Network Is Self Configuring Infrastructureless Computer Science Essay

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A mobile ad-hoc network is a self-configuring infrastructureless network of mobile devices associated by wireless link. In MANET the demanding factor is to implement an efficient multipath multicast transmission technique.In this study two routing protocol AOMDV and EGMP for multipath multicast transmission has been developed. From this study it is observed that multipath multicast transmission is efficient in MANET network. Our simulation results demonstrates that EGMP has high packet delivery ratio, low control overhead and low outage probability. In future security relate issues in MANET can also be dealt.

INTRODUCTION

As the importance of computers in our daily life increases it also sets new demands for connectivity. Wired solutions have been around for a long time but there is increasing demand on working wireless solutions for connecting to the Internet, reading and sending E-mail messages, changing information in a meeting and so on. There are solutions to these needs, one being wireless local area network that is based on IEEE 802.11 standard. However, there is increasing need for connectivity in situations where there is no base station available. This is where ad hoc networks step in.

The strength of the connection can change rapidly in time or even disappear completely. Nodes can appear, disappear and re-appear as the time goes on and all the time the network connections should work between the nodes that are part of it. As one can easily imagine, the situation in ad hoc networks with respect to ensuring connectivity and robustness is much more demanding than in the wired case.

Ad hoc networks are networks are not (necessarily) connected to any static (i.e. wired) infrastructure. An ad-hoc network is a LAN or other small network, especially one with wireless connections, in which some of the network devices are part of the network only for the duration of a communications session or, in the case of mobile or portable devices, while in some close proximity to the rest of the network. The ad hoc network is a communication network without a pre-exist network infrastructure.

The MANET network has the following characteristics such as communication via wireless mean, nodes can perform the roles of both hosts and routers, no centralized controller and infrastructure, dynamic network topology, energy constraint and limited security.

In on-demand or reactive routing protocols, the routes are created on requirement basis. To find a path from source to destination, it invokes the route discovery mechanisms. Only the routes that are currently in use are maintained a. Reactive routing protocols have some inherent limitations. First, since routes are only maintained while in use, it is usually required to perform a route discovery before packets can be exchanged between communication peers. This leads to a delay for the first packet to be transmitted. Second, even though route maintenance for reactive algorithms is restricted to the routes currently in use, it may still generate an important amount of network traffic when the topology of the network changes frequently. Finally, packets to the destination are likely to be lost if the route to the destination changes [1]. To reduce the topology maintenance over-head in multicasting, an option is to make use of the position information. But there are many challenges to implement an efficient and scalable geographic multicast scheme in MANET. For example, in unicast geographic routing, destination's position is carried in the packet header to guide packet forwarding. But in multicast routing, the destination is a group of members. Putting all the members' addresses and positions into the packet header is a direct and easy way, but this is only applicable for the small group case [2] [3] [4]. Besides scalable packet forwarding, a scalable geographic multicast protocol also needs to efficiently manage the membership of a possible large group, obtain the members' positions and forward packets to the members distributed in a possible large network terrain. These are ignored in the above protocols. We propose an efficient geographic multicast protocol (EGMP). EGMP can scale to large group size and network size and can efficiently implement multicasting delivery.

The MANET find its application in the following fields military, disaster relief operation , mine site operation and robot data acquisition.

ROUTING PROTOCOL AND TRANSMISSION MECHANISM

A routing protocol is a protocol that specifies the way in which routers communicate with each other, disseminating information that enables them to select routers between any two nodes or a computer network, the choice of route being done by routing algorithm. Each router has a prior knowledge of network attached directly to it. A routing protocol shares information first among immediate and then throughout the network.

Ad-hoc On-demand Multipath Distance Vector Routing (AOMDV)

Before describing AOMDV, we first discuss AODV, from which it is derived. In AODV, when a source needs a route to a destination, it initiates a route discovery process by flooding a RREQ for destination throughout the network. RREQs should be uniquely identified by a sequence number so that duplicates can be recognized and discarded. Upon receiving a non-duplicate RREQ, an intermediate node records previous hop and checks whether there is a valid and fresh route entry to the destination in routing table. If such is the case, the node sends back a RREP to the source; if not it rebroadcasts the RREQ. A node updates its routing information and propagates upon receiving further RREPs only if a RREP contains either a larger destination sequence number (fresher) or a shorter route found. AOMDV has numerous features. AOMDV discovers routes on demand using route discovery method. The most important variation is the amount of routes found in each route discovery. In AOMDV, RREQ transmission from source to the target establishes multiple reverse paths both at intermediate node in addition to the destination. Multiple reverse paths at intermediate nodes in addition to the destination. Multiple RREP's navigate this reverse route back to form multiple routes to target at the source and intermediate nodes.

The AOMDV uses the basic AODV route construction process. In this case, however, some extensions are made to create multiple loop-free, link-disjoint paths.The main idea in AOMDV is to compute multiple paths during route discovery. It consists of two components: 1) A route update rule to establish and maintain multiple loop-free paths at each node. 2) A distributed protocol to find link-disjoint paths.

