linear decrease, and exponential increase multiplicative decrease. The results show that for higher node loads, the three alternative algorithms generally perform better than the standard binary exponential backoff in terms of throughput, delay, and energy consumption. Of the four algorithms evaluated, exponential increase exponential decrease consistently provided the best performance.
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
1) The document analyzes the quality of service capabilities of the IEEE 802.11e standard through simulation.
2) It simulates four access categories (voice, video, data, background) on the EDCA mechanism and finds that voice and video have higher throughput and lower delay, showing that 802.11e provides service differentiation.
3) A comparison of 802.11e EDCA and legacy DCF shows that while DCF has slightly higher overall throughput, EDCA experiences less variable data dropping due to its prioritized access scheme.
This document provides an overview of queuing theory models used to analyze the performance of IEEE 802.11 wireless networks. It discusses how queuing models can measure metrics like throughput, delay, and packet loss. It also reviews the IEEE 802.11 standard, including the distributed coordination function (DCF) used for medium access control and quality of service enhancements in 802.11e. The goal is to identify the most accurate queuing or probability models for designing wireless LANs that consider performance and meet QoS requirements.
This document summarizes a study on the performance of real-time and non-real-time traffic in IEEE 802.11 wireless local area networks (WLANs) using the network simulator NS2. The study evaluates the impact of the distributed coordination function (DCF) on throughput, packet loss, and delay. It describes simulations with various traffic types, including voice, video, and data, under different load conditions. The results show the packet loss, throughput, and delay for each simulation case.
General Model for Single and Multiple Channels WLANs with Quality of Service ...ijwmn
In this paper we develop an intergraded model for request mechanism and data transmission in the uplink phase in the presence of channel noise. This model supports quality of service. The wireless channel is prone to many impairments. Thus, certain techniques have to be developed to deliver data to the receiver. We calculated the performance parameters for single and multichannel wireless networks, like the requests throughput, data throughput and the requests acceptance probability and data acceptance probability. The proposed model is general model since it can be applied to different wireless networks such as IEEE802.11a, IEEE802.16e, CDMA operated networks and Hiperlan\2.
Quality of Service for Video Streaming using EDCA in MANETijsrd.com
Mobile Ad-hoc network(MANET) is a collection of wireless terminals that are able to dynamically form a temporary network. To establish such a network no fixed infrastructure is required. Here, it is the responsibility of network nodes to forward each other's packets and thus these nodes also act as routers. In such a network resources are limited and also topology changes dynamically. So providing Quality of service(QoS) is also necessary. QoS is more important for real time applications for example Video Streaming. IEEE 802.11e network standard supports QoS through EDCA technique. This technique does not fulfill the requirements of QoS. So, in this project modified EDCA technique is proposed to enhance QoS for Video Streaming application. This technique is implemented in NS2 and compared with traditional EDCA.
QOS-APCVS: AN ENHANCED EPS-IMS PCC ARCHITECTURE PROPOSAL TO IMPROVE MOBILE SE...ecij
IP Multimedia Subsystem’s (IMS) presents the framework architecture which can provide multimedia services for Evolved Packet System (EPS). In busy network, the main failures are service blocking, handover outage and non satisfying QoS criteria. So we aim to improve dependability of dedicated bearer
establishment in EPS-IMS Network. In mobile access network, we consider service is available if it is admitted by base station and is reliable if it is still supported in handover position. In core network, we consider service as reliable if its QoS criteria are satisfied. So we propose a new Qos Provisioning solution. To provide new application or to support handover service in busy network, our approach preempts resources by utility factor instead of priority consideration in existing works. In addition to
bandwidth reservation our solution allows core network reservation to improve the delay of real time service and minimize the loss rate of non-real time services.
Adjustment Delay Scheme to Improve Performance IEEE 802.15.4 NetworksTELKOMNIKA JOURNAL
The challenges of CSMA/CA as following: first, when the device nodes detect the channel in busy
condition, the device nodes have to increase the value of backoff exponent which cause range of blind
backoff process also increase. Second, the blind backoff process will cause lower channel utilization and
more energy consumptions. This article proposes a scheme to improve IEEE 802.15.4 medium access
control, called adjustment delay scheme (ADES). This article also presents a comprehensive Markov chain
analysis to predict the probability of successful transmission, network goodput, bandwidth utilization and
total network energy consumption. The validity of the model analysis is proven by precisely matching the
simulation experiments. ADES performs better than those of other algorithms in term of the probability of
successful packet transmission, network goodput, bandwidth utilization as well as energy consumption in
the networks.
This document evaluates the performance of different backoff algorithms for the IEEE 802.15.4 standard using double sensing. It simulates the binary exponential backoff algorithm defined in the standard as well as three other algorithms: exponential increase exponential decrease, exponential increase linear decrease, and exponential increase multiplicative decrease. The results show that for higher node loads, the three alternative algorithms generally perform better than the standard binary exponential backoff in terms of throughput, delay, and energy consumption. Of the four algorithms evaluated, exponential increase exponential decrease consistently provided the best performance.
Welcome to International Journal of Engineering Research and Development (IJERD)IJERD Editor
1) The document analyzes the quality of service capabilities of the IEEE 802.11e standard through simulation.
2) It simulates four access categories (voice, video, data, background) on the EDCA mechanism and finds that voice and video have higher throughput and lower delay, showing that 802.11e provides service differentiation.
3) A comparison of 802.11e EDCA and legacy DCF shows that while DCF has slightly higher overall throughput, EDCA experiences less variable data dropping due to its prioritized access scheme.
This document provides an overview of queuing theory models used to analyze the performance of IEEE 802.11 wireless networks. It discusses how queuing models can measure metrics like throughput, delay, and packet loss. It also reviews the IEEE 802.11 standard, including the distributed coordination function (DCF) used for medium access control and quality of service enhancements in 802.11e. The goal is to identify the most accurate queuing or probability models for designing wireless LANs that consider performance and meet QoS requirements.
This document summarizes a study on the performance of real-time and non-real-time traffic in IEEE 802.11 wireless local area networks (WLANs) using the network simulator NS2. The study evaluates the impact of the distributed coordination function (DCF) on throughput, packet loss, and delay. It describes simulations with various traffic types, including voice, video, and data, under different load conditions. The results show the packet loss, throughput, and delay for each simulation case.
General Model for Single and Multiple Channels WLANs with Quality of Service ...ijwmn
In this paper we develop an intergraded model for request mechanism and data transmission in the uplink phase in the presence of channel noise. This model supports quality of service. The wireless channel is prone to many impairments. Thus, certain techniques have to be developed to deliver data to the receiver. We calculated the performance parameters for single and multichannel wireless networks, like the requests throughput, data throughput and the requests acceptance probability and data acceptance probability. The proposed model is general model since it can be applied to different wireless networks such as IEEE802.11a, IEEE802.16e, CDMA operated networks and Hiperlan\2.
Quality of Service for Video Streaming using EDCA in MANETijsrd.com
Mobile Ad-hoc network(MANET) is a collection of wireless terminals that are able to dynamically form a temporary network. To establish such a network no fixed infrastructure is required. Here, it is the responsibility of network nodes to forward each other's packets and thus these nodes also act as routers. In such a network resources are limited and also topology changes dynamically. So providing Quality of service(QoS) is also necessary. QoS is more important for real time applications for example Video Streaming. IEEE 802.11e network standard supports QoS through EDCA technique. This technique does not fulfill the requirements of QoS. So, in this project modified EDCA technique is proposed to enhance QoS for Video Streaming application. This technique is implemented in NS2 and compared with traditional EDCA.
QOS-APCVS: AN ENHANCED EPS-IMS PCC ARCHITECTURE PROPOSAL TO IMPROVE MOBILE SE...ecij
IP Multimedia Subsystem’s (IMS) presents the framework architecture which can provide multimedia services for Evolved Packet System (EPS). In busy network, the main failures are service blocking, handover outage and non satisfying QoS criteria. So we aim to improve dependability of dedicated bearer
establishment in EPS-IMS Network. In mobile access network, we consider service is available if it is admitted by base station and is reliable if it is still supported in handover position. In core network, we consider service as reliable if its QoS criteria are satisfied. So we propose a new Qos Provisioning solution. To provide new application or to support handover service in busy network, our approach preempts resources by utility factor instead of priority consideration in existing works. In addition to
bandwidth reservation our solution allows core network reservation to improve the delay of real time service and minimize the loss rate of non-real time services.
Adjustment Delay Scheme to Improve Performance IEEE 802.15.4 NetworksTELKOMNIKA JOURNAL
The challenges of CSMA/CA as following: first, when the device nodes detect the channel in busy
condition, the device nodes have to increase the value of backoff exponent which cause range of blind
backoff process also increase. Second, the blind backoff process will cause lower channel utilization and
more energy consumptions. This article proposes a scheme to improve IEEE 802.15.4 medium access
control, called adjustment delay scheme (ADES). This article also presents a comprehensive Markov chain
analysis to predict the probability of successful transmission, network goodput, bandwidth utilization and
total network energy consumption. The validity of the model analysis is proven by precisely matching the
simulation experiments. ADES performs better than those of other algorithms in term of the probability of
successful packet transmission, network goodput, bandwidth utilization as well as energy consumption in
the networks.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
An adaptive power controlled mac protocol forambitlick
The document summarizes an adaptive power controlled MAC protocol called ATPMAC that is proposed to improve network throughput in wireless ad hoc networks using a single channel and transceiver. ATPMAC allows concurrent transmissions without interference by controlling transmission power. It improves on prior work by requiring only one RTS/CTS exchange for multiple concurrent transmissions, avoiding additional signaling overhead, and providing synchronization solutions so concurrent data transmissions can occur despite propagation delays. Simulations showed ATPMAC improved network throughput by up to 136% compared to IEEE 802.11.
1) The document discusses the usage of Erlang formulas in simulating and analyzing video flow transfer in IP networks.
2) The Erlang B formula was used to calculate data loss probability under different network loads and bandwidths. The Erlang C formula was used to calculate the probability of insertion into waiting queues.
