Overview of Temporally Ordered Routing Algorithm and QOS Components in MANETS

Overview of Temporally Ordered Routing Algorithm and QOS Components in MANETS

Jahangir Khan (Sarhad University of Science and Information Technology Peshawar, Pakistan) and Abou Bakar Nauman (Sarhad University of Science and Information Technology Peshawar, Pakistan)
DOI: 10.4018/978-1-4666-0321-9.ch006
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Abstract

TORA is a highly adaptive routing protocol that provides loop free routing of data packets in ad hoc network at every instant. Each node of network has the capability to contain information about its local topology changes and regular coordination with their neighbour nodes in order to detect partitions occurs in network. In Ad-Hoc networks, multicast communication is not ideal due to the frequent nodes mobility and failures. Such problems in transmission of data become reasons for increased delays and decreased throughput, and also sudden changes in delay, traffic, and link breakage occur due to nodes mobility. The network parameters like network size, number of nodes, number of hops per route, traffic patterns (bits/packets), link capacity, mobility trajectory, and frequency of sleeping nodes do have great results on the performance of routing protocols in the mobile ad hoc networks. TORA has three basic route functions: establishment, maintenance, and erasing. In TORA routing protocol, each node has capable to contain a structure of network describing node’s height and status of all connected links. The importance of these heights in TORA routing protocol are that a node in network may only forward data packets downstream instead of upstream. TORA are more appropriate for QOS in ad hoc networks with a higher mobility and data transfer rate.
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Overview Of Tora

Temporally Ordered Routing Algorithm (TORA) is a source initiated on-demand routing protocol presented by Park and Corson in 1997 for wireless mobile ad hoc network. TORA is an efficient, highly adaptive, and scalable routing protocol based on link reversal algorithm. TORA provide multiple routes to transmit data packet between source and destination nodes of mobile ad hoc network. TORA is an adaptive routing protocol for multi-hop networks that contains different attributes such as; distributed execution, loop free and multi-path routing. This routing protocol is designed to reduce communication overhead by adapting local topological changes in ad hoc network. Another smart function of TORA routing protocol is the localization of control packets to a small region (set of nodes) near the occurrence of a topological changes due to route break. Therefore each node of network needs to contain its local routing and topology information about adjacent (one hop) nodes. [Anna, 2003]

TORA has three basic functions

  • 1.

    Route Establishment

  • 2.

    Route Maintenance

  • 3.

    Route Erasing

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1. Route Establishment

TORA routing protocol performed route establishment function when a source node in network wants a route to transmit data packets to destination but does not contain information about directed link. Route establishment between source and destination nodes are carried out by two types of packet, i.e.

  • QUERY (QRY)

  • Update (UPD)

For route discovery TORA establishes a destination oriented directed acyclic graph (DAG) by assigning directions to links in ad hoc network rooted at destination. Thus TORA assigns directional heights to links in network so as to transmit data packets from a higher source node to a lower destination node.

Figure 1.

Directed acyclic graph rooted at destination (Larsson, 1998)

TORA establish multiple routes quickly to destination. To establish a route, source node broadcast a QRY packet containing destination address through network. The QRY packet propagates through mobile nodes of ad hoc network until it reaches either destination or an intermediate node which has a rout to destination. Each node in network has a height with respect to the destination that is computed by TORA routing protocol. These heights are assigned to links based on direction towards destination. The destination or intermediate node that terminates QRY packet broadcasts UPD packet containing its distance/height with respect to destination (the height is zero at destination node). Each node that receives UPD packet sets its height to a value greater than height of neighbour node from which it received UPD packet. This series of directed links creates DAG in network rooted to destination.

In TORA routing protocol, each node has capable to contain a structure of network describing node’s height and status of all connected links. The importance of these heights in TORA routing protocol are that a node in network may only forward data packets downstream instead of upstream. Each node height metric is represented by a quintuple (τ, oid, r, δ, i) which includes the following values.

  • τ : Logical Time of a link failure

  • oid : Unique ID of the node that defined the reference level

  • r : Reflection indicator bit

  • δ : Propagation ordering parameter

  • i : Unique ID of the node

Consider following Figure 2 where source node A wants to establish a route to destination node G to send data packets. A QRY packet is propagated by source node A through network. The QRY packet is forwarded by intermediate nodes B, C, D, E, and F to reach destination node G, or any other node which has route information to destination.

Figure 2.

QRY packet route establishments in TORA

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