Introduction To Manet Current Challenges In This Field Computer Science Essay

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The commercial arena has done excellent marketing of the 3G and 4G technology. To sustain the growth and development of these novel technologies, the next generation of mobile devices shall require the support of infrastructure based communication networks as well as non-infrastructure based networks. Mobile Adhoc Networks (MANET) falls into the second group. The MANET technology is a self organizing network of mobile devices, in the MANET architecture each node mimics a router and transfers data to the subsequent node based upon the data supplied to it. In the MANET architecture, some intricate nodes (usually one node or more than one node) may be connected to the internet. A MANET reduces dependency on supporting infrastructure (like cell sites) but brings with it many new challenges, the primary challenge being that each node must be periodically supplied with data which allows it to route the traffic properly.

In this document we shall focus upon certain aspects of MANET. We shall highlight the current trends in this technology, issues that have to be dealt with and future prospects[1].

The origin of MANET technology lies in early military applications. The defense forces wanted to set up networks in remote, hostile locations. Construction of base stations in such an environment would be against the principle of tactical sensibility. So the defense forces were looking for a technology which will allow a rugged network to be set up, without being dependent on any supporting infrastructure. MANET technology gives prospect to the idea of pervasive computing [2]. Also known as ubiquitous computing, this concept indicates that virtually any component, which has an integrated chip, can be a computer. Thus the computing environment would move beyond the realm of traditional PC’s. Items like coffee mug, clothes, human body, tools can be embedded with micro chips and be part of an infinite network of other devices. This can potentially lead to the creation of an omnipresent networking system.

The IEEE 802.11 standard establishes various working modes, which allow wireless mobile components to communicate with each other. This standard can be very helpful in development of wireless adhoc networks.

The MANET technology derives its features from Mesh Networking, Multihop Wireless Networking and Mobile Packet Radio Networking. It is a self configuring system of mobile nodes. The system dynamically forms a network without preexisting infrastructure [3, 4] and the nodes exchange information. The network acts like a peer-to-peer paradigm. The intensity of connection between the nodes can vary from time to time and sometimes the connection strength can disappear altogether. Salient features [5] of an adhoc network are: it supports connectionless Internet Protocol communication, it can alter its configuration with change in topology, in this system nodes can be hosts as well as routers, mutual trust between the participating nodes has to exist, the system has limited security and limited energy sources.

A MANET allows dynamic addition and removal of nodes from the network [4]. The power supply to each node is limited. The power consumption of each node can be categorized into 3 parts: power consumption for data processing in the node, power consumption to transmit its own information to a destination and power needed when the node is used as a router. Energy usage is an important issue with regards to a MANET since energy source is limited.

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Figure2- MANET Protocol Stack [1]

The author in [1] explains the basic architecture of IEEE 802.11 MANET. Figure 2 shows that and additional layer of MANET is added to the traditional TCP/IP suite. The basic functionality of this layer is to route Internet Protocol packets in an environment where no base stations are available. The IEE802.11 standard offers 2 types of services: Distributed Coordination Function (DCF) [6] which is a contention based service and Point Coordination Function (PCF) [7] which is a contention free service. The DCF uses a CSMA/CA scheme while the PCF uses a polling scheme. In the adhoc network the DCF is used more often than the PCF. In the 802.11 MANET, the adhoc stations are said to form IBSS (Independent Basic Service Set). In this setting, any station which is in the range of another station can communicate with it and no monitoring is required from a central source.

The general characteristics of a MANET [4] are:

Autonomous: In the MANET architecture each mobile terminal is autonomous. A terminal can function as a router as well as a host depending upon the conditions. Hence it is difficult to distinguish between switches and end points in the MANET network.

Distribution of work: In the MANET architecture, there is no single controlling authority. All the participating nodes are equally important and the work load is distributed among them. All the nodes mutually decide the working of the network and various functions to be performed.

Multihop Routing: The IEE802.11 standard is highly proficient when it comes to single hop routing. But in the case of MANET, many times multi hop routing is desired. Single hop routing is only possible when the subsequent transmission stations are within the range of 100-200 meters. In the case of multi hop routing, the message is carried from the source node to the destination node via multiple intermediate nodes [9].

Dynamic Network Structure: The nodes in a MANET are not stationary; they are expected to move about. This may lead to the formation of a dynamic network at an instance of time. Without standardization and optimization principles, such a scenario can cause poor connectivity.

Periodic Changes in Link Capacity: A common problem in wireless connectivity is high bit error rates. Naturally, it would be more profound in a MANET where many parameters are dynamic and instantaneous. In many cases, the path between any 2 nodes in the network will comprise of multiple transmission links, in MANET these transmission links can change in an arbitrary manner, thus the bandwidth is subjected to fluctuation.

Lightweight nodes: The nodes in a MANET are lightweight in all aspects. In the initial part of the paper, the authors mentioned that nodes in a MANET have access to low energy sources. Additionally, the nodes have slow processors and limited memory. Keeping this in mind, optimized algorithms have to be designed which shall manage the various mechanism in a MANET.