3) The formulas were simulated in MATLAB and also tested in a real network environment using designed video sources. The results from the simulations were compared to the real measurements.
This paper presents the design and performance comparison of a two stage
operational amplifier topology using CMOS and BiCMOS technology. This conventional op
amp circuit was designed by using RF model of BSIM3V3 in 0.6 μm CMOS technology and
0.35 μm BiCMOS technology. Both the op amp circuits were designed and simulated,
analyzed and performance parameters are compared. The performance parameters such as
gain, phase margin, CMRR, PSRR, power consumption etc achieved are compared. Finally,
we conclude the suitability of CMOS technology over BiCMOS technology for low power
RF design.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
EFFECTS OF MAC PARAMETERS ON THE PERFORMANCE OF IEEE 802.11 DCF IN NS-3ijwmn
This paper presents the design procedure of the NS-3 script for WLAN that is organized according to the
hierarchical manner of TCP/IP model. We configure all layers by using NS-3 model objects and set and
modify the values used by objects to investigate the effects of MAC parameters (access mechanism, CWmin,
CWmax and retry limit) on the performance metrics viz. packet delivery ratio, packet lost ratio, aggregated
throughput, and average delay. The simulation results show that RTS/CTS access mechanism outperforms
basic access mechanism in saturated state, whereas the MAC parameters have no significant impact on
network performance in non-saturated state. A higher value of CWmin improves the aggregated throughput
in expense of average delay. The tradeoff relationships among the performance metrics are also observed
in results for the optimal values of MAC parameters. Our design procedure represents a good guideline for
new NS-3 users to design and modify script and results greatly benefit the network design and
management.
The document evaluates data drop performance in wireless LANs using Time-to-Live (TTL) and packet fragmentation. It simulates wireless network traffic with and without TTL/fragmentation using OPNET. The results show that using TTL and fragmenting large packets into smaller chunks significantly reduces data dropped compared to not using these techniques. Specifically, data drop is reduced when packets are fragmented into 1024 byte chunks and a TTL is applied, leading to higher throughput and less buffer overflow.
Design and Implementation of QoS Aware Priority based MAC for Delay Sensitive...Eswar Publications
Networking is a trending research area where the various research took place. Diversified filed of the Network is Sensor Network, which is a centrally adopted due to features and flexibility of sensors. Various disciplines like a military, medical, forest, Industries, Health monitoring and more, where WSN is established. Sensors have various pitfalls like limited lifetime and Storage, installed in misanthropic environments. Frequently power up or replace an energy source is a crucial task. Data communication in WSN is possible in the MAC layer. MAC is responsible for node schedule and sensing task. Collision and retransmission also lead to waste of energy. Variety of MAC protocols are developed for various qualities of service factors like energy, latency, reliability, delay, jitter, etc., however, none of them are given a satisfactory result for various QoS parameters. To overcome some of the pitfalls we need to achieve various QoS parameters. In this Research MAC is designed with a priority mechanism over clusters. Data with the highest priority are sent without or with a very negligible amount of delay. Higher priority packets are transmitted before a no prioritized packet. Using various priorities, the node energy, low delay and high throughput are achieved over standard MAC Protocols.
This document provides an overview of high speed networks including Frame Relay networks, Asynchronous Transfer Mode (ATM), ATM protocol architecture, logical connections, cells, service categories, and high speed LANs. It discusses the architecture, user data transfer, and call control of Frame Relay networks. For ATM, it describes the protocol model, logical connections, cells, adaptation layer, and service categories. It also provides an introduction to emerging high speed LAN technologies.
The document discusses buffer sizing algorithms for 802.11 wireless networks. It proposes two novel dynamic buffer sizing algorithms - eBDP and ALT that achieve high throughput while maintaining low delay across different network conditions. Experimental results on a production WLAN and testbed demonstrate that the algorithms significantly improve performance compared to using fixed buffer sizes. The algorithms adapt the buffer size based on network parameters like load and traffic patterns.
An Accurate Performance Analysis of Hybrid Efficient and Reliable MAC Protoco...IJECEIAES
The document analyzes the performance of the Hybrid Efficient and Reliable MAC (HER-MAC) protocol in Vehicular Ad Hoc Networks (VANETs) under non-saturated conditions. It develops 1-D and 2-D Markov chain models to evaluate the packet delivery ratio of safety and non-safety applications respectively. The models consider elements like backoff freezing timer, backoff stages, and short retry limit to better accommodate IEEE 802.11p specifications and provide more accurate estimations of channel access and packet delivery ratio. Simulation results validate the analytical models and show their performance outperforms existing models, especially in terms of packet delivery ratio under different numbers of vehicles and contention windows.
AN OPTIMUM ENERGY CONSUMPTION HYBRID ALGORITHM FOR XLN STRATEGIC DESIGN IN WSN’SIJCNCJournal
In this paper, X-Layer protocol is originated which executes mobility error prediction (MEP) algorithm to calculate the remaining energy level of each node. This X-Layer protocol structure employs the mobility aware protocol that senses the mobility concerned to each node with the utilization of Ad-hoc On-Demand Distance Vector (AODV), which shares the information or data specific to the distance among individual nodes. With the help of this theory, the neighbour list will be updated only to those nodes which are mobile resulting in less energy consumption when compared to all (static/mobile) other nodes in the network. Apart from the MEP algorithm, clustering head (CH) election algorithm has also been specified to identify the relevant clusters whether they exists within the network region or not. Also clustering multi-hop routing (CMHR) algorithm was implemented in which the node can identify the cluster to which it belongs depending upon the distance from each cluster surrounding the node. Finally comprising the AODV routing protocol with the Two-Ray Ground method, we implement X-Layer protocol structure by considering MAC protocol in accordance to IEEE 802.15.4 to obtain the best results in energy consumption and also by reducing the energy wastage with respect to each node. The effective results had been illustrated through Network Simulator-II platform.
This document compares MPLS protection switching and OSPF rerouting through simulations. It describes MPLS recovery mechanisms like link protection and the Haskin scheme. It also describes OSPF mechanisms like hello protocols, link state advertisements, shortest path first calculations, and main time constants. The document discusses proposed extensions to OSPF like reducing timers and using multipath routing with local failure reactions. It describes the simulation framework used to model these protocols in NS-2 and compare their recovery performance on a sample network. The focus is on restoration speed after a failure.
Investigation and Evaluation of IEEE 802.11n Wlans Link Features Performance ...pijans
For an efficient design of wireless local-area networks (WLANs), the simulation tools are important to accurately estimate the IEEE 802.11n/ac link features for WLANs. However, this true simulation of network behavior is critical in designing high-performance WLANs. Through testing, analysis, and modeling of the proposed scheme repetitively, the design of the WLAN can be enhanced with a small budget before making its practical implementation. Many network simulation tools have been established to give solutions for this request and ns-3 is the most widely used tools among them by the research industry as an open-source network simulator. In this paper, we examine the various link features of the 802.11n WLANs under several conditions. We investigate the effects of 802.11n WLAN modulation and coding schemes (MCSs), 20MHz single channel or 40 MHz bonded channel, guard intervals (GI), frame aggregation, data encoding, number of antennas and their data rate, and link distance features of 802.11n WLAN in ns-3 when only a unique host connects with the access point (AP) and generates data traffic. Besides, the performance for an enterprise scenario proposed by the IEEE 802.11ax study group is evaluated when several hosts are simultaneously creating traffic with their associated APs. The results demonstrate that ns-3 support most of the link features of the 802.11n protocol with significant accuracy.
The document provides an overview of concepts related to the data link layer. It discusses functions of the data link layer including framing, flow control, and error detection. It also covers topics such as HDLC, PPP, channel allocation problems, multiple access protocols including ALOHA, CSMA, CSMA/CD, and channelization techniques like FDMA, TDMA, and CDMA. Specific standards for wired LANs like Ethernet and wireless LANs like IEEE 802.11 are also mentioned. Finally, it briefly discusses technologies like token bus, token ring, and virtual LANs.
In this paper, we examine WiMAX – based network and evaluate the performance for quality of service (QoS) using an idea of IEEE 802.16 technology. In our models, the study used a multiprocessor architecture organized by the interconnection network. OPNET Modeler is used to simulate the architecture and to calculate the performance criteria (i.e. throughput, delay and data dropped) that
slightly concerned in network estimation. It is concluded that our models shorten the time quite a bit for
obtaining the performance measures of an end-to-end delay as well as throughput can be used as an
effective tool for this purpose.
A SURVEY ON DIFFERENT TYPES OF CLUSTERING BASED ROUTING PROTOCOLS IN WIRELESS...Journal For Research
In most of today’s application the wireless sensor network (WSN) play an important role.WSN is an autonomous system to monitor physical and environmental conditions. It can sense and compute the information or data or message that transmitted through it. Important design issue of the Wireless sensor networks energy consumption and lifetime of the network. The design of different routing protocol is another important design issue in WSN. There are mainly broad types of routing protocols in wireless sensor networks. This paper mainly deals with different types of cluster based routing protocols in WSN. Clustering algorithms are mainly defined to reduce the energy consumption and improves the life time of the network.
Energy efficient cluster-based service discovery in wireless sensor networksambitlick
1) The document proposes an energy-efficient service discovery protocol for wireless sensor networks that exploits a cluster-based network overlay.
2) Clusterhead nodes form a distributed service registry to minimize communication costs during service discovery and maintenance.
3) The performance of the proposed integrated clustering and service discovery solution is evaluated through simulations under different network conditions.
The document proposes an energy-efficient service discovery protocol for wireless sensor networks. It uses a lightweight clustering algorithm to build a distributed directory of service registrations. Each cluster head maintains information about services in its cluster. The protocol aims to minimize communication costs during service discovery and maintenance of the distributed directory. It constructs disjoint tree clusters where high-capability nodes become cluster heads and advertise their roles, while other nodes select parents based on capability grades.
