Current Protocols Of Ad Hoc Wireless Routing Computer Science Essay

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: Introduction and Motivation

Introduction:

With the rapid development in the connectionless routing the development of 'wireless routing protocols' has recently been a hot research area. One issue is that 100% geographical coverage is not possible in order to fulfill connection requirement in a mobile situations.

This is an era of wireless technology, to be more specific new generation used to having all time connection for mobile networks as they cannot survive without it. Furthermore they expect instant access everywhere, wherever they go. They demand on speedy run message delivery and reception.

Consumers, mainly youngsters want to use continuous communication between friends so plan their course of action accordingly. Sometimes they do not receive or not able to send messages because of poor network connection. They just don't wait to be available a network they just want it with speed and quality as this world is a full of competition they do not want to miss any opportunity in the life. According to all forums of available networks many times costumers experience problems with delayed messages. The existing network sum times not able to provide best quality or speed. And this has made all the leading telecommunication networking companies to invest and research on increasing the performance, capacity, simplicity etc by modifying the current protocols. Store and Forward system is the most promising application to Ad HOC Wireless Routing Protocols which can make the remove these problems.

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There are other examples too which include establishing survivable, efficient, dynamic communication for emergency/rescue operations, disaster relief efforts, and military networks. 

Figure I‑1 Example about Need of Continuous Communication

There are some existing protocols available but these protocols have some limitations which limit it from attaining maximum mobile coverage area. This research is to study these issues and overcome it by examine the possibility of modifying protocols. This in turn will give a new method to attain the continuous connection between nodes which is just a dream at this point. If successful this will completely revolutionize the way of node connections.

As this is a theory and simulation based research work, the results of the study will be submitted with the successful practical implementation of the work.

Project Motivation:

Due to technological advances communication industries are ever increasing for wireless communication between mobile users. The major challenge is behavior of how mobile node cooperates in a co-ordinate way to increase the Network Coverage Area. [Virtual Access Points for Vehicular Networks].

Due to dropped connection between two nodes the packet is not able to reach at the receiver side. Current protocols require continuous connection. This project examines the possibility of modifying protocols to include disconnected message passing.

The following concept is considered for research questions:

Store and Forward

There is increasing demand of amount of data to be sent immediately at high speed among many sites. The issue of high speed data is solved by designing communication protocols. Connectionless protocols are useful in applications where a small amount of data is transmitted over a reliable channel. [A PERFORMANCE COMPARISON OF CONNECTION-ORIENTED AND CONNECTIONLESS LLC PROTOCOLS IN A HIGH-SPEED SATELLITE DATA NETWORK]

An ad hoc routing protocol is a convention, or standard, that controls how nodes decide which way to route packets between computing devices in a mobile ad hoc network. Recent search studies on wireless routing protocols indicate that many routing algorithms were proposed for mobile ad hoc network (MANET) but their performance is usually limited under high mobility or various node densities. A connectionless algorithm even encounters a local maximum problem (also called void problem) under low node density.  The problem causes a data packet cannot be transmitted to the destination Mobile Node (MN).

Project Aim and Objectives:

AIM

The overall aim of this project is to examine the possibility of modifying protocols to include disconnected message passing using "Store and Forward" concept and implement changes by testing functionality on simulator.

OBJECTIVE

For the purpose of achieving the aim in a smooth manner, the project objectives is subdivided in to different stages with objectives which fit with those different stages of the work. With the completion of each objective, a milestone will be achieved and the project will be moving towards it's over all completion.

The Sub-project objectives are as follows:

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To research and study the current protocols of Ad HOC Wireless Routing Protocols: Achieving this objective would provide good background knowledge in relevant areas and will also help in understanding the problems that may be encountered and how others have dealt with similar issues. It also helps in understanding how different protocols differ from each other and how these different protocols would aid in achieving aim of the project.

To develop a simulation model: A simulation environment is created using coding and the results are obtained under the simulated environment.

Evaluation: The results obtained from the simulation are compared with the theoretical expectation and the other possible outcomes encountered during the process will be proposed either as an advantage or a disadvantage.

Conclusion and Inference: Based on the final evaluation a conclusion is drawn whether the Store and Forward is advantageous or not.

Presentation: A final presentation of the overall research and simulation is created for display and seminar purposes.

Report Generation: An overall report is created to baseline the research work as a hardcopy for further study and future references.

Research Methods and Techniques:

To study whether the modification for Store and Forward concept is possible or not is solely based on the simulation and output of the Simulation. For this purpose an appropriate simulator must be chosen that supports these protocols. No existing simulators support this as such. Opnet 14.5 and QualNet do support Ad HOC protocols.

In this model following points are considered for research method.

Study current protocols

Research changes required for a Store & Forward system.

Implement changes and test functionality on simulator.

