Data Transformation In Between Nodes In Ieee Computer Science
Quality of Service (QoS) support in IEEE 802.11-based ad hoc networks relies on the networks' ability to estimate the available bandwidth on a given link. However, no mechanism has been standardized to accurately evaluate this resource. This remains one of the main issues open to research in this field. This paper proposes an available bandwidth estimation approach which achieves more accurate estimation when compared to existing research. . Our scheme does not modify the CSMA/CA MAC protocol in any manner, but gauges the effect of phenomena such as medium contention, channel interference, which influence the available bandwidth, on it. Based on the effect of the phenomena on the working of the medium-access scheme, we estimate the available bandwidth of a wireless host to each of its neighbors.The proposed approach differentiates the channel busy caused by transmitting or receiving from that caused by carrier sensing, and thus improves the accuracy of estimating the overlap probability of two adjacent nodes' idle time. Simulation results testify the improvement of this approach when compared with well known bandwidth estimation methods in the literature.Index Terms-Wireless sensor networks, IEEE 802.11, ad hoc networks, path discovery quality of service, available bandwidth estimation.1. Introduction
Ad hoc networks are autonomous, self-organized, wireless, and mobile networks. They do not require setting up any fixed infrastructure such as access points, as the nodes organize themselves automatically to transfer data packets and manage topology changes due to mobility. Many of the current contributions in the ad hoc networking community assume that the underlying wireless technology is the IEEE 802.11 standard due to the broad availability of interface cards and simulation models. This standard provides an ad hoc mode, allowing mobiles to communicate directly. As the communication range is limited by regulations, a distributed routing protocol is required to allow long distance communications. However, this standard has not been targeted especially for multihop ad hoc operation, and it is therefore not perfectly suited to this type of networks. Nowadays, several applications generate multimedia data flows or rely on the proper and efficient transmission of sensitive control traffic. These applications may benefit from a quality of service (QoS) support in the network. That is why this domain has been extensively studied and more and more QoS solutions are proposed for ad hoc networks. However, the term QoS is vague and gathers several concepts. Some protocols intend to offer strong guarantees to the applications on the transmission characteristics, for instance bandwidth, delay, packet loss, or network load. Other solutions, which seem more suited to a mobile environment, only select the best route among all possible choices regarding the same criteria. In both cases, an accurate evaluation of the capabilities of the routes is necessary. Most of the current QoS proposals leave this problem aside, relying on the assumption that the link layer protocols are able to perform such an evaluation. However, they are not. The resource evaluation problem is far from being trivial as it must take into account several phenomena related to the wireless environment but also dependent on less measurable parameters such as the node mobility.
The IEEE 802.11-based networks have been able to provide a certain level of quality of service (QoS) by the means of service differentiation, due to the IEEE 802.11e amendment. Such an evaluation would, however, be a good asset for bandwidth-constrained applications. In multihop ad hoc networks, such evaluation becomes even more difficult. Consequently, despite the various contributions around this research topic, the estimation of the available bandwidth still represents one of the main issues in this field.2 RELATED WORK2.1 Wireless sensor network
A wireless sensor network (WSN) is a wireless network consisting of spatially distributed autonomous devices using sensors to cooperatively monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants, at different locations. The development of wireless sensor networks was originally motivated by military applications such as battlefield surveillance. However, wireless sensor networks are now used in many civilian application areas, including environment and habitat monitoring, healthcare applications, home automation, and traffic control. In addition to one or more sensors, each node in a sensor network is typically equipped with a radio transceiver or other wireless communications device, a small microcontroller, and an energy source, usually a battery. The envisaged size of a single sensor node can vary from shoebox-sized nodes down to devices the size of grain of dust, although functioning 'motes' of genuine microscopic dimensions have yet to be created. The cost of sensor nodes is similarly variable, ranging from hundreds of dollars to a few cents, depending on the size of the sensor network and the complexity required of individual sensor nodes.[ Size and cost constraints on sensor nodes result in corresponding constraints on resources such as energy, memory, computational speed and bandwidth.2.2 Wireless network
Wireless network refers to any type of computer network that is wireless, and is commonly associated with a telecommunications network whose interconnections between nodes is implemented without the use of wires. Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses electromagnetic waves, such as radio waves, for the carrier and this implementation usually takes place at the physical level or "layer" of the network Wireless networks have had a significant impact on the world as far back as World War II. Through the use of wireless networks, information could be sent overseas or behind enemy lines easily, efficiently and more reliably. Since then, wireless networks have continued to develop and their uses have grown significantly. Cellular phones are part of huge wireless network systems. People use these phones daily to communicate with one another. Sending information overseas is possible through wireless network systems using satellites and other signals to communicate across the world. Another important use for wireless networks is as an inexpensive and rapid way to be connected to the Internet in countries and regions where the telecom infrastructure is poor or there is a lack of resources, as in most developing countries.
