Analysis Of An Existing System Computer Science Essay

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In the Existing system we use the concept of reverse path forwarding. The per source tree scheme consists of broadcasting the packet from the source to all destinations along the source. Packet is received along the shortest path. This provision is required in order to avoid endless looping. The rooted shortest tree at each source generally comes for free since it is embedded in the routing tables of the most common routing algorithms such as Distance Vector and Link State.

Source tree multicast distributes the traffic evenly in the network it requires minimal initialization and maintenance, and it does not rely on a central control point. The per source tree approach presents a problem. Suppose a source moves faster than the routing tables can track it. Some of the nodes have obsolete routing tables which point in the "wrong direction".

Another popular wired network scheme is shared-tree multicast. In this scheme, a single tree rooted at a Rendezvous Point (RP) is maintained instead of many per source trees. The shared tree is less sensitive to source mobility and can in part overcome

Multipath routing has been explored in several different contexts. In alternate path routing, each source node and destination node have a set of paths or Multipath which consist of a primary path and one or more alternate paths. It was proposed in order to decrease the call blocking probability and increase overall network utilization. In alternate path routing, the shortest path between exchanges is typically one hop across the backbone network; the network core consists of a fully connected set of switches.

Alternate path routing schemes such as Dynamic Nonhierarchical Routing and Dynamic Alternative Routing are proposed and evaluated in Multipath routing has also been addressed in data networks which are intended to support connection-oriented service with QoS. Alternate or Multipath routing has typically lent itself to be of more obvious use to connection-oriented networks; call blocking probability is only relevant to connection oriented networks. The drawback of this approach is that the cost of storing extra routes at each router usually precludes the use of Multipath routing.

Each multicast group has a unique multicast group address. According to the MAODV specification each multicast group is organized by using a tree structure, composed of the group members and several routers, which are not group member but must exist in the tree to connect the group members. We say the group members and the routers are all tree members and belong to the group tree. "Associated with each multicast tree, the group member that first constructs the tree is the group leader for that tree, responsible for maintaining the group tree by periodically broadcasting Group-Hello (GRPH) messages in the whole network. The group leader also maintains the group sequence number, which is propagated in the network through the GRPH" [8].

The defects of Existing methodology are complexities in link breakage, loss of energy due to low battery and bandwidth loss.

This proposed system we introduce a new multicast protocol, called Energy Efficient Multicast Routing Protocol for MANET with Minimum Control Overhead, which follows a hybrid approach using the grid location service to gather the physical location of the nodes. Use of backup root node provides support in case of primary root node failure. The protocol reduces the total energy consumption as well as improves the performance than a conventional shared tree based protocol by reducing the overhead by maintains the back up node.

The new mechanism is to reduce all the above stated disadvantages by using a novel energy efficient multicast routing protocol. This technique is suitable for MANET. A Shared Multicast tree is constructed for multicast nodes which reduces the overhead of the network. The routes are discovered in the MANET by locating the physical location of nodes that are present in the network using which the route searching and energy consumptions are reduced. (i.e.) The root node searches the near by node for transmission of message by considering the location table.

A new Zone topology concept is to differentiate the nodes which have minimum and maximum hops. In order to overcome link failure in MANET, a back-up node is maintained near the source node which contains all the details of the source node. In the event of failure of source node, backup node sends the failure information to all nodes in the network.

The network nodes are monitored in certain time interval to reduce the link failures that happen due to loss of energy in nodes, a node that has a lower energy will consume the energy i.e. it share its energy with its neighbor node instead of making a sub-path and the data are sent in an compressed form a source to destination reduce the time in reaching its destination.

In Shared multicast tree the protocol dependency on a root node to maintain the group information burdens the root node. Due to this shared tree multicast is particularly not suitable from energy balancing point of view because the root of the tree takes on more responsibility for routing, consumes more battery energy, and stops working earlier than other nodes. This leads to reduced network lifetime and the whole multicast tree is disconnected into a number of partitions which consumes a lot of wireless bandwidth for reconstructing the multicast tree from all these partitions.

The EEMPMO creates the shared multicast tree with backup root node as an alternative to the primary root node. Creation of a backup root node enhances the performance of the multicast tree and also lessens the load on the primary root node. In case of primary root node failure the backup root node takes over, therefore, reduces the dependency on a single root node. This facilitates a great reduction in tree maintenance and tree re-construction overhead.

On considering the stability, battery status and proximity the backup node is selected. Selection of Backup root node is done from the neighbor node. A non-tree member node with slow movement and more power status is chosen to be the backup root node. If the root node does not found any neighbor node with the required criterion then the selection process is delayed by some random time and after that the backup root node search process starts again. The selection process may lead to slight delay but improves overall efficiency of the protocol by selecting a suitable node as Backup node. In case of primary root node failure the backup root node takes over, therefore, reduces the dependency on a single root node. This facilitates a great reduction in tree maintenance and tree re-construction overhead.

If the root node does not found any neighbor node with the required criterion then the selection process is delayed by some random time and after that the backup root node search process starts again. The selection process may lead to slight delay but improves overall efficiency of the protocol by selecting a suitable node as backup node. Selecting a suitable node as backup root node not only serves the purpose of standby root node but also defer the early possibility of searching the backup root node again in case of power failure or movement

3.4.2. ZONE ROUTING

A routing zone is defined for each node separately, and the zones of neighboring nodes overlap. A k-hop routing zone of node S can be defined as a connected topological sub graph, on which node S is aware of the route to any other node .The nodes of a zone are divided into border nodes and interior nodes. Border nodes are nodes which are exactly k hops away from the node in question. The nodes which are less than k hops away are interior nodes.