Onder het mom van COREPER worden door de Europese Unie diverse snoepreisjes georganiseerd. OPvallend is dat de leden van COREPER hun partner kunnen meenemen op een dergelijke snoepreis.
Hoe rijk is eurocommissaris Marianne Thyssen?Thierry Debels
Nieuwbakken eurocommissaris Marianne Thyssen moet een verklaring afleggen over haar vermogen. Uit dat document blijkt dat ze een aanzienlijk roerend en onroerend vermogen heeft.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
An adaptive power controlled mac protocol forambitlick
The document summarizes an adaptive power controlled MAC protocol called ATPMAC that is proposed to improve network throughput in wireless ad hoc networks using a single channel and transceiver. ATPMAC allows concurrent transmissions without interference by controlling transmission power. It improves on prior work by requiring only one RTS/CTS exchange for multiple concurrent transmissions, avoiding additional signaling overhead, and providing synchronization solutions so concurrent data transmissions can occur despite propagation delays. Simulations showed ATPMAC improved network throughput by up to 136% compared to IEEE 802.11.
1) The document discusses the usage of Erlang formulas in simulating and analyzing video flow transfer in IP networks.
2) The Erlang B formula was used to calculate data loss probability under different network loads and bandwidths. The Erlang C formula was used to calculate the probability of insertion into waiting queues.
3) The formulas were simulated in MATLAB and also tested in a real network environment using designed video sources. The results from the simulations were compared to the real measurements.
This paper presents the design and performance comparison of a two stage
operational amplifier topology using CMOS and BiCMOS technology. This conventional op
amp circuit was designed by using RF model of BSIM3V3 in 0.6 μm CMOS technology and
0.35 μm BiCMOS technology. Both the op amp circuits were designed and simulated,
analyzed and performance parameters are compared. The performance parameters such as
gain, phase margin, CMRR, PSRR, power consumption etc achieved are compared. Finally,
we conclude the suitability of CMOS technology over BiCMOS technology for low power
RF design.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
EFFECTS OF MAC PARAMETERS ON THE PERFORMANCE OF IEEE 802.11 DCF IN NS-3ijwmn
This paper presents the design procedure of the NS-3 script for WLAN that is organized according to the
hierarchical manner of TCP/IP model. We configure all layers by using NS-3 model objects and set and
modify the values used by objects to investigate the effects of MAC parameters (access mechanism, CWmin,
CWmax and retry limit) on the performance metrics viz. packet delivery ratio, packet lost ratio, aggregated
throughput, and average delay. The simulation results show that RTS/CTS access mechanism outperforms
basic access mechanism in saturated state, whereas the MAC parameters have no significant impact on
network performance in non-saturated state. A higher value of CWmin improves the aggregated throughput
in expense of average delay. The tradeoff relationships among the performance metrics are also observed
in results for the optimal values of MAC parameters. Our design procedure represents a good guideline for
new NS-3 users to design and modify script and results greatly benefit the network design and
management.
The document evaluates data drop performance in wireless LANs using Time-to-Live (TTL) and packet fragmentation. It simulates wireless network traffic with and without TTL/fragmentation using OPNET. The results show that using TTL and fragmenting large packets into smaller chunks significantly reduces data dropped compared to not using these techniques. Specifically, data drop is reduced when packets are fragmented into 1024 byte chunks and a TTL is applied, leading to higher throughput and less buffer overflow.
Design and Implementation of QoS Aware Priority based MAC for Delay Sensitive...Eswar Publications
Networking is a trending research area where the various research took place. Diversified filed of the Network is Sensor Network, which is a centrally adopted due to features and flexibility of sensors. Various disciplines like a military, medical, forest, Industries, Health monitoring and more, where WSN is established. Sensors have various pitfalls like limited lifetime and Storage, installed in misanthropic environments. Frequently power up or replace an energy source is a crucial task. Data communication in WSN is possible in the MAC layer. MAC is responsible for node schedule and sensing task. Collision and retransmission also lead to waste of energy. Variety of MAC protocols are developed for various qualities of service factors like energy, latency, reliability, delay, jitter, etc., however, none of them are given a satisfactory result for various QoS parameters. To overcome some of the pitfalls we need to achieve various QoS parameters. In this Research MAC is designed with a priority mechanism over clusters. Data with the highest priority are sent without or with a very negligible amount of delay. Higher priority packets are transmitted before a no prioritized packet. Using various priorities, the node energy, low delay and high throughput are achieved over standard MAC Protocols.
This document provides an overview of high speed networks including Frame Relay networks, Asynchronous Transfer Mode (ATM), ATM protocol architecture, logical connections, cells, service categories, and high speed LANs. It discusses the architecture, user data transfer, and call control of Frame Relay networks. For ATM, it describes the protocol model, logical connections, cells, adaptation layer, and service categories. It also provides an introduction to emerging high speed LAN technologies.
The document discusses buffer sizing algorithms for 802.11 wireless networks. It proposes two novel dynamic buffer sizing algorithms - eBDP and ALT that achieve high throughput while maintaining low delay across different network conditions. Experimental results on a production WLAN and testbed demonstrate that the algorithms significantly improve performance compared to using fixed buffer sizes. The algorithms adapt the buffer size based on network parameters like load and traffic patterns.
An Accurate Performance Analysis of Hybrid Efficient and Reliable MAC Protoco...IJECEIAES
The document analyzes the performance of the Hybrid Efficient and Reliable MAC (HER-MAC) protocol in Vehicular Ad Hoc Networks (VANETs) under non-saturated conditions. It develops 1-D and 2-D Markov chain models to evaluate the packet delivery ratio of safety and non-safety applications respectively. The models consider elements like backoff freezing timer, backoff stages, and short retry limit to better accommodate IEEE 802.11p specifications and provide more accurate estimations of channel access and packet delivery ratio. Simulation results validate the analytical models and show their performance outperforms existing models, especially in terms of packet delivery ratio under different numbers of vehicles and contention windows.
AN OPTIMUM ENERGY CONSUMPTION HYBRID ALGORITHM FOR XLN STRATEGIC DESIGN IN WSN’SIJCNCJournal
In this paper, X-Layer protocol is originated which executes mobility error prediction (MEP) algorithm to calculate the remaining energy level of each node. This X-Layer protocol structure employs the mobility aware protocol that senses the mobility concerned to each node with the utilization of Ad-hoc On-Demand Distance Vector (AODV), which shares the information or data specific to the distance among individual nodes. With the help of this theory, the neighbour list will be updated only to those nodes which are mobile resulting in less energy consumption when compared to all (static/mobile) other nodes in the network. Apart from the MEP algorithm, clustering head (CH) election algorithm has also been specified to identify the relevant clusters whether they exists within the network region or not. Also clustering multi-hop routing (CMHR) algorithm was implemented in which the node can identify the cluster to which it belongs depending upon the distance from each cluster surrounding the node. Finally comprising the AODV routing protocol with the Two-Ray Ground method, we implement X-Layer protocol structure by considering MAC protocol in accordance to IEEE 802.15.4 to obtain the best results in energy consumption and also by reducing the energy wastage with respect to each node. The effective results had been illustrated through Network Simulator-II platform.
This document compares MPLS protection switching and OSPF rerouting through simulations. It describes MPLS recovery mechanisms like link protection and the Haskin scheme. It also describes OSPF mechanisms like hello protocols, link state advertisements, shortest path first calculations, and main time constants. The document discusses proposed extensions to OSPF like reducing timers and using multipath routing with local failure reactions. It describes the simulation framework used to model these protocols in NS-2 and compare their recovery performance on a sample network. The focus is on restoration speed after a failure.
Investigation and Evaluation of IEEE 802.11n Wlans Link Features Performance ...pijans
For an efficient design of wireless local-area networks (WLANs), the simulation tools are important to accurately estimate the IEEE 802.11n/ac link features for WLANs. However, this true simulation of network behavior is critical in designing high-performance WLANs. Through testing, analysis, and modeling of the proposed scheme repetitively, the design of the WLAN can be enhanced with a small budget before making its practical implementation. Many network simulation tools have been established to give solutions for this request and ns-3 is the most widely used tools among them by the research industry as an open-source network simulator. In this paper, we examine the various link features of the 802.11n WLANs under several conditions. We investigate the effects of 802.11n WLAN modulation and coding schemes (MCSs), 20MHz single channel or 40 MHz bonded channel, guard intervals (GI), frame aggregation, data encoding, number of antennas and their data rate, and link distance features of 802.11n WLAN in ns-3 when only a unique host connects with the access point (AP) and generates data traffic. Besides, the performance for an enterprise scenario proposed by the IEEE 802.11ax study group is evaluated when several hosts are simultaneously creating traffic with their associated APs. The results demonstrate that ns-3 support most of the link features of the 802.11n protocol with significant accuracy.
The document provides an overview of concepts related to the data link layer. It discusses functions of the data link layer including framing, flow control, and error detection. It also covers topics such as HDLC, PPP, channel allocation problems, multiple access protocols including ALOHA, CSMA, CSMA/CD, and channelization techniques like FDMA, TDMA, and CDMA. Specific standards for wired LANs like Ethernet and wireless LANs like IEEE 802.11 are also mentioned. Finally, it briefly discusses technologies like token bus, token ring, and virtual LANs.
In this paper, we examine WiMAX – based network and evaluate the performance for quality of service (QoS) using an idea of IEEE 802.16 technology. In our models, the study used a multiprocessor architecture organized by the interconnection network. OPNET Modeler is used to simulate the architecture and to calculate the performance criteria (i.e. throughput, delay and data dropped) that
slightly concerned in network estimation. It is concluded that our models shorten the time quite a bit for
obtaining the performance measures of an end-to-end delay as well as throughput can be used as an
effective tool for this purpose.