Compatibility issues also arise when dealing with wireless networks. Different components not made by the same company may not work together, or might require extra work to fix these issues. Wireless networks are typically slower than those that are directly connected through an Ethernet cable.
A wireless network is more vulnerable, because anyone can try to break into a network broadcasting a signal. Many networks offer WEP - Wired Equivalent Privacy Another type of security for wireless networks is WPA - Wi-Fi Protected Access. WPA provides more security to wireless networks than a WEP security set up.2.3 Routing
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network, electronic data networks (such as the Internet), and transportation (transport) networks. This article is concerned primarily with routing in electronic data networks using packet switching technology.
In packet switching networks, routing directs forwarding, the transit of logically addressed packets from their source toward their ultimate destination through intermediate nodes; typically hardware devices called routers, bridges, gateways, firewalls, or switches. The routing process usually directs forwarding on the basis of routing tables which maintain a record of the routes to various network destinations. Thus constructing routing tables, which are held in the routers' memory, becomes very important for efficient routing. Most routing algorithms use only one network path at a time, but multipath routing techniques enable the use of multiple alternative paths.
Routing, in a more narrow sense of the term, is often contrasted with bridging in its assumption that network addresses are structured and that similar addresses imply proximity within the network. Because structured addresses allow a single routing table entry to represent the route to a group of devices, structured addressing (routing, in the narrow sense) outperforms unstructured addressing (bridging) in large networks.2.4 Network congestion
In data networking and queuing theory, network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates. Typical effects include queuing delay, packet loss or the blocking of new connections. A consequence of these latter two is that incremental increases in offered load lead either only to small increase in network throughput, or to an actual reduction in network throughput.
Thus, networks using these protocols can exhibit two stable states under the same level of load. The stable state with low throughput is known as congestive collapse.2.5 Congestive collapse
Congestive collapse (or congestion collapse) is a condition which a packet switched computer network can reach, when little or no useful communication is happening due to congestion.
When a network is in such a condition, it has settled (under overload) into a stable state where traffic demand is high but little useful throughput is available, and there are high levels of packet delay and loss2.6 Ad hoc On-Demand Distance Vector (AODV)
Ad hoc On-Demand Distance Vector (AODV) Routing is a routing protocol for mobile ad hoc networks (MANETs) and other wireless ad-hoc networks. It is jointly developed in Nokia Research Center of University of California, Santa Barbara and University of Cincinnati by C. Perkins and S. Das. AODV is capable of both unicast and multicast routing. It is a reactive routing protocol, meaning that it establishes a route to a destination only on demand. In contrast, the most common routing protocols of the Internet are proactive, meaning they find routing paths independently of the usage of the paths. AODV is, as Other AODV nodes forward this message, and record the node that they heard it from, creating an explosion of temporary routes back to the needy node. When a node receives such a message and already has a route to the desired node, it sends a message backwards through a temporary route to the requesting node. The needy node then begins using the route that has the least number of hops through other nodes. Unused entries in the routing tables are recycled after a time. When a link fails, a routing error is passed back to a transmitting node, and the process repeats. Nodes use this sequence number so that they do not repeat route requests that they have already passed on. Another such feature is that the route requests have a "time to live" number that limits how many times they can be retransmitted. Another such feature is that if a route request fails, another route request may not be sent until twice as much time has passed as the timeout of the previous route request.