Other than this an overall project plan is created using Microsoft Project to have the project neatly time lined with milestones. A Gantt chart is formulated for this purpose. For the purpose of creating presentation and Report, Microsoft Power Point and Microsoft Word are used.

: Literature Review and Related Works

Wireless communication is succeeding tremendously and spreading progressively in our daily life. The major factor is messaging. End-to-end connectivity is not a natural property of ad hoc networks. For in-stance, nodes may vary their transmission power, nodes may move, nodes may enter the sleep mode, or nodes may suffer from hardware failures. As a result, the network structure changes dynamically and this may lead to undesired situations of nodes becoming disconnected from parts of the network [A Tandem Queuing Model for Delay Analysis in Disconnected Ad Hoc Networks] , because of the short lived connectivity in the network

Due to limited radio transmission range, sporadic node densities and power limitations, transform mobile ad hoc networks (MANETs) into intermittently connected MANETs (ICMANs) where data routing process is disrupted in the absence of end-to-end routing path. In a bid to address this problem, various "store-carry-forward (SCF)" routing algorithms have been proposed in the literature that exploits the mobility and storage space of the nodes. In majority of these algorithms, performance is quantified in terms of delivery probability. Unfortunately in a mobile environment like ICMANs where there is uncertainty about the future state of the network, delivery probability alone cannot provide a good enough measure of message selection, even under community based mobility conditions containing historical statistics of correlated movement.[A Fuzzy Logic-based Delivery Framework for Optimized Routing in Mobile Ad Hoc Networks]

Mobile Ad Hoc Network (MANET)

Ad Hoc wireless network is a collection of devices that have wireless transceivers and that provide store-and-forward functionalities on top of the physical and medium access protocols in use, as needed to enable multihop wireless communications (see Fig. 1). Such devices can thus be classified as routers in the resulting wireless network, which is also known as a MANET. [IP Links in Multihop Ad Hoc Wireless Networks]

Figure II‑2 MANET communication.

The light grey area indicates the radio coverage area of each MANET interface. Store-and-forward functionalities are provided to achieve multi-hop radio communication, for instance between N1 to N5, which cannot communicate directly since they are out of radio range from each another.

Routing

Ad Hoc wireless network consist of source and destination interconnected by routers. In wireless communication network packet traverse the network between source and destination.

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Routing establishes the mechanism by which a packet traverses the network

A "route" is the sequence of relays through which a packet travels from its source to its destination

Many factors dictate the "best" route

Typically uses "store-and-forward" relaying

Network coding breaks this paradigm

Nodes store messages for a maximum amount of time and deliver them to close-range nodes, with storage time and maximum hop count as limiting factors, so that messages do not live forever within the network and congestion can be reduced. Newly received messages are added to the message repository, if the message is not yet in there. Messages can be identified by sender address, message payload message authentication code (MAC), hop count, among others. This constitutes a multicast-like procedure in order to synchronise message repositories of nodes within a certain distance.[ Mobile Learning by Using Ad Hoc Messaging Network].

Current Protocols

An ad hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. A number of routing protocols such as Dynamic Source Routing (DSR), Ad Hoc on-Demand Distance Vector Routing (AODV) and Destination-Sequenced Distance- Vector (DSDV) have been implemented. [Influence of Routing Protocols in Performance of Wireless Mobile Ad Hoc Network]

There are two types of protocols Table-driven and Source-initiated On-demand protocols.

And sub parts of these protocols are shown in the fig. 2.The description several routing protocols proposed for ad hoc mobile networks and classification of the protocols according to the routing strategy is as follow:

Figure II‑2 Ad Hoc Routing Protocols.

In terms of the way in which routers obtain information, routing protocols have been classified as table-driven and on-demand. [Source-Tree Routing in Wireless Networks]. It's a Table driven protocol, in this each node maintains a table that contains the next hop to reach all destinations. To keep the tables up to date they are exchanged between neighbouring nodes at regular intervals or when a significant topology changes are observed.[ Influence of Routing Protocols in Performance of Wireless Mobile Adhoc Network]. The concept all routing protocols is summarized as below:

2.1 Destination-Sequenced Distance-vector Routing (DSDV)

Each node maintains every possible destinations

Common in table-driven

Tables

Routing Table + table to keep track of incremental updates

Periodic updates

Full Dump

Incremental updates

Drawback

Periodic updates regardless of the # of changes in the topology

2.2 Cluster Gateway Switch Routing (CGSR)

Hierarchical address space

Nodes are grouped into clusters.

Special nodes

Cluster head

Forwards packets to gateways on behalf of source nodes

Dynamically elected

Gateway

nodes within the communication range of two or more cluster head

Tables

Cluster member table: (node -> cluster head)

Routing table: (cluster head -> next hop)

Using DSDV to broadcast the member table periodically

Drawback

Too frequent cluster head selection can be an overhead

Cluster nodes and Gateway can be a bottleneck

Figure II‑3 CGCR Example.