A SURVEY ON DIFFERENT TYPES OF CLUSTERING BASED ROUTING PROTOCOLS IN WIRELESS...Journal For Research
In most of today’s application the wireless sensor network (WSN) play an important role.WSN is an autonomous system to monitor physical and environmental conditions. It can sense and compute the information or data or message that transmitted through it. Important design issue of the Wireless sensor networks energy consumption and lifetime of the network. The design of different routing protocol is another important design issue in WSN. There are mainly broad types of routing protocols in wireless sensor networks. This paper mainly deals with different types of cluster based routing protocols in WSN. Clustering algorithms are mainly defined to reduce the energy consumption and improves the life time of the network.
Energy efficient cluster-based service discovery in wireless sensor networksambitlick
1) The document proposes an energy-efficient service discovery protocol for wireless sensor networks that exploits a cluster-based network overlay.
2) Clusterhead nodes form a distributed service registry to minimize communication costs during service discovery and maintenance.
3) The performance of the proposed integrated clustering and service discovery solution is evaluated through simulations under different network conditions.
The document proposes an energy-efficient service discovery protocol for wireless sensor networks. It uses a lightweight clustering algorithm to build a distributed directory of service registrations. Each cluster head maintains information about services in its cluster. The protocol aims to minimize communication costs during service discovery and maintenance of the distributed directory. It constructs disjoint tree clusters where high-capability nodes become cluster heads and advertise their roles, while other nodes select parents based on capability grades.
Onder het mom van COREPER worden door de Europese Unie diverse snoepreisjes georganiseerd. OPvallend is dat de leden van COREPER hun partner kunnen meenemen op een dergelijke snoepreis.
Hoe rijk is eurocommissaris Marianne Thyssen?Thierry Debels
Nieuwbakken eurocommissaris Marianne Thyssen moet een verklaring afleggen over haar vermogen. Uit dat document blijkt dat ze een aanzienlijk roerend en onroerend vermogen heeft.
An efficient hybrid peer to-peersystemfordistributeddatasharingambitlick
The document proposes a hybrid peer-to-peer system that combines the advantages of structured and unstructured networks. It consists of two parts: 1) a structured core network that forms the backbone and provides efficient data lookup; 2) multiple unstructured networks attached to each core node, allowing flexible peer joining/leaving. This two-tier design decouples efficiency and flexibility. Simulation results show the hybrid system balances these properties better than single-approach networks.
Admission control and routing in multi hop wireless networksambitlick
This document summarizes a research paper about admission control and routing algorithms for multi-hop wireless networks that provide quality of service guarantees for flows requesting a pre-specified bandwidth. The paper develops an optimal admission control and routing algorithm that has performance close to an offline algorithm with complete future knowledge. The algorithm makes no assumptions about flow arrival patterns and can be implemented in a distributed manner. It also proves this algorithm is asymptotically optimal with respect to competitive ratio, a metric that measures performance compared to an offline algorithm. Finally, the paper discusses how the algorithm can be modified to allow use of standard shortest-path algorithms for distributed implementation.
Stichting van Jacques van Ypersele kreeg geld van rijke AmerikanenThierry Debels
Op 24 september 2013 richt Jacques van Ypersele de stichting Centres Ste-Thérèse op.
Uit een officieel document van de VS blijkt dat de stichting een geldsom kreeg van rijke Amerikaanse geldschieters.
Het gaat meer bepaald om The Stephen F & Camilla T Brauer Charitable Trust.
Hieruit blijkt dat Van Ypersele nog steeds erg goede relaties onderhoudt met onderdanen uit de Verenigde Staten.
Architecture for reliable service discoveryambitlick
The authors provide an overview of standardized service discovery and delivery solutions for mobile ad hoc networks (MANETs). They propose a novel architecture that allows selecting a service provider based on metrics like the power supply of the provider and the path to the destination. This architecture is based on a decentralized approach using Service Location Protocol (SLP) extensions. It aims to provide reliable service discovery and delivery in MANETs by considering energy constraints affecting the network topology and connectivity.
1) This document proposes a new anomaly detection scheme for mobile ad hoc networks (MANETs) based on dynamic learning.
2) The scheme uses a statistical decision theory to calculate projection distances between the current and normal states of nodes using weighted coefficients and a forgetting curve.
3) Simulations evaluate the scheme's effectiveness in detecting five types of attacks on the ad hoc on-demand distance vector (AODV) routing protocol for MANETs of different sizes.
On Multihop Distances in Wireless Sensor Networks with Random Node Locationsambitlick
The document analyzes the distribution of maximum multihop distances in wireless sensor networks with random node locations. It proposes a greedy method to maximize the multihop distance in 2D networks by restricting propagation direction outward from the source in each hop and searching for the furthest neighbor. This differs from prior work modeling 1D networks that used a Gaussian distribution, which is shown to not accurately model 2D distances. The paper transforms the Gamma distribution to effectively approximate maximum distances in 2D and provides a more consistent representation of the multihop distance distribution compared to the Gaussian model. It derives the expected value and standard deviation of distances using the Gamma approximation and compares to simulation results.
The document lists 23 networking and mobile computing projects implemented in NS2. It includes projects on topics like mobility in wireless networks, intrusion detection, neighbor discovery, energy renewal with wireless power transfer, load balancing, and spectrum access control. Contact information is provided for those interested in the project reports, presentations, source code, or implementing new projects.
TCP Fairness for Uplink and Downlink Flows in WLANsambitlick
The document discusses simulation parameters for a wireless network simulation in NS2 including the simulator used, simulation time, packet interval, background data traffic types, packet size, transmission range, routing protocol, and MAC protocol. It also briefly discusses queue management for wireless networks and how it differs from wired networks by not being visible. Client-server computing and networking is defined as well as packet scheduling policies and comparing FIFO to RENO scheduling. Bandwidth sharing approaches are examined for heterogeneous congestion control protocols. Finally, end-to-end throughput is defined and its decrease with more nodes in a chain topology is explained due to relaying overhead at intermediate nodes.
A collaborative wireless sensor network routingambitlick
This document proposes a new routing scheme called node reliance for wireless sensor networks. Node reliance rates how much each node is relied upon for routing data from sources to sinks. Sources will route through nodes with low reliance ratings to avoid overusing critical nodes and maximize network lifetime. The scheme is evaluated using an example network and compared to other routing methods. Node reliance aims to reduce energy waste from disconnected sources by encouraging collaboration between sources in path selection.
Waarom proces van Delphine wellicht met sisser aflooptThierry Debels
Op 23 september 2014 wordt het proces van Delphine Boël verdergezet. Hierop krijgt de rechtbank een maand de tijd om een uitspraak te doen. Tegen deze uitspraak kan vervolgens door alle partijen hoger beroep aangetekend worden.
De rechtszaak met dossiernummer 2013 / A / 9225 bevat enkele merkwaardige elementen.
Jean-Jacques De Gucht heeft een passie voor kunst. In interviews heeft hij al eens gezegd dat hij er stiekem van droomt om galeriehouder te worden.
Die droom heeft hij nu waargemaakt. In het voorjaar van 2014 heeft De Gucht met zijn echtgenote de bvba De filatuur opgericht, een kunstgalerie.
Towards the Performance Analysis of IEEE 802.11 in Multi-hop Ad-Hoc Networksambitlick
This document proposes analytical models to analyze the performance of the IEEE 802.11 protocol under unsaturated traffic conditions in multi-hop wireless networks. It presents a two-dimensional Markov chain model to describe the behavior of IEEE 802.11 under different offered traffic loads, showing the effect of load on transmission probability. It also proposes a three-dimensional model to describe multi-hop 802.11 networks, modeling not only data sources but also relay stations forwarding traffic. The models are validated through ns-2 simulations with different network configurations for metrics like throughput, delay, queue length, and energy consumption.
History based adaptive backoff (hbab) ieee 802.11 mac protocolambitlick
The document proposes a History-Based Adaptive Backoff (HBAB) MAC protocol to modify the IEEE 802.11 backoff algorithm. The standard IEEE 802.11 protocol uses a binary exponential backoff algorithm that resets the contention window size to the minimum after a successful transmission, which can lead to repeated collisions. HBAB instead slowly increases and decreases the contention window size based on the busyness of the channel, similar to adaptive delta modulation used in communications. Simulations show HBAB provides around 15% higher packet delivery fraction and up to 50% lower average packet delay compared to the standard backoff algorithm.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Performance analysis and evaluation of IEEE 802.11 distributed coordination f...journalBEEI
This paper discusses the distributed coordination function (DCF) access mechanism which is a carrier sense multiple access with collision avoidance (CSMA/CA) scheme. Simulation projects for different DCF performance parameters have been built using the OPNET network simulator. The projects are mainly basic service set (BSS) topology simulated under different parameter values (data rate, fragmentation, RTS/CTS, number of nodes, and load condition). Simulation results show when the DCF access mechanism is better under what load condition, and how to choose the best fragmentation threshold and other access-mechanism specific parameters according to the network conditions. Simulation results were validated against a theoretically calculated maximum throughput (the simulation maximum throughput was about 70% of the theoretically calculated maximum throughput).
General Model for Single and Multiple Channels WLANs with Quality of Service...ijwmn
In this paper we develop an intergraded model for request mechanism and data transmission in the uplink
phase in the presence of channel noise. This model supports quality of service. The wireless channel is prone
to many impairments. Thus, certain techniques have to be developed to deliver data to the receiver. We
calculated the performance parameters for single and multichannel wireless networks, like the requests
throughput, data throughput and the requests acceptance probability and data acceptance probability. The
proposed model is general model since it can be applied to different wireless networks such as IEEE802.11a,
IEEE802.16e, CDMA operated networks and Hiperlan\2.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
QOS CATEGORIES ACTIVENESS-AWARE ADAPTIVE EDCA ALGORITHM FOR DENSE IOT NETWORKSIJCNCJournal
IEEE 802.11 networks have a great role to play in supporting and deploying of the Internet of Things (IoT). The realization of IoT depends on the ability of the network to handle a massive number of stations and transmissions and to support Quality of Service (QoS). IEEE 802.11 networks enable the QoS by applying the Enhanced Distributed Channel Access (EDCA) with static parameters regardless of existing network capacity or which Access Category (AC) of QoS is already active. Our objective in this paper is to improve the efficiency of the uplink access in 802.11 networks; therefore we proposed an algorithm called QoS Categories Activeness-Aware Adaptive EDCA Algorithm (QCAAAE) which adapts Contention Window (CW) size, and Arbitration Inter-Frame Space Number (AIFSN) values depending on the number of associated Stations (STAs) and considering the presence of each AC. For different traffic scenarios, the simulation results confirm the outperformance of the proposed algorithm in terms of throughput (increased on average 23%) and retransmission attempts rate (decreased on average 47%) considering acceptable delay for sensitive delay services.