The advantage of AODV is that it creates no extra traffic for communication along existing links. Also, distance vector routing is simple, and doesn't require much memory or calculation. However AODV requires more time to establish a connection, and the initial communication to establish a route is heavier than some other approaches. The Ad hoc On-Demand Distance Vector (AODV) Routing protocol uses an on-demand approach for finding routes, that is, a route is established only when it is required by a source node for transmitting data packets. However, in AODV, the source node and the intermediate nodes store the next-hop information corresponding to each flow for data packet transmission.
In an on-demand routing protocol, the source node floods the Route Request packet in the network when a route is not available for the desired destination. It may obtain multiple routes to different destinations from a single Route Request. The major difference between AODV and other on-demand routing protocols is that it uses a destination sequence number (DestSeqNum) to determine an up-to-date path to the destination. A node updates its path information only if the DestSeqNum of the current packet received is greater than the last DestSeqNum stored at the node. A RouteRequest carries the source identifier (SrcID), the destination identifier (DestID), the source sequence number (SrcSeqNum), the destination sequence number (DesSeqNum), the broadcast identifier (BcastID), and the time to live (TTL) field. DestSeqNum indicated the freshness of the route that is accepted by the source. When an intermediate node receives a RouteRequest, it either forwards it or prepares a RouteReply if it has a valid route to the destination. The validity of a route at the intermediate node is determined by comparing the sequence number at the intermediate node with the destination sequence number in the Route Request packet. If a Route Request is received multiple times, which is indicated by the BcastID-SrcID pair, the duplicate copies are discarded. All intermediate nodes having valid routes to the destination, or the destination node itself, are allowed to send RouteReply packets to the source. Every intermediate node, while forwarding a RouteRequest, enters the previous node address and its BcastID. A timer is used to delete this entry in case a RouteReply is not received before the timer expires. This helps in storing an active path at the intermediate node as AODV does not employ source routing of data packets. When a node receives a RouteReply packet, information about the previous node from which the packet was received is also stored in order to forward the data packet to this next node as the next hop toward the destination.3. SYSTEM DESIGN AND IMPLEMENTATION3.1 System design:
In this system using 802.11 MAC layer to evaluate the correct bandwidth.This method combines channel monitoring to estimate each node's medium occupancy. Probabilistic combination of the values is to account for synchronization between nodes, estimation of the collision probability between each couple of nodes, and variable overhead's impact estimation. This mechanism only requires one-hop information communication and may be applied without generating a too high additional overhead.We show the accuracy of the available bandwidth measurement through NS-2 simulations. These results show that single-hop flows and multihop flows are admitted more accurately, resulting in a better stability and overall performance.3.2 Existing System:
The ad hoc networking community assumes that the underlying wireless technology is the IEEE 802.11 standard due to the broad availability of interface cards and simulation models. This standard has not been targeted especially for multihop ad hoc operation, and it is therefore not perfectly suited to this type. An accurate evaluation of the capabilities of the routes is necessary. Most of the current QoS proposals leave this problem aside, relying on the assumption that the link layer protocols are able to perform such an evaluation.3.3 Proposed System:
In this system they are using 802.11 MAC layer to evaluate the correct bandwidth. This method combines channel monitoring to estimate each node's medium occupancy. Probabilistic combination of the values is to account for synchronization between nodes, estimation of the collision probability between each couple of
nodes, and variable overhead's impact estimation. This mechanism only requires one-hop information communication and may be applied without generating a too high additional overhead. We show the accuracy of the available bandwidth measurement through NS-2 simulations. These results show that single-hop flows and multihop flows are admitted more accurately, resulting in a better stability and overall performance.3.3.1 Packet Creation:
In this module we split the Data in to N number of fixed size packet with Maximum length of 48 Characters.3.3.2Apply the RREQ and get RREP:
The aim of the RREQ is to find a route between the sender and the receiver that meets the constraints specified by the application level in terms of Bandwidth. Therefore, two flows with the same source and destination can follow different routes depending on the network state.