In AOMDV this is used at the intermediate nodes. Duplicate copies of a RREQ are not immediately discarded. Each packet is examined to see if it provides a node-disjoint path to the source. For node-disjoint paths all RREQs need to arrive via different neighbors of the source. This is verified with the first hop field in the RREQ packet and the first hop list for the RREQ packets at the node. At the destination a slightly different approach is used, the paths determined there are link-disjoint, not node-disjoint. In order to do this, the destination replies up to k copies of the RREQ, regardless of the first hops.

Algorithm

Step1: Send request from source to the selected destinations.

Step2: Shortest multipath selection is done and transmission takes place.

Step3: Destination will send reply consisting hop count of route.

Step4: Multipath route selection is done and is updated in the routing table.

Step5: Divide the traffic on available routes as less hop count routes will assign more traffic.

Step6: Now transmit data according to the above division ratio through discovered routes.

Multipath Schemes

Routing is responsible to establish and maintain possible end-to-end paths from source to destination. The main challenge in video streams is to classify the routes that ensure the video delivery with a satisfying quality. In general, Multipath routing can improve QoS by providing the following:

Accumulation of bandwidth and delay: breaking the capacity of more than one route.

Route load balancing: balance the traffic load in higher number of nodes.

Fault tolerance: by adding redundancy, to reduce the effect of network failures onto affected video quality, it is important that the paths are disjoint. In case the Multipath routing protocol offers multiple paths with sufficient path diversity, it is less probable that a link failure affecting one of the paths simultaneously affects one of the other paths. This is especially beneficial in real-time streaming, where information is useful in checking the disjointness of alternate paths.

(a)

(b)

(a) AODV Routing table, (b) AOMDV Routing table

including: next hop, last hop, hop count, and expiration timeout.

AOMDV relies as much as possible on the routing information already available in the underlying AODV protocol, thereby limiting the overhead incurred in discovering multiple paths.

Figure shows the difference in the routing table entry structure between AODV and AOMDV. AOMDV route table entry has a new field for the advertised hop count. Besides a route list is used in AOMDV to store additional information for each alternate path.

Efficient Geographic Multicast Protocol

EGMP uses a two-tier structure. The whole network is divided into square zones. In each zone, a leader is elected and serves as a representative of its local zone on

the upper tier. The leader collects the local zone's group membership information and represents its associated zone to join or leave the multicast sessions as required.

As a result, a network-range core-zone-based multicast tree is built on the upper tier to connect the member zones. The source sends the multicast packets directly onto the tree. And then the multicast packets will flow along the multicast tree at the upper tier. When an on-tree zone leader receives the packets, it will send the multicast packets to the group members in its local zone.

The zone-based tree is shared for all the multicast sources of a group. To further reduce the packet forwarding overhead and delay, EGMP supports bi-directional packet forwarding along the tree structure. That is, instead of sending the packets to the root of the tree first, a source forwards the multicast packets directly along the tree. At the upper layer, the multicast packets will flow along the multicast tree both upstream to the root zone and downstream to the leaf zones of the tree. At the lower layer, when an on-tree zone leader receives the packets, it will send them to the group members in its local zone.

ALGORITHM

Step 1: Network is divided into square zone and in each zone a leader is elected. Zone leader (zLdr) maintains a multicast table.

Step 2: When a zone leader receives the NEW SESSION message, it will record the group ID and the root-zone ID in its multicast table.

Step 3: The leader will send JOIN REQ message towards root zone, on receiving it destination will sent back JOIN REPLY message back to source.

Step 4: The leader will send a JOIN REQ message to the zone to refresh cluster information.

Step 5: Multipath selection is done in the cluster using Dijikstras algorithm.

Step 6: Video is split and transmitted in the selected multipath to multiple selected destinations.

Step 7: When a zone leader receives END SESSION message, the node will remove all the information and stops the transmission.

Video Streaming Traffic

A video streaming flow can be split into multiple sub-streams and delivered through different network simultaneously. Based on video transmitted, each video traffic burst is generated over fixed intervals and consist of an I or P frame and number of B frame.

To remove temporal redundancy, intra-coded (I) frame are interleaved with predicted (P) frames and bi-directionally code (B) frames. I frames are compressed versions of raw frames independent of other frames, whereas P frames only refer preceding I/P frames and B frames can refer both preceding and succeeding frames. A sequence of video frames from I frame to next I frame comprises group of picture (GoP). Because P and B frames are encoded with reference to preceding and/or succeeding I/P frames, traffic transmission follows the batch arrival.

PROPOSED WORK

MULTIPATH ROUTING

Multipath routing [6] is the routing technique of leveraging multiple alternative paths through a network, which can yield a variety of benefits such as fault tolerance, increased bandwidth, improved delay, increased throughput or improved security. The ability of creating multiple routes from a source to a destination is used to provide a backup route. When the primary route fails to deliver the packets in some way, the backup is used.

MULTICAST ROUTING

Multicast communication [17] is an efficient solution for group applications in the Internet. Multicast conserves the network bandwidth by constructing a spanning tree between sources and receivers. A single copy of the data is sent to all the receivers through the multicast tree. Applications such as videoconferencing, distant learning or network games use video, audio and data traffic.