EFFECTS OF MAC PARAMETERS ON THE PERFORMANCE OF IEEE 802.11 DCF IN NS-3ijwmn
This paper presents the design procedure of the NS-3 script for WLAN that is organized according to the hierarchical manner of TCP/IP model. We configure all layers by using NS-3 model objects and set and modify the values used by objects to investigate the effects of MAC parameters (access mechanism, CWmin, CWmax and retry limit) on the performance metrics viz. packet delivery ratio, packet lost ratio, aggregated throughput, and average delay. The simulation results show that RTS/CTS access mechanism outperforms basic access mechanism in saturated state, whereas the MAC parameters have no significant impact on network performance in non-saturated state. A higher value of CWmin improves the aggregated throughput in expense of average delay. The tradeoff relationships among the performance metrics are also observed in results for the optimal values of MAC parameters. Our design procedure represents a good guideline for new NS-3 users to design and modify script and results greatly benefit the network design and management.
Efficient and Fair Bandwidth Allocation AQM Scheme for Wireless NetworksCSCJournals
Heterogeneous Wireless Networks are considered nowadays as one of the potential areas in research and development. The traffic management’s schemes that have been used at the fusion points between the different wireless networks are classical and conventional. This paper is focused on developing a novel scheme to overcome the problem of traffic congestion in the fusion point router interconnected the heterogeneous wireless networks. The paper proposed an EF-AQM algorithm which provides an efficient and fair allocation of bandwidth among different established flows. Finally, the proposed scheme developed, tested and validated through a set of experiments to demonstrate the relative merits and capabilities of a proposed scheme
This document summarizes a research paper that evaluates the performance of wired and wireless local area networks using simulation. It describes simulating Ethernet and IEEE 802.11 wireless LANs in OPNET with varying numbers of users. Key performance metrics for wired networks like collision count, throughput, and delay were analyzed. For wireless, metrics like data dropped, throughput, and access delay were studied. As the number of users increased, throughput decreased more for wireless than wired due to transmission limitations in wireless. The paper concludes wireless performs better than wired for small user numbers but degrades more with increasing loads.
A NOVEL SLOTTED ALLOCATION MECHANISM TO PROVIDE QOS FOR EDCF PROTOCOLIAEME Publication
The IEEE 802.11e EDCF mechanism cannot guarantee the QOS of high-priority traffic as the bandwidth consumption of the low-priority traffic increases. Also, in the presence of high priority traffic dampen link utilization of low priority traffic. To overcome these problems, we propose the Novel mechanism in our research that extends IEEE 802.11e EDCF by introducing a Super Slot and Virtual Collision. Compared to EDCF, our proposed approach has EDCF has two advantages: (a) Higher priority traffic achieves Quality of service regardless of the amount of low priority traffic, and (b) Low priority traffic obtains a higher throughput in the presence of same amount of high priority traffic.
Performance Analysis of MAC Layer Protocols for WSN with Considering the Effe...BRNSSPublicationHubI
This document summarizes a research article that analyzed the performance of three MAC layer protocols (IEEE 802.11, IEEE 802.15.4, and TDMA) in a wireless sensor network considering the effects of the hidden node problem. Six performance metrics were evaluated: goodput, throughput, packet delivery ratio, residual energy, average delay, and node lifetime. The results showed that TDMA provided the best energy conservation and highest delay, while IEEE 802.11 gave the best throughput and goodput as well as lowest delay. IEEE 802.15.4 and TDMA were better than IEEE 802.11 at mitigating the hidden node problem.
ANALYSIS OF LINK STATE RESOURCE RESERVATION PROTOCOL FOR CONGESTION MANAGEMEN...ijgca
With the wide spread of WiFi hotspots, concentrated traffic workload on Smart Web (SW) can slow down the network performance. This paper presents a congestion management strategy considering real time activities in today’s smart web. With the SW context, cooperative packet recovery using resource reservation procedure for TCP flows was adapted for mitigating packet losses. This is to maintain data consistency between various access points of smart web hotspot. Using a real world scenario, it was confirmed that generic TCP cannot handle traffic congestion in a SW hotspot network. With TCP in scalable workload environments, continuous packet drops at the event of congestion remains obvious. This is unacceptable for mission critical domains. An enhanced Link State Resource Reservation Protocol (LSRSVP) which serves as dynamic feedback mechanism in smart web hotspots is presented. The contextual behaviour was contrasted with the generic TCP model. For the LS-RSVP, a simulation experiment for TCP connection between servers at the remote core layer and the access layer was carried out while using selected benchmark metrics. From the results, under realistic workloads, a steady-state throughput response was achieved by TCP LS-RSVP to about 3650Bits/secs compared with generic TCP plots in a previous study. Considering network service availability, this was found to be dependent on fault-tolerance of the hotspot network. From study, a high peak threshold of 0.009 (i.e. 90%) was observed. This shows fairly acceptable service availability behaviour compared with the existing TCP schemes. For packet drop effects, an analysis on the network behaviour with respect to the LS-RSVP yielded a drop response of about 0.000106 bits/sec which is much lower compared with the case with generic TCP with over 0.38 bits/sec. The latency profile of average FTP download response was found to be 0.030secs, but with that of FTP upload response, this yielded about 0.028 sec. The results from the study demonstrate efficiency and optimality for realistic loads in Smart web contexts.
Analysis of Link State Resource Reservation Protocol for Congestion Managemen...ijgca
With the wide spread of WiFi hotspots, concentrated traffic workload on Smart Web (SW) can slow down
the network performance. This paper presents a congestion management strategy considering real time
activities in today’s smart web. With the SW context, cooperative packet recovery using resource
reservation procedure for TCP flows was adapted for mitigating packet losses. This is to maintain data
consistency between various access points of smart web hotspot. Using a real world scenario, it was
confirmed that generic TCP cannot handle traffic congestion in a SW hotspot network. With TCP in
scalable workload environments, continuous packet drops at the event of congestion remains obvious. This
is unacceptable for mission critical domains. An enhanced Link State Resource Reservation Protocol (LSRSVP)
which serves as dynamic feedback mechanism in smart web hotspots is presented. The contextual
behaviour was contrasted with the generic TCP model. For the LS-RSVP, a simulation experiment for TCP
connection between servers at the remote core layer and the access layer was carried out while using
selected benchmark metrics. From the results, under realistic workloads, a steady-state throughput
response was achieved by TCP LS-RSVP to about 3650Bits/secs compared with generic TCP plots in a
previous study. Considering network service availability, this was found to be dependent on fault-tolerance
of the hotspot network. From study, a high peak threshold of 0.009 (i.e. 90%) was observed. This shows
fairly acceptable service availability behaviour compared with the existing TCP schemes. For packet drop
effects, an analysis on the network behaviour with respect to the LS-RSVP yielded a drop response of about
0.000106 bits/sec which is much lower compared with the case with generic TCP with over 0.38 bits/sec.
The latency profile of average FTP download response was found to be 0.030secs, but with that of FTP
upload response, this yielded about 0.028 sec. The results from the study demonstrate efficiency and
optimality for realistic loads in Smart web contexts.
A dynamic performance-based_flow_controlingenioustech
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Dcf learn and performance analysis of 802.11 b wireless networkIJCNCJournal
Though WLAN wireless network has been widely deployed as the main split-flow deployment of the
communication network, little study emphasizes its performance as WLAN protocols were only designed for
the public communicating conveniently with each other. Actually that too much wireless access points
assembling together will cause self-interference to the whole WLAN network. This paper investigates the
distributed coordination function (DCF) learn and the performance study of 802.11b networks. Firstly, our
study illustrates the performance of its MAC layer and its fairness issues related to DCF. Next we propose
the details which should be paid attention to in deploying network services. Then, performance analyses
are evaluated by simulation and real test for a dense wireless network. Our main goal is to give proposals
to network operators how to design a WLAN network more standardized and orderly.
Performance evaluation of the IEEE 802.11n random topology WLAN with QoS appl...IJECEIAES
The IEEE 802.11n supports high data rate transmissions due its physical layer Multiple Input Multiple Output (MIMO) advanced antenna system and MAC layer enhancement features (frame aggregation and block acknowledgement). As a result this standard is very suitable for multimedia services through its Enhanced Distributed Channel Access (EDCA). This paper focuses on evaluating the Quality of Service (QoS) application on the performance of the IEEE 802.11n random topology WLAN. Three different number of nodes (3, 9 and 18) random topology with one access point are modeled and simulated by using the Riverbed OPNET 17.5 Modular to investigate the Wireless Local Area Network (WLAN) performance for different spatial streams. The result clarified the impact of QoS application and showed that its effect is best at the 18 node number topology. For a 4x4 MIMO, when QoS is applied and with respect to the no QoS application case, simulation results show a maximum improvement of 86.4%, 33.9%, 52.2% and 68.9% for throughput, delay, data drop and retransmission attempts, respectively.
TCP Fairness for Uplink and Downlink Flows in WLANsambitlick
The document proposes a dual queue scheme at access points to improve fairness between uplink and downlink TCP flows in wireless local area networks. The scheme employs two queues - one for downlink TCP data packets and another for uplink TCP ACK packets. By selecting the queues with different probabilities, the access point can control the ratio of TCP data and ACK sending rates to achieve fairness. Simulation results show that the dual queue scheme is effective at resolving the unfairness problem in a simple way without modifying existing MAC protocols or requiring per-flow queueing.