When a source node has data to send, it broadcasts a route request (RREQ) to its neighbours. The RREQ packet contains the address of the sender, and the requirements at the application level, the destination address, and a sequence number. The Intermediate Node or Destination Node sends RREP if it is free, otherwise, it silently discards the message.
When a source node has data to send, it broadcasts a route request (RREQ) to its neighbors. The RREQ packet contains the address of the sender, the channel use, the requirements at the application level, the destination address, and a sequence number. Each mobile node that receives such an RREQ performs an admission control by simply comparing the bandwidth requirement carried in the RREQ packet to the estimated available bandwidth on the link it received the RREQ on. If this check is positive, the node adds its own address to the route and forwards the RREQ; otherwise, it silently discards the message. This step is different from the other tested protocols as the admission control is done at the receiver side and not at the sender side. This is explained by the fact that, in ABE, each node stores the available bandwidths of its ingoing links. Finally, if the destination receives a first RREQ, it sends a unicast route reply (RREP) to the initiator of the request along the reverse path. The resources are then reserved and the new QoS flow can be sent.3.3.3Admission Control Mechanism
The Admission Control Mechanism is done in the receiver side. The Admission Control Mechanism has the all status of the node so if the nodes want to send RREP or discard the message, the particular node check the status by using the Admission Control Mechanism.126.96.36.199 Integration into AODV: Admission Control
We have slightly modified AODV in order to transform it into a QoS protocol based on ABE. It thus becomes a cross-layer routing protocol. The MAC layer estimates proactively and periodically the available bandwidth of the neighboring links, and the routing layer is in charge of discovering QoS routes complying to the application demands, basing its decisions on the MAC layer information.188.8.131.52 Route Discovery
The aim of the route discovery procedure is to find a route between the sender and the receiver that meets the constraints specified by the application level in terms of bandwidth. Therefore, two flows with the same source and destination can follow different routes depending on the network state. When a source node has data to send, it broadcasts a route request (RREQ) to its neighbors. The RREQ packet contains the address of the sender, the channel use, and the requirements at the applications level, the destination address, and a sequence number. Each mobile node that receives such an RREQ performs an admission control by simply comparing the bandwidth requirement carried in the RREQ packet to the estimated available bandwidth on the link it received the RREQ on. If this check is positive, the node adds its own address to the route and forwards the RREQ; otherwise, it silently discards the message. This step is different from the other tested protocols as the admission control is done at the receiver side and not at the sender side. This is explained by the fact that, in ABE, each node stores the available bandwidths of its ingoing links. Finally, if the destination receives a first RREQ, it sends a unicast route reply (RREP) to the initiator of the request along the reverse path. The resources are then reserved and the new QoS flow can be sent.184.108.40.206 Intraflow Contention Problem
Simply comparing the bandwidth application requirement and a link available bandwidth is not sufficient to decide about the network ability to convey a flow. Indeed, the intraflow contention problem has to be considered when performing multihop admission control. In , the authors compute a value called contention count (CC) of a node along a given path. This value is equal to the number of nodes on the multihop path that are located within the carrier sensing range of the considered node. To calculate the CC of each node, the authors analyze the distribution of the signal power. As in , for simplicity reasons, in ABE, we rather use a direct relationship between the end-to-end throughput and the number of hops. Hence, after consideration of the intraflow contention on an intermediate node j, which is located at H hops from the source and has received the RREQ from a node i, the available bandwidth considered for admission control, denoted by B (i,j) is equal to
Where Efinal (b (i, j)) is the available bandwidth of link (I, j) as computed by ABE.3.3.4 Bandwidth Utilized
After the source nodes send the total message to the Destination Node finally we calculate the end to end delivery of the Bandwidth and Time delay.