The proactive scope is reduced to a small zone around each node in the EEMPMO protocol. The radius of the network is large when compared to the Zone radius. In terms of congestion as well as the control traffic, the cost of the Zone routing is cheaper. In addition,the mechanism of the global route is faster , as the process is very small in which the number of nodes are been queried.

A bigger proactive zone can be selected for comparatively stable topology where the updates of topology are done on topology change only. In a limited zone, each node maintains a proactive unicast route to every other node. In the proposed protocol the routing is initially established with proactively prospected routes within the zone and then outside the zone, using diffused routing towards the tree members. Therefore, route requests can be more efficiently performed without exploiting the flooding in the network.

3.4.3. PHYSICAL LOCATION OF MOBILE NODES

The routing performance can be significantly improved by utilizing location information of nodes in communication e.g., if a sender node knows the location of the tree member, it can find out the route to the tree member using constrained routing by forwarding the packet in the relative direction in hopes of getting it there quickly therefore communication delay can be minimized with location information.

A node can use Global Positioning System (GPS) to obtain its geographic location information. The locations of other nodes can be obtained by employing some distributed location service. However, in practice, it is difficult to find/maintain node locations with accuracy in an ad hoc environment where nodes move around. Some well-known location-based routing algorithms are location-aided routing (LAR) protocol, distance routing effect algorithm for mobility (DREAM) and grid location service (GLS).

DREAM in acronym -Distance Routing Effect Algorithm for Mobility .It is a global proactive location service as it flood over the network. The position updates in the whole network proactively which is used by all nodes in the network to build the complete position data base. This scheme causes a lot many overhead and also big requirement of the memory on all nodes. On the contrary, LAR is global reactive location service that causes a pretty long delay for the location updates at far away nodes and also the overhead due to global flooding.

Due to this both the schemes are not suitable in terms of the network congestion and overhead, therefore EEMPMO uses a grid location service to provide location information to all mobile ad hoc nodes and the geographical information thus obtained is used to limit the flooding of packets to a small region.

3.4.5. EEMPMO'S MODIFIED DATA STRUCTURES

No node is a bottleneck as responsibility of maintaining the location service is spread evenly over all the nodes. Failure of a node does not affect the reach ability to many other nodes. Local communication satisfies the queries for the locations of the nearby nodes which also allow operation in the face of network partitions.

The communication cost and per-node storage of the location service grow as a small function of total number of nodes GLS employs a number of nodes as location servers. Distributed throughout the network, which provides location information to other nodes. Although each node has the ability to act as a location node, EEMPMO prefers a node rich in resources like memory and comparatively stable to be location node. In order to facilitate the location service, each node has some data structures in addition to those needed for the routing algorithm.

The data structures used in EEMPMO are amended ones and in addition to the existing ones to improve the Performance of the routing. Each node maintains a localized Location Table (LT). To keep the record of the neighbors within k-hop zone as shown in table 1. Each routing entry contains the IP of neighbor node, location, speed, next immediate hop towards that node, total hop counts to reach to this node and a timestamp indicating when the entry was added or updated.

The number of entries stored in the location table is related to the node's goodness. Score, described below. The second data structure that each node maintains is the scorecard. The node is at providing location information to the nodes outside its zone. Entries are made in the descending order of the score values and only of those nodes having a score value more than a threshold. These nodes represent the location servers.

A small value score indicates a bad location node in providing location information to other nodes, while a high value for the score indicates that the node stores more nodes' locations. It may be initialized proportional to the available size of the node's location table. When the node answers a source node's request, score is increased and when the node moves more than distance from its original place, its entry is removed from the scorecard table. Score is decreased over time through a score decay mechanism. When the score decreases than threshold, the entry will be removed from the table.

The reason for this score decrement is to prevent nodes from expending energy that rarely provide locations, even if they have large capacities. When a source node needs the location of a target outside, it consults its scorecard and sends a request to the highest scoring location node. If a response is not heard after a certain amount of time, the node's score is decreased and the source node asks the next highest-scoring node. When a response is received, the source node increases the node's score.

The amount by which a score is increased should reflect how long a node takes to answer a request, and how up-to-date the location information received from the node is. Besides LT and scorecard, for the purpose of routing information each node maintains Multicast Tree Table (MTT) And Request Table (RT). Each entry of multicast tree table contains the multicast group IP address, multicast group leader IP address, hop count to multicast group leader, next hops and timestamp. This table has entries for all those multicast groups of which group the node is a member.

The Next Hops field is a linked list of structures, each of which contains the following fields: - Next Hop IP Address - Link Direction - Activated Flag The direction of the link is relative to the location of the group leader. UPSTREAM is a next hop towards the group leader, and DOWNSTREAM is a next hop away from the group leader. An entry is added to the table when the node becomes a multicast group member.

An entry in this table contains multicast group IP address, tree member IP address, tree member node's location and a timestamp. In order to exchange location information on the network, four special packet types are exchanged. It contains the IP, location latitude and longitude of the source node, speed of the source node and a timestamp. In response to the HELLO packet the receiving node unicast back an acknowledgement packet.

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