A Cross Layer Based Scalable Channel Slot Re-Utilization Technique for Wirele...csandit
Due to tremendous growth of the wireless based application services are increasing the demand
for wireless communication techniques that use bandwidth more effectively. Channel slot reutilization
in multi-radio wireless mesh networks is a very challenging problem. WMNs have
been adopted as back haul to connect various networks such as Wi-Fi (802.11), WI-MAX
(802.16e) etc. to the internet. The slot re-utilization technique proposed so far suffer due to high
collision due to improper channel slot usage approximation error. To overcome this here the
author propose the cross layer optimization technique by designing a device classification
based channel slot re-utilization routing strategy which considers the channel slot and node
information from various layers and use some of these parameters to approximate the risk
involve in channel slot re-utilization in order to improve the QoS of the network. The simulation
and analytical results show the effectiveness of our proposed approach in term of channel slot
re-utilization efficiency and thus helps in reducing latency for data transmission and reduce
channel slot collision.
Similar to A novel pause count backoff algorithm for channel access (20)
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This document lists 15 potential 2013 IEEE NS2 project titles related to wireless networks and sensor networks. It includes projects on topics like capacity of hybrid wireless mesh networks, delay-optimal broadcast in multihop wireless networks, detection of spoofing attackers, and harvesting-aware energy management for wireless sensor networks. The document provides contact information for a company called Ambitlick Solutions that offers support and deliverables for IEEE projects, including project abstracts, papers, presentations, reports, and certification.
This document lists over 40 potential 2013 IEEE Java Dotnet project titles across various domains including wireless networks, mobile computing, network security, data mining, cloud computing, parallel and distributed computing, and multimedia/image processing. The projects focus on technical topics such as wireless sensor networks, wireless mesh networks, cognitive radio networks, mobile ad hoc networks, network coding, video streaming, machine learning, data warehousing, and more. Project deliverables include an abstract, IEEE paper, presentation, report, working prototype or proof of concept, and certification. Bulk older and new projects can be provided at a low cost.
Handling selfishness in replica allocationambitlick
The document discusses techniques for handling selfish nodes in replica allocation over mobile ad hoc networks. It aims to reduce traffic overhead while maintaining high data accessibility. The techniques include a selfish node detection algorithm that considers partial selfishness and novel replica allocation methods to address issues caused by selfish nodes hoarding replicas for their own benefit instead of sharing memory space. Simulations are used to evaluate the performance of these techniques in improving data delivery rates.
Mutual Distance Bounding Protocols enable entities to determine an upper bound on their physical distance and authenticate each other. They have been actively researched due to distance-based attacks on wireless systems like RFID. While most protocols provide unilateral authentication of a tag to a reader, one was proposed to provide mutual authentication with a lower false acceptance rate. However, this analysis is shown to overestimate security, as a new attack achieves a higher false acceptance rate. A method is also introduced to modify existing unilateral authentication protocols into mutual authentication protocols.
Moderated group authoring system for campus wide workgroupsambitlick
This paper describes a distributed authoring system for campus workgroups that allows group members to modify any document type using their own devices. Each member maintains an updatable copy of shared content, and read-only copies are distributed asynchronously based on wireless availability. Group members manually reconcile updates through moderation, merging changes from others into their copy. Over time, successive moderation converges all copies into a single version. An evaluation found the asynchronous update model effective and the moderation process intuitive for students.
Efficient spread spectrum communication without pre shared secretsambitlick
This document proposes a new mechanism called Time Reversed Message Extraction and Key Scheduling (TREKS) that allows for efficient spread spectrum communication without pre-shared secrets. TREKS is four orders of magnitude faster than previous solutions to this problem. It enables long-term spread spectrum communication with optimal energy costs, minimal storage overhead, and a computation cost at most twice traditional spread spectrum. The approach was evaluated through simulations and experiments sustaining 1Mbps communication spread over 100 Megachips per second using modest hardware.
Adaptive weight factor estimation from user review 1ambitlick
This document proposes a novel technique called Adjacent Pair Priorities (APP) to estimate weight factors for quality of service parameters in vertical handoff decision algorithms. The APP technique allows users to set relative priority levels for adjacent pairs of QoS parameters in descending order using an exponential mapping. This adaptive approach controls the width of the weight distribution to provide flexibility for users. The document outlines the system requirements, block diagram, modules and references several research papers on vertical handoff decision schemes and network selection algorithms.
The document proposes an Integrated Institutional Portal that allows all colleges and institutions within a university or district to share information. [1] The portal would allow students and staff from different colleges to discuss and request information from one another through blogs, forums and by publishing notices. [2] Currently, each college maintains separate portals without a common forum for communication. [3] The proposed centralized portal managed by a super administrator would make all college information like results, events and departments accessible to benefit students and staff across institutions.
This document describes an Embassy Administration portal that aims to centralize and automate manual processes at a college. [1] The portal allows separate login access for staff, parents, students and other members of the college. [2] It displays student results, attendance, and performance for parents to view as well as enables communication between parents and faculty. [3] The system conducts model and unit examinations.
The document proposes a customer relationship management system (CRMS) to help space marketing executives, managers, and management interact and share information online. The existing CRMS is manual and DOS-based, which has disadvantages like a distributed database, obsolete technology, and low efficiency. The proposed system is a web-based online CRMS designed for the space marketing department. It allows monitoring executive calls, tracking performance, and sharing information among departments to improve customer relationships and business operations. The system has modules for corporate administration, regional management, center management, and executives to organize work and monitor progress at different levels.
Mutual Distance Bounding Protocols enable entities to determine an upper bound on their physical distance and authenticate each other. They have been actively researched due to distance-based attacks on wireless systems like RFID. While most protocols provide unilateral authentication of a tag to a reader, one was proposed to provide mutual authentication with a lower false acceptance rate. However, this analysis is shown to overestimate security, as a new attack achieves a higher false acceptance rate. A method is also introduced to modify existing unilateral authentication protocols into mutual authentication protocols.
Moderated group authoring system for campus wide workgroupsambitlick
This paper describes a distributed authoring system for campus workgroups that allows group members to modify any document type using their own devices. Each member maintains an updatable copy of shared content, and read-only copies are distributed based on wireless availability. Group members manually reconcile updates through moderation, merging changes from others into their copy. Over time, successive moderations converge the multiple versions into a single version. An evaluation found the asynchronous update propagation and moderation process intuitive for students.
Efficient spread spectrum communication without pre shared secretsambitlick
This document proposes a new mechanism called Time Reversed Message Extraction and Key Scheduling (TREKS) that allows for efficient spread spectrum communication without pre-shared secrets. TREKS is four orders of magnitude faster than previous solutions to this problem and enables long-term spread spectrum communication without establishing keys. It was evaluated through simulation and on a testbed and can sustain 1Mbps communication spread over a 100 Megachips bandwidth in real-time, with provably optimal energy cost and minimal storage overhead.
Comments on “mabs multicast authentication based on batch signature”ambitlick
This document summarizes and critiques the MABS-DSA protocol proposed by Zhou et al. for multicast authentication using batch verification. While MABS-DSA was intended to increase efficiency and security over other implementations, the author finds through reexamination of the arithmetic that the algorithm is actually incorrect and batch signature verification would fail almost always, even when individual packets were properly signed by an honest sender. The key issue is a flaw in protocol correctness rather than the intended security improvements.
Energy-Efficient Protocol for Deterministic and Probabilistic Coverage In Sen...ambitlick
The document proposes a new probabilistic coverage protocol (PCP) for sensor networks that can employ different sensing models. PCP aims to address the costly task of designing and testing different coverage protocols for each sensing model. It works with common disk sensing models as well as probabilistic sensing models with minimal changes. Simulation results show that PCP outperforms other deterministic and probabilistic protocols in terms of number of activated sensors, total energy consumed, and network lifetime while being robust against failures and inaccuracies.
Energy efficient protocol for deterministicambitlick
The document describes a new probabilistic coverage protocol (PCP) for sensor networks that can employ both deterministic and probabilistic sensing models. PCP works by activating sensors to construct an approximate triangular lattice over the monitored area. It is more energy efficient than previous protocols by reducing the number of activated sensors needed for coverage. Simulation results show PCP outperforms other protocols in terms of energy consumption and network lifetime while maintaining coverage under various conditions.
Estimating Parameters of Multiple Heterogeneous Target Objects Using Composit...ambitlick
This article proposes a method for estimating parameters of multiple heterogeneous target objects (objects with different sizes and shapes) using networked binary sensors. The sensors are simple and only report detections, but no individual sensor location is known. The method introduces "composite sensor nodes" containing multiple sensors in a fixed arrangement. This provides relative location information to help distinguish individual target objects. As an example, the article considers a composite node with two sensors on a line segment. Measures from these nodes can identify target shapes and estimate object parameters like radius and side lengths. Numerical tests demonstrate networked composite sensors can estimate parameters of multiple target objects.
A Privacy-Preserving Location Monitoring System for Wireless Sensor Networksambitlick
This document proposes a privacy-preserving location monitoring system for wireless sensor networks. The system uses two in-network location anonymization algorithms:
1) A resource-aware algorithm that aims to minimize communication and computational costs by having each sensor node find a cloaked area containing at least k persons and report only aggregate location information.
2) A quality-aware algorithm that aims to maximize accuracy by iteratively refining cloaked areas reported by the resource-aware algorithm to minimize their size, while still maintaining k-anonymity.
The system collects anonymous aggregate location information to build a spatial histogram for estimating person distributions and answering queries about aggregate locations, while preserving individuals' location privacy against potential attacks from untrusted
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Main Java[All of the Base Concepts}.docxadhitya5119
This is part 1 of my Java Learning Journey. This Contains Custom methods, classes, constructors, packages, multithreading , try- catch block, finally block and more.
How to Make a Field Mandatory in Odoo 17Celine George
In Odoo, making a field required can be done through both Python code and XML views. When you set the required attribute to True in Python code, it makes the field required across all views where it's used. Conversely, when you set the required attribute in XML views, it makes the field required only in the context of that particular view.