Whenever a node needs to send a frame, it first needs to contend for medium access and it cannot emit its frame unless the medium is free. Therefore, a potential sender needs to evaluate the load of the medium, i.e., the proportion of time the medium is idle to determine the chance it has to successfully gain access to the shared resource. Such evaluation is also performed by the solutions proposed. Let us consider a node s in the network during an observation interval of Î” seconds.
We use the following notations:
Tidle(s) is the total idle time, i.e., the total time during which node s neither emits any frame nor senses the medium busy. Both physical and virtual carrier sense mechanisms should report an idle state. This includes periods during which no frame is ready to be emitted as well as periods of deferral (backoff time and interframe spacing). Bs is the bandwidth available to node s, i.e., the maximum throughput it can emit without degrading close flow's rate. Cmax is the capacity of the medium.
During an arbitrary observation interval Î”, each node may monitor the radio medium in its surroundings and measure the total amount of time Tidle that is idle for emitting frames. To adapt the evaluation to the MAC protocol's behavior, periods of time shorter than IEEE 802.11's DIFS timing shall not be added to the total idle time count, as such intervals do not allow any backoff decrease nor medium access.
As the medium is considered busy as soon as a signal above the carrier sensing threshold is received, this method does not only take into account the bandwidth used in the transmission range of the nodes but also in the whole carrier sensing area.
Fig. 3. Medium idle periods of sender and receiver that never overlap.
As this monitoring neither takes into account the IEEE 802.11's variable overhead nor is the reception side of the transmission, the available bandwidth computed by this method at node s imprecise. However, it provides a threshold above which the medium access probability decreases rapidly. Some frames may still be successfully emitted, though, due to a favorable scheduling of transmissions or to capture effects. As long as the medium load remains below this threshold, a scheduling between different contending emitters preventing two simultaneous emissions exists.
We therefore consider that this value is an upper bound of the available bandwidth we are seeking:
Bs â‰¤ (Tidle(s)/Î”). Cmax
The reader should note that the value of Cmax shall not represent the raw medium capacity, as advertised by the standard, but must take into account the fixed overhead (headers, acknowledgments. . .) introduced by the MAC protocol. For example, a 54-Mbps implementation of IEEE 802.11 cannot deliver throughputs higher than 33.2 Mbps.220.127.116.11 Available Bandwidth Estimation
For ensuring delay guarantees, our solution relies on an accurate available bandwidth estimation. Hereafter, we define the available bandwidth between two neighbor nodes as the maximum throughput that can be transmitted between these two peers without disrupting any ongoing flow in the network. This term should not be confused with the link capacity (also called base bandwidth) that designates the maximum throughput a flow can achieve between two neighbor nodes, even at the cost of other flows' level of service degradation. For the available bandwidth estimation, we choose the protocol ABE (Available Bandwidth Estimation), first proposed in  and then refined in . In , the authors show that ABE is more accurate than many protocols with the same goal while requiring a small overhead. By considering the overlapping of the silence periods of both emitter and receiver of a link, the collision probability that exists on the link and the backoff window size correlated to this collision probability, ABE provides an accuracy in the estimation that is often not achieved by the other protocols.
As our delay estimation depends strongly on this available bandwidth estimation, this section is devoted to the description of ABE. Of course, we can not include all the details of ABE that is not the novelty of our proposition. The interested reader can refer to [9, 10]. For providing an accurate evaluation, some phenomena need to be taken into account when the IEEE 802.11 MAC protocol operates:
â€¢ Carrier sense mechanism prevents two close emitters from transmitting simultaneously. Therefore, an emitter shares the channel bandwidth with all these close emitters. The channel utilization has to be monitored to evaluate the capacity of a node to emit a given traffic volume. As in many protocols, this channel utilization is computed by each node by monitoring the radio medium in its surroundings and measuring the total amount of time that is idle for emitting frames. Therefore, this method does not only take into account the bandwidth used in the transmission range of the nodes but also in the whole carrier sensing area.