The applications [1] of a MANET are:

Commercial Applications: MANET would be useful in emergency operations. Example- Consider an area which has been struck by earth quake and has no infrastructure or damaged infrastructure; a simple network of hand held devices among rescue workers would be very useful.

Applications at Local Level: Adhoc networks would be beneficial in corporate conferences, class room studies and home networks. In the local spectrum, ad hoc networks can be used to autonomously link laptops, PC’s and embedded systems.

PAN (Personal Area Network): PAN is an important application field for MANET. Combining MANET with satellite based information delivery, targeted system can be developed. These systems will allow quick deployment of resources in the case of safety operations.

In recent times more importance has been given to wireless communication strategies. Keeping this in mind, a Working Group (WG) for MANET has been established within the Internet Engineering Task Force (IETF) [10, 3]. This group studies IP based protocols on ad hoc networks, and hopes to standardize routing protocol functionalities, mainly for infrastructure less dynamic networks.

Till 21st August, 2008, the WG for MANET under the IETF has suggested 4 protocols for experimental RFC status. These are: Adhoc On Demand Distance Vector (AODV) Routing protocol, Optimized Link State Routing (OLSR) protocol, Topology Dissemination Based on Reverse-Path Forwarding (TBRPF) protocol and Dynamic Source Routing (DSR) protocol. AODV, OLSR, TBRF and DSR have been submitted in RFC 3561, RFC 3626, RFC 3684 and RFC 4728 respectively. These protocols are designed in a manner that they are compatible with light weight devices which have low memory and low computational power. The WG will develop 2 tracking protocols: Reactive MANET Routing Protocol (RMRP) and Proactive MANET Routing Protocol (PMRP). The WG is conducting investigations based upon the following design principle. It hopes to construct routing tables in which each node will know about its neighbor nodes and it will also know about the nodes which are near to its neighbor. Possessing this knowledge, the participating nodes will mutually generate routing tables that can send packets through the network in an effective manner.

RMRP and PMRP protocols would be thoroughly studies by the WG. If common features are deduced then the WG can hope to produce modalities which have combined features of both of them. The WG has suggested a protocol; Neighbour Hood Discovery Protocol (NHDP) which allows nodes to detect other nodes 1 and 2 hops away. They have suggested a modality, Management Information Base (MIB) which defines a collection of tools for managing routes on a mobile network. The IETF is doing extensive research and is considering various obstruction parameters that can affect the network like jitters, noise, interference etc. The research effort has achieved considerable progress but vital issues still remain; till date there is no clear picture as to how MANET technology will work in real environments on a daily basis [11]. Feedback from users is missing since there is no deployment of multihop adhoc networks. However, in the past few years a lot of research effort is being undertaken by academic and corporate groups.

MANET incorporates several challenges which must be met before a large scale deployment can be expected. They are:

Addressing issue: Nodes in a MANET must be identified by their IP address. The nodes need to construct precise addresses for them in order to communicate with conventional devices. The IPv4 address configuration is supported, but only through Dynamic Host Configuration Protocol or manual configuration. Another problem with the IPv4 scheme is that it will run out of addresses eventually [12]. Thus MANET networks using IPv4 scheme will face problems. ZeroCofig address configuration technique has solved the problems to a great extent, but this technique is not compatible with medium or large networks [13, 14].

Routing Management: Ipv4 based routing protocols like Routing Information Protocol (RIP) of Distance Vector Algorithm [15] and Open Shortest Path First (OSPF) of Link State Algorithm is not compatible in adhoc mode. Describing optimal routing protocols for MANET has been an active research interest in the past 10 years.

Reliability Issues and Security Issues: In the MANET architecture, many of the proposed protocols work on the basis of mutual trust between the nodes [16]. The routing protocols are expected to address the issues of fundamental security principles of Confidentiality, Integrity and Availability. The routing protocols are also expected to address the issue of location secrecy. Routing protocols must be in a position to protect themselves against internal attacks as well as external attacks.

Quality of Service: In [1] the authors mention that importance has to put on a new QoS model with regard to the MANET. Different categories of QoS allow optimum implementation of multimedia technology in the MANET [17].

Internetworking: In the future, internetworking between MANET and fixed networks is expected. Routing protocols managing such heterogeneous systems is a prospective challenge.

Kernel Barrier: Novel algorithms have to be established to efficiently transfer information from the source to the destination without incurring errors. Novel models are needed to describe MANET features. Deterrents such as variable wireless link quality, multi-user interface, change in topology add complexities to routing protocol design.

MANET will benefit from the extensive features of IPv6 scheme. The features of Ipv6 scheme which will be advantageous to the MANET architecture are: increased address space providing global reachability, allow stateless configurations for describing varied routing protocols, integrated security features, embedded multicast feature, scalability and enhancement of network performance. The integration of IPv6 scheme into the MANET architecture issue fresh challenges which open the prospect for future research and future technological feats.

In conclusion, a novel efficient IPv6 MANET has to be designed. Studying the current IPv4 MANET will give clues to the computer scientist and researches as to what parameters they should improve upon. There are many relative aspects that have to be studied in depth before commercialization of MANET technology is possible.

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