Beyond Degrees - Empowering the Workforce in the Context of Skills-First.pptxEduSkills OECD
Iván Bornacelly, Policy Analyst at the OECD Centre for Skills, OECD, presents at the webinar 'Tackling job market gaps with a skills-first approach' on 12 June 2024
Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) CurriculumMJDuyan
(𝐓𝐋𝐄 𝟏𝟎𝟎) (𝐋𝐞𝐬𝐬𝐨𝐧 𝟏)-𝐏𝐫𝐞𝐥𝐢𝐦𝐬
𝐃𝐢𝐬𝐜𝐮𝐬𝐬 𝐭𝐡𝐞 𝐄𝐏𝐏 𝐂𝐮𝐫𝐫𝐢𝐜𝐮𝐥𝐮𝐦 𝐢𝐧 𝐭𝐡𝐞 𝐏𝐡𝐢𝐥𝐢𝐩𝐩𝐢𝐧𝐞𝐬:
- Understand the goals and objectives of the Edukasyong Pantahanan at Pangkabuhayan (EPP) curriculum, recognizing its importance in fostering practical life skills and values among students. Students will also be able to identify the key components and subjects covered, such as agriculture, home economics, industrial arts, and information and communication technology.
𝐄𝐱𝐩𝐥𝐚𝐢𝐧 𝐭𝐡𝐞 𝐍𝐚𝐭𝐮𝐫𝐞 𝐚𝐧𝐝 𝐒𝐜𝐨𝐩𝐞 𝐨𝐟 𝐚𝐧 𝐄𝐧𝐭𝐫𝐞𝐩𝐫𝐞𝐧𝐞𝐮𝐫:
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Strategies for Effective Upskilling is a presentation by Chinwendu Peace in a Your Skill Boost Masterclass organisation by the Excellence Foundation for South Sudan on 08th and 09th June 2024 from 1 PM to 3 PM on each day.
This document provides an overview of wound healing, its functions, stages, mechanisms, factors affecting it, and complications.
A wound is a break in the integrity of the skin or tissues, which may be associated with disruption of the structure and function.
Healing is the body’s response to injury in an attempt to restore normal structure and functions.
Healing can occur in two ways: Regeneration and Repair
There are 4 phases of wound healing: hemostasis, inflammation, proliferation, and remodeling. This document also describes the mechanism of wound healing. Factors that affect healing include infection, uncontrolled diabetes, poor nutrition, age, anemia, the presence of foreign bodies, etc.
Complications of wound healing like infection, hyperpigmentation of scar, contractures, and keloid formation.
2. of transmissions and system load may have a positive expected before the ACK timeout timer, otherwise the
correlation but is not sufficient to precisely set CW sender will consider this frame as lost and retransmits
value. As a result, such an imprecise calculation of CW it. For each failed transmission, the station doubles its
size for stations introduces a fairness issue. current CW size until CW reaches its maximum value
In this work, we propose a new method to estimate (CWmax) (the default value of CWmax is 1024 in IEEE
the number of active stations and find an appropriate 802.11b). The station then performs the backoff
value of CW within a wireless network. The procedure again and reduces the probability of
countdown procedure in backoff mode is paused when collision in the next transmission by using a larger CW
other stations use the wireless channel at the same (CWnew). After a successful transmission, the CW is
time. Therefore, each pause represents more than one reset to the initial value (CWmin), which is equal to 32
station using the wireless channel and the number of in IEEE 802.11b.
pauses could give a sense of the system status. The
proposed method, known as Pause Count Backoff
(PCB), counts pauses during the countdown procedure
and sets an appropriate CW size for the current
condition. Using simulation results, we show that the
proposed method improves system utilization and
reduces the end-to-end delay when compared with
other previous schemes such as the Distributed
Coordination Function (DCF), Exponential Increase
Exponential Decrease (EIED), and Adaptive Enhanced
Distributed Coordination Function (AEDCF) Figure 1 Illustration of the CSMA/CA mechanism
algorithms. The fairness index of PCB is 2.2 Related Backoff Algorithms
approximately 1 in most of the network simulation
scenarios. The size of the contention window in the backoff
This paper is organized as follows. Section 2 procedure can affect the overheads for network access
describes the DCF function and discusses the channels with contentions. A large CW results in a
overheads of transmissions in wireless channel. Brief long idle duration when there are only a few active
reviews of related studies are presented in section 2. In stations in the system (although a large CW could lead
section 3, we describe our proposed PCB algorithm. to a lower collision rate). A small CW can enhance the
Simulation results and a performance analysis of our channel utilization but the number of collisions could
proposed PCB algorithm are discussed in section 4. increase quickly if a small CW is used for many active
Finally, section 5 concludes the paper and presents stations. Thus, the backoff algorithm should adapt the
future works. correct value of CW to fit the system status. Many past
research efforts on enhanced algorithms have been
2. Background and Related work proposed taking into account various considerations
such as throughput maximization [5] and QoS
2.1 IEEE 802.11 DCF Algorithm requirements [6].
In In [5], a scheme named EIED has been proposed, the
Based on the 802.11 standard, DCF adopts a station sets the new contention window CWnew as
CSMA/CA mechanism. In this algorithm, each station CWold multiplied by the parameter ri, (where ri is the
needs to sense a wireless channel before sending increment backoff factor) as a successful transmission.
frames. Transmission is performed if the medium is When a collision occurs, a new value of CW is given
idle for a Distributed InterFrame Space (DIFS) period by CWold divided by the parameter rd where rd is the
as shown in Figure 1a – otherwise the backoff decrement backoff factor. The advantage of
procedure is activated. A backoff number is chosen exponential increase is that Exponential Increase (EI)
randomly from the interval [0,CW-1]. The backoff can reduce the probability of continuous collided
number is decremented by one for every idle timeslot frames when many stations contend a channel
during the countdown procedure. The station sends out concurrently. Moreover, ED (Exponential Decrease)
frames when the backoff number is counted down to keeps the collision history of the previous
zero as shown in Figure 1b. This frame may collide transmissions instead of resetting automatically to
with other frames or be discarded due to wireless error CWmin. ED could prevent numerous collisions from
during the transmission. To indicate a successful occurring, especially in a network with large number of
transmission, an acknowledgement from the receiver is stations. In [6], the authors propose an adaptive service
differentiation algorithm for IEEE 802.11 WLANs. In
164
3. AEDCF each station calculates the collision rate it pauses during the countdown procedure in step 1 could
experiences during a given interval. A high collision observe the number of active stations in the system. In
rate often indicates a small CW under heavy system Figure 2, node A observes three pauses during its
loading. In AEDCF, a station does not reset the CW backoff procedure. From the observation, node A
after a successful transmission. The station sets a new paused resume paused resume paused
CW based on the current collision rate. In AEDCF, the node A backoff window
time
authors seek to determine the optimal size of the CW
that will minimize collisions and improve the system node B time
efficiency. The accuracy of the estimated system status node C time
determines whether the CW of the proposed backoff
algorithm is appropriate or not. In prior approaches, node D time
these algorithms estimate the system load from the Figure 2 Estimating number of active stations with the
number of collisions encountered. This is inadequate paused backoff counter
because the station only observes its own transmission determines that there are more than three mobile
status which does not represent the whole system stations concurrently contending for the wireless
condition. The imprecise information affects fairness channel. To keep the scheme stable, Exponential
among stations. In EIED and AEDCF algorithms, a Weighted Moving Average (EWMA) is applied to
station may inaccurately assign a small CW for a calculate an average pause count. The number of
highly contended channel. This will result in this pauses observed directly correlates to the backoff
station having a higher channel access opportunity than counter value. A high backoff counter records more
other stations. When the station with a small CW pauses than a small backoff counter during the
collides with others, the station will set the CW to a countdown procedure. We propose the solution by
small value once again due to the small CW used in the setting CW size to active stations in step 2. In step 2, a
last transmission and a lower collision rate. policy with successful transmission results sets the
proper contention window size for the backoff
3. Pause Count Backoff (PCB) Algorithm procedure. While transmission is a success, CW is set
to the average pause value multiplied by β which
The main objective of our proposed algorithm is to relates to the collision rate. The method used to
improve the system performance of DCF with fairness compute β is given below:
into consideration as well. Previous efforts have 2N (1)
Pc ≅
focused on improving system efficiency by adjusting CW
the size of CW from transmission results obtained. β = 1 / Pc (2)
Although the transmission result correlates with the Pc represents the probability of collision for each
system status, it cannot precisely determine the system transmission in a station. N is the number of active
status from a partial transmitting event. Inaccurate stations in the system. The new CW size can be
estimation results in inefficiency and unfairness among derived from the number of active stations and β (as
stations. Thus, our proposed PCB algorithm takes shown above). To minimize oscillations in the pause
global observations to estimate the system status, and count, the new CW is applied after an observation
then PCB sets an appropriate CW that matches the period which is determined by the number of
global system status. There are two steps in our transmission attempts. In this paper, we set the
proposed PCB algorithm. The first step is the observation period to 10 transmission attempts in the
estimation of CW and the second step involves setting station. PCB sets a proper contention window size
CW. according to the system status when transmission is
In step 1 of our proposed PCB approach, a method successful instead of resetting CW to CWmin
estimates the number of active stations. In DCF, the immediately or additively/ multiplicatively decreasing
backoff counter pauses if other stations transmit frames CW by a single transmission status. When transmission
at the same time and resumes countdown whilst a fails, the new CW should prevent further collisions in
channel is idle for a DIFS period. The concept is the next transmission to reduce the overhead of
illustrated in Figure 2. The proposed method observes retransmissions. In our proposed PCB algorithm, the
the number of pauses until the counter becomes zero. station sets a new CW to a large contention window to
Each pause represents another station transmitting its avoid further collisions. The station could avoid the
frames or more than two stations incurring a collision. next collision effectively by choosing a large backoff
The backoff counter is uniformly distributed and the counter, although such a large CW may result in more
parameter avg_paused_count for average number of idle timeslots during the backoff procedure. The idea
165
4. here is that the overheads of collided frames are
usually larger than waiting for idle timeslots. The Control rate 1 Mbits/s
parameter rd (where rd is a number for division) used in Data rate 11 Mbits/s
the pseudocode for the PCB algorithm below
Slot_time 20 μs
determines the size of the new CW. The new CW
computed using rd and CWmax addresses the fairness SIFS 10 μs
issue among stations in step 1 when a station does not DIFS 50 μs
calculate the system status correctly. The new CW CWmin 32
could reset the inappropriate CW and adjust CW again
CWmax 1024
after an observation period.