â€¢ For a transmission to take place, both emitter and receiver need that no jamming occurs during the whole transmission. Therefore, the value of the available bandwidth on a link depends on both peers' respective channel utilization ratios but also on the idle periods synchronization. In , we propose a probabilistic method to estimate this synchronization. This estimation, for the link (s, r), is denoted E(b(s,r)) in the following.
â€¢ No collision detection is possible in a wireless environment. Therefore, whenever collisions happen, both colliding frames are completely emitted, maximizing the bandwidth loss. It is thus necessary to integrate this bandwidth loss in the available bandwidth estimation. In , we provide an estimation of the collision probability on each link. This estimation combines two approaches:
i) A on line approach that computes the impact of the medium occupancy distribution at the receiver side thanks to the collision probability on Hello packets. These Hello packets are used in many ad hoc routing protocols and are required for computing the previous estimation E(b) on each link;
ii) A off line approach that takes into account the size of the packets sent by the source thanks to an interpolation. The goal of this last approach is to compute the collision probability that packets of known and fixed size will undergo on a link from the collision probability of Hello packets deduced from real measurements on the same link. This collision probability estimation is denoted p, in the following, and depends on the size of packets that will be sent.
â€¢ Finally, when collisions happen on unicast frames, the IEEE 802.11 protocol automatically retries to emit the same frame, drawing the backoff counter in a double-sized contention window. The time lost in additional overhead may also have an impact on the available bandwidth. In , we compute the mean backoff according to p the collision probability computed in the previous estimation. It is then possible to deduce the proportion of bandwidth consumed by the backoff mechanism. This proportion is denoted by K in the following. These different estimations are then combined to estimate the available bandwidth on a wireless link, i.e. between an emitter s and a receiver r:
Efinal (b(s, r))= (1 âˆ’ K) Â· (1 âˆ’ p) Â· E (b(s,r))
This procedure has implemented in every node in the network while the path establishment continues by the AODV protocol as an interface among the nodes.
Fig. 8. Available bandwidth for the link synchronization scenario, considering collisions' impact.
The source node selects the destination node first and then by using the browse button we select some text file and this text file is send to the destination side.4 CONCLUSIONS AND FUTURE WORKS
In this paper, we have presented a new technique to compute the available bandwidth between two neighbor nodes and by extension along a path. This method combines channel monitoring to estimate each node's medium occupancy including distant emissions, probabilistic combination of these values to account for synchronization between nodes, estimation of the collision probability between each couple of nodes, and variable overhead's impact estimation. This mechanism only requires one-hop information communication and may be applied without generating a too high additional overhead. This technique has been integrated in AODV for comparison purposes. We show the accuracy of the available bandwidth measurement through NS-2 simulations. These results show that single-hop flows and multihop flows are admitted more accurately, resulting in a better stability and overall performance. Results are encouraging in fixed networks as well as in mobile networks. From our point of view, these scenarios prove that the most
Fig. 12. Throughput obtained by AODV, AAC, BRuIT, and ABE-AODV in mobile networks. (a) AODV. (b) AAC. (c) ABE-AODV. (d) BRuIT..
As future works, we plan to focus on two issues. First, in our current evaluation, we make no difference between the bandwidth consumed by QoS flows and the bandwidth consumed by best effort flows. Therefore, it may be possible that a node considers its available bandwidth on a link as almost null whereas the whole bandwidth is consumed by best effort flows. Decreasing the rate of these flows may lead to a higher acceptance rate of QoS flows. Differentiating flow types may also result in a better utilization of the network resources. In parallel, we are investigating the delay metric, as preliminary studies indicate that some parts of the approach described in this paper may be used or converted to this other important parameter.
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