2.3 Wireless Routing Protocol (WRP)

Tables

Distance table

Routing table

Link-cost table

Message retransmission list (MRL) table

Periodic hello message

To keep track of alive neighbors

Loop Free

By forcing each node to check consistency of predecessor information reported by all it neighbors

Drawback

4 tables requires a large amount of memory

Periodic hello message consumes power and bandwidth

2.4 Ad Hoc On-demand Distance Vector Routing (AODV)

On-demand version of DSDV

Pure on-demand routing acquisition system

Nodes out of the routing path doesn't maintain any information about the path

Assumes a symmetric link

Route reply packets use the reverse path of route request packets

Route Timer : remove stale entries

Supports multicast

2.5 Dynamic Source Routing (DSR)

Route Cache : maintains source routes

Append visited node id into a packet

Assumes an asymmetric path

A destination node sends another Route request to the source node to find a reverse path

Reply is piggybacked on the request packet.

Advantage

No periodic hello message

Fast recovery: cache can store multiple paths to a destination

Disadvantage

Scalability : packet size grows with the network size

2.6 Temporally Ordered Routing Algorithm (TORA)

"Height"

Logical metric to build Directed Acyclic Graph (DAG) rooted at the destination.

Timing is important

Because it assumes the synchronized clock among nodes

Therefore, it relies on external time source such as GPS

Advantage:

Supports multiple paths to a destination (like DSR)

Disadvantage:

Reliance on global time synchronization

Comparison Between On-demand and Table-driven Protocol

The following table exactly compares the differences between On-demand and Table driven Protocol.

Parameters

On-demand

Table-driven

Availability of routing information

Available when needed

Always available regardless of need

Periodic route updates

Not required

Required

Coping with mobility

Use localized route discovery

(ABR and SSR)

Inform other nodes to achieve a consistent routing table

Signaling traffic

Grows with increasing mobility of active routes

Greater than that of on-demand routing

Illustration of Store and Forward Based Packet Delivery

In the MANET that can cover 100% geographical area with distinct communication conditions packets can be delivered efficiently and adaptively to the local networking situations with Store and forward based packet delivery system.

In MANETs of low node density, the distribution of mobile nodes can be so sparse that nodirect source-to-destination path can be found most of the time. Traditional routing protocols that only forward packets in connected paths are not suitable for sparse MANETs due to the very weak connectivity. To make communications viable in sparse MANETs a special routing solution, store-and-forward based routing, has been proposed for packet delivery in mobile networks of sparse topology by making use of the intermittently connections between mobile nodes. Fig. 2.4 illustrates the principle of store-and-forward based routing in a sparse MANET of 3 nodes. As shown in Fig. 2.4, in the network of node s, r, and d, there is no connected path between node s and d at the time (e.g. 10am) when s has some packets destined to d. Node s would hold these packets temporally and forward them to any passing-by nodes (e.g. to r at 10:30am). Given that the nodes do not stop moving in the area of limited size, either node s or r may (e.g. at time 11am) meet d after a period so that the packets could be offloaded at their estination. The distribution of the length of the time period is determined by a number of

factors such as the speed of mobiles, the size of the network area and the node density. There is a possibility that the time period is infinite and a packet will not be able to reach its destination by the time that it is dropped from the buffers.

S

S

R

11 AM

10.30 AM

10 AM

R

R

S

D

D

D

Based on the concept of store-and-forward, numerous routing schemes have been developedin recent studies for networks that share the same properties of being sparse and mobile(e.g. Intermittently Connected Mobile Networks or Delay Tolerant Networks). These proposalscan be broadly classified as deterministic methods [44] [45] and probabilistic methods. A more detailed survey of routing in sparse MANETs/Delay Tolerant Networks (DTNs)can be found in [46]. Deterministic methods

In the deterministic approaches, an end-to-end route is determined before messages are transmitted by the source. The determination of the delivery path is depend on the available knowledge on the characteristics of the network topology and the trajectories of mobiles at a specific time (or time interval). An example deterministic routing for sparse MANETs is the space-time routing framework proposed in [44]. The space-time routing forward packets in pre-specified schedules and paths that are designed according to the a priori knowledge of nodal trajectories. A similar routing framework proposed in [45] incorporates several strategies

that can be used in accordance with the amount of time-varying topological information (or knowledge oracles [45]) available. For example, if the information on aggregate statistics of the inter-node contacts is known, a routing table can be constructed using the Dijkstra algorithm with time-invariant edge costs and the average waiting time.