MULTIPATH MULTICASTING

Multipath Multicasting is based on three aspects:

1. Multipath selection and establishment

2. Multipath route maintenance

3. Load distribution for distributing traffic among multiple paths

Multipath Selection and Establishment

In AODV, when a node broadcasts a RREQ message, it is often likely to receive more than one response message since any node in the multicast tree can respond to the message. If the source node receives one or more RREP messages in this time, it queries the multicast table and check if the route is activated to confirm which one is the first arrival.

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Figure : Basic ad hoc architecture

The source node unicasts a MACT (Multicast Activation) to the node which RREP is the first arrival for activating the route and sends packets through the path due to the first path has the shortest latency. The intermediate nodes, which received MACT, activate the related entry in multicast table, and then forward the MACT to next hop until one group member receives MACT. Multiple paths are selected to reduce resource consumption and improve calculation efficiency.

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Figure : Multipath Multicasting

Multipath Route Maintenance

The wireless link is easy to break because of nodes mobility or other reasons. When a node doesn't receive any message from the adjacent node or can't send any packet to the next hop, it thinks the link is broken. When the intermediate nodes in this path receive RERR, they delete the entry in the route table, and continue to forwarding RERR until the source node receives RERR message. When the source node receives the RERR, it deletes the related entry in the route table, searches backup route table [6] and checks whether both paths are invalid. If the two paths are broken at the same time, the source node broadcasts RREQ to initiate a new route discovery.

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Figure : Link Failure

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Figure 4.4: Choosing an alternate path

Load Distribution

Once the path has been established, the source node starts to send packets [4] through multiple paths. It sends all packets through these paths in order to reduce latency caused by route discovery. This method can balance the network load and relieve the network congestion.

RESULTS AND DISCUSSIONS

SIMULATION SCENARIO

To evaluate the performance of the Modified-AOMDV routing protocol, NS2 is used. The Monarch research group in CMU has extended the NS-2 network simulator to include physical layer, link layer and MAC layer models to support multi-hop wireless network simulations.

In order to evaluate the performance of the multipath video multicasting and to compare it with conventional multicasting, the below parameters are configured in the network simulator.

No. of Nodes : 100

Protocol Used : AOMDV, EGMP

Dimension : 1000*1000

Channel Type : Wireless channel IEEE 802.11

Queue Type : Queue/DropTail/PriQueue

Antenna : Omni Antenna

Propagation Model : Two Ray Ground

PERFORMANCE EVALUATION

Performance Metrics

Packet Delivery Ratio

The ratio of the number of delivered data packet to the destination. This illustrates the level of delivered data to the destination. The greater value of packet delivery ratio means the better performance of the protocol.

∑ Number of packet receive / ∑ Number of packet send

Control Overhead

Control overhead is obtained on number of control route request packet and number of route reply packet. Total control packet sent also included in overhead calculation. Overhead does not increase with number of routes being created.

Outage Probability

Each interfering signal is subject to multipath and shadow fading and it is necessary to incorporate these effects in assessing the performance of wireless systems. In such an environment, the link performance evaluation depends on many channel parameters. To assess the impact of these different parameters evaluation metric called outage probability is evaluated. The outage probability is an important performance measure of communication links operating over composite fading/shadowing channels. It is defined as the probability that the output SIR falls below a given threshold.Outage probability is analyzed with respect to signal to interference ratio

Packet Delivery Ratio.

Figure : Comparison of AOMDV and EGMP on basis of Packet delivery ratio

Figure illustrates that the level of delivered information to the destination using EGMP algorithm is 2% higher than the AOMDV. Hence, Packet loss is reduced in EGMP

Control Overhead

Figure : Comparison of AODV and AOMDV on basis of control overhead

Figure shows the EGMP performs better than the AOMDV for different time intervals. Overhead is calculated and compared between EGMP and AOMDV algorithm. Comparison result shows the overhead decreases by 0.15% for EGMP algorithm than AOMDV algorithm. This indicates number of control packet in transmission is reduced.

Outage Probability

Figure : Comparison of AODV and AOMDV on basis of outage probability

Figure indicates the output Signal to Interference Ratio falls below a given threshold. As the normalized distance increases, the signal is prone to losses and outage probability reduces. It is observed that the outage probability has been decreased by 0.12% than the AOMDV.

CONCLUSION

In this project, the problem of real-time video multipath multicast communication over wireless adhoc networks has been analyzed. EGMP for multipath video multicast provides robustness for video applications. Simulation results show that the throughput of the multiple path multicast video using EGMP is significantly 20% higher than that of AOMDV video communication, with similar routing overhead and forwarding efficiency.

The simulated results proves by adopting EGMP protocol the QoS parameters, viz Throughput, Packet delivery ratio, Flow blocking has been significantly improved. Throughput has been increased by 20% for EGMP than AOMDV. It is also found that packet delivery ratio increased by 2% for EGMP and flow blocking is reduced by 2% for EGMP. Wireless multicast is required for a range of emerging wireless applications employing group communication among mobile users. Scope of the project is to transmit the video in real time applications using an emulator tool.

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