Packet size 1000 bytes
Pseudocode of PCB algorithm
Step 1 : estimation
• Goodput:
avg _ pause _ count = (1 − α ) * avg _ pause _ count + α * current _ pause _ count Goodput is the most common performance metric
that calculates total data amount received in a period
Step 2 : setting CW
by a station. In general, a higher goodput always
when collision occurs
set CW new = CW max / rd
indicates better efficiency in a system. In this paper,
we use aggregate goodput to evaluate PCB and
when transmissi on succeeds related backoff algorithms.
if during observatio n period
CW new = current CW
• Fairness Index:
else Fairness among stations is an important problem
CW new = avg _ pause _ count * β in BEB study and has been discussed by many
restart a new observatio n period
researchers. Fairness index could show if resource is
fairly allocated to each stations. Authors in [8]
4. Performance evaluation derived a fairness index using the formula given
below:
This section evaluates the system performance of
the proposed PCB algorithm with other existing
(∑ G )
i i
2
(3)
Fairness Index =
n * ∑ (G )
2
backoff algorithms under different system loads. The i i
simulation is performed using NS-2 version 2.28 Where n is the number of stations and Gi is the
simulator [7]. We use IEEE 802.11b based WLAN goodput of station i achieved. The value of the
setup and we assume transmissions without the fairness index is bounded to the interval [0, 1]. The
Request to Send/Clear to Send (RTS/CTS) mechanism index is equal to 1 when all stations obtain the same
in an ideal channel. Each mobile station establishes a goodput.
Constant Bit Rate (CBR) flow with a 2 Mbps link to • Collision Rate:
the base station. The number of stations is varied from Collision rate gives a probability that packets be
5 to 50 and the duration of simulation is set to 30 discarded due to collisions in each transmission. A
seconds. The parameters used in the simulation are higher collision rate usually indicates heavy system
listed in Table 1. The parameters ri and rd in EIED load and implies more overheads.
algorithm are set to 2 as suggested in [5]. For AEDCF, • Average end-to-end delay:
we set the observation period of the estimated collision End-to-End delay is the time it takes for a packet
rate to 0.5 seconds and α to 0.8 used in [6]. In the to travel from sender to receiver. For some time-
proposed PCB algorithm, we set the weight α to 0.9 to constraint applications, end-to-end delay is the most
obtain a smooth pause count. The parameter β is set to concern than other metrics. In this paper, we
5 which mean the expected collision rate Pc of a station calculate the average end-to-end delay in the system
is around 20% in heavy network load by PCB by various backoff algorithms.
algorithm. The parameter rd is set to 4 to get a large
size of new CW that is value 256 in IEEE 802.11b 4.1 Goodput Performance
after collisions.
We use the following performance metrics to Figure 3 shows the goodput performance results of
evaluate the performance of PCB with other previously various backoff algorithms for IEEE 802.11 WLANs.
proposed algorithms: The efficiency of standard DCF performs worse (as
Table 1 IEEE 802.11 b MAC and network parameters expected) when more stations contend for the channel.
used in simulation Although the EIED algorithm takes an exponential
166
5. decrease CW policy instead of resetting to CWmin when
there is a successful transmission, the curve decreases
when there are more active stations in the system. This
means that stations applying EIED and DCF
algorithms make decisions with unclear system status
and adjust the CW quickly from the result of a single
transmission. In contrast to EIED and DCF, the
goodput of AEDCF and PCB algorithms remains high
with respect to various system loads. These
improvements mean that stations using AEDCF and Figure 3. Aggregate goodput vs. number of stations
PCB algorithms adjust CW value appropriately
according to the load variation within the network. In
case of a light system load, when there is a collision,
PCB wastes some idle timeslots due to the large new
value of CW. The graph of PCB has maximum
goodput at around 20 stations. When the number of
stations increases, the overheads of collision decreases
the efficiency in PCB. Overall, the PCB algorithm
obtains a high efficiency compared with other backoff
algorithms in various network conditions. Although
Figure 3 shows that AEDCF performs consistently
better compared to PCB, we demonstrate further below Figure 4. Fairness index vs. number of stations
other additional performance (e.g.,fairness, collision
rate, average end-to-end delay) benefits provided by
PCB over AEDCF.
4.2 Fairness Index
The aggregate goodput in Figure 3 can represent
the efficiency of a system. However, when designing a
backoff algorithm, we should also consider another
important criterion: fairness among stations. The worst
case scenario is when one station sets a very small CW
due to inaccurate calculations of the system status and Figure 5. Collision rate vs. number of stations
as a result always occupies the channel. The aggregate
goodput is high but it is unfair to other stations. In simulation enlarges the goodput of stations achieved at
Figure 4, we present the fairness index of each backoff the end of the experiments.
algorithm among stations. Using the simulation setup
described in prior section, we executed the simulation 4.3 Collision Rate
for 30 iterations and we calculated a 95% confidence
interval. From Figure 4, the proposed PCB algorithm Figure 5 presents the collision rate of various
has the most stability and is close a fairness index of backoff algorithms. As expected, a high collision rate
one when compared with other contention algorithms. usually indicates additional overheads and longer end-
We also observe that the fairness index of AEDCF and to-end delays. From the simulation results, more frame
EIED are low and oscillatory. This phenomenon means collisions occurred as the number of active stations in
some stations occupy more channel capacity than other the system grows. The collision rate of a standard DCF
stations due to a different understanding of the system is the highest among the compared algorithms due to
status among stations. In the case of the AEDCF the resetting behavior for each successful transmission.
algorithm, the estimated collision rate dominates the In the case of n=50, the collision rate is around 50%.
new CW size. A slight difference in the estimated The PCB algorithm achieved a low collision rate when
collision rates among stations at the start of the compared with other backoff algorithms (as shown in
Figure 5). According to the parameter β setting, the
collision rate is around 20% as we expected in heavy
system load in Figure 5. A low collision rate indicates
that the station effectively reduces the retransmission
167
6. overheads in the system. However, a low collision rate
does not mean the least overhead in the system. Even a
large CW can result in a low collision rate. In the mean
time, the duration of idle channels causes the efficiency
of the system to decrease. Therefore, a good backoff
algorithm should also examine another metric such as
end-to-end delay.
Figure 7 Normalized delay vs. number of stations
4.4 End-to-End Delay 6. References
The variation of the mean end-to-end delay with [1] IEEE WG, “Part 11: Wireless LAN Medium Access
Control (MAC) and Physical Layer (PHY)
number of active stations is presented in Figure 6. As
Specifications,” IEEE 802.11 Standard, 1999.
expected, the delay increases with the number of [2] Andras Veres, Andrew T. Campbell, Michael Barry, and
stations. The objective of the PCB algorithm is that it Li_Hsiang Sun, “Supporting Service Differentiation in
precisely estimates the actual network status and sets Wireless Packet Networks Using Distributed Control,”
the corresponding CW to minimize overheads in the IEEE Journal on Selected Areas in Communications, vol.
system. In Figure 6, the PCB shows the advantage of 19, no. 10, October 2001.
overhead reduction and obtains the lowest delay [3] Chonggang Wang, Bo Li, and Lemin Li, “A New
among these backoff algorithms. In Figure 7, we Collision Resolution Mechanism to Enhance the
present the gain on end-to-end delay by normalizing Performance of IEEE 802.11 DCF," IEEE Transaction on
Vehicular Technology, vol. 53, no. 4, pp. 1235-1246,
end-to-end delay of a standard DCF. The delay of the
July 2004.
PCB is around 20% less than that of a standard DCF in [4] Bianchi G., “Performance analysis of the IEEE 802.11
the case of n = 50. However, the end-to-end delay is distributed coordination function,”IEEE Journal on
too large for multimedia services. The reason for the Selected Areas in Communications, vol. 18(3), pp. 535-
results is that 802.11b is throughput-oriented without 547, 2000.
considering QoS requirements. [5] N.-O. Song, B.-J. Kwak, J. Song, and L. E. Miller,
“Enhancement of IEEE 802.11 distributed coordination
5. Conclusion and Future Work function with exponential increase exponential decrease
backoff algorithm,” in Proc. IEEE VTC-Sprin, 2003, vol.
4, pp. 2775-2778.
In this paper, we have proposed a PCB backoff [6] Lamia Romdhani, Qiang Ni, and Thierry Turletti,
algorithm to improve the efficiency of IEEE 802.11 “Adaptive EDCF: Enhanced Service Differentiation for
DCF function. Our PCB algorithm estimates system IEEE 802.11 Wireless Ad-Hoc Networks”, in Proc. IEEE
status by using a pause count backoff counter and WCNC 2003, vol. 2, pp.1373-1378
determines a proper contention window size that [7] Network Simulator 2, http://www.isi.edu/nsnam/ns .
accurately matches current network conditions. We [8] R. Jain, D. Chiu, and W. Hawe, “A Quantitative Measure
compared the performance of PCB with past proposed of Fairness and Discrimination for Resource Allocation
in Shared Computer Systems,” DEC Research Report
algorithms such as IEEE 802.11 DCF, EIED, and
TR-301, 1984.
AEDCF. Our simulation results demonstrate that PCB
outperforms these previously proposed algorithms for
various performance metrics and dynamically adapts to
the variations in a network. In the future, we plan to
consider an extension of this work to consider
RTS/CTS mode and wireless transmission errors.
Figure 6 End-to-end delay vs. number of stations
168