Probabilistic methods

Probabilistic methods are proposed for more common cases that the network evolution is not predictable nor known a priori. In this class of methods, intermediate nodes decided independently whether to forward packets at realtime, according to various policies that can be unconditional forwarding [9] or conditional forwarding based on QoS targets [10], utility threshold or mobility pattern of the contact [47], etc. Epidemic routing [9] is the simplest probabilistic method that allows every relay node to forward packets to their contacts unconditionally. Epidemic routing can quickly disseminate packet throughout a network and no oracles of the network are needed. However, unconditional forwarding often leads to high bandwidth wastage. More bandwidth economical probabilistic methods such as only forward packets if pre-defined conditions are met. For example, PROPHET [48] only forward packets to contacts having higher chance of meeting the destination. Mobyspace based routing only replicate packets to neighbours having similar mobility pattern to the destination. Multi-copy routing [10] allows packets to be relayed as long as the total number of packet replicates has not reach a preset limit, the replication factor. Complementary techniques such as erasure-coding [49] [50] can be also applied for the probabilistic methods to reduce the cases of long delivery delays

without increasing traffic overhead.

Routing Protocols Performance

An ad hoc wireless network is shaped by a collection of nodes which can communicate with one another by wireless links without a fixed infrastructure, such as base stations or towers [4]. Each node can connect to its neighbouring nodes only, because of limited radio broadcast coverage. When any two nodes are not in the same radio coverage area, communication between them requires a multiple-hop radio connection, relying on other intermediate nodes to link them. These nodes have a mobility facility which enables them to join and leave the network as required.[ Architecture of EHARP Routing

Protocols in Ad Hoc Wireless Networks].

Many protocols have been proposed for mobile ad hoc networks, with the aim of achieving efficient routing [2, 11-17]. These protocols differ in the approach used for searching for a new route and/or modifying a known route when hosts move. In designing routing protocols for ad hoc networks, it is essential to maintain the flow of control packets between communicating nodes as well as establishing new links. However, the flow of control packets should be kept to a minimum. This is because increasing the number of control broadcast packets by flooding is very costly and results in serious problems. Such as generating excessive redundant control message overhead, contention and collision. The latter is due triggering a huge number of packet forwarding that ultimately results in the breakdown of the entire network [12].

In an ad hoc wireless network, each node works as a host as well as a router and will propagate packets for other nodes in the network which are not within direct wireless broadcast range of one another. Every node participates in the network administration and routing scheme, owing to the constantly changing network topology. According to

routing protocols, each node can discover multiplehop paths through the network to any other node. These can generally be classified according to the routing information update mechanism into three categories: proactive, on-demand and hybrid. Proactive protocols, also known as table-driven protocols, require every node to maintain one or more tables in order to store the network topology and routing information. This information is

updated frequently by periodically exchanging routing information, which must thus be updated periodically for example Destination Sequenced Distance-Vector (DSDV) [6]. By contrast, reactive protocols establish necessary routes when required (on demand) by using a route discovery process andsource, so unlike proactive routing protocols they do not maintain information on the network topology and routes to each destination of the network for example Ad hoc On-demand Distance Vector (AODV) [7] . Hybrid protocols combine features of reactive and proactive protocols in order to offer routing solutions. They operate by adapting to the specific conditions and are in general the most advantageous option for example Zone Routing Protocol (ZRP) [18].

Routing and mobility characterization are two of the most important aspects of mobile ad hoc networking. In MANETs, most of the building blocks of the communication system need to be aware of the characteristics of mobile movements in order to improve their effectiveness and adaptivity. And without distributed routing protocols to cope with the frequent topological changes, communications in MANETs would not have been possible. Recent advances in these two areas have brought many solutions that make communications in ad-hoc networks a reality. For example, protocols such as AODV [6], EDSR [7] and ZRP [8] were proposed to route packets in cases of high node density and Epidemic [9], Spray&Wait [10] were developed for networks of very low node density. Mobility models (e.g. Random Waypoint, Random Walk and City Section, etc.) [11] and estimators (e.g. Doppler-frequency-based) have also been developed to capture/predict the characteristics of the movements of mobiles, based on which the stability of a wireless link, a routing path or the performance of communications in a MANET can be evaluated.[RESOURCE-EFFICIENT STRATEGIES FOR MOBILE AD-HOCNETWORKING]

Conclusion

Inference

Considering the overall perspective in all these various literatures discussed above, store and forward protocol is used in Ad Hoc Wireless Network with the simple objective to enhance the disconnected message passing. However it is also noticeable that the limitations of Store and Forward protocol do exists in Ad Hoc Wireless Network, but there might be some possible modification can be performed for connected message passing. According to my expectation the limitations will cancel out and the theoretical maximum modification could be attained. My research is aimed at studying the advantages current existing protocols with the help of simulations.