The Mobile Computing is experiencing a revolutionary change with the widespread availability of wireless communication devices like mobile phones, PDAs and laptops. The present world is moving from the personal computer age that is one computer per person to the Ubiquitous computing age where the user utilises a several electronic devices and exploits the required information wherever and whenever needed. (http://www.docstoc.com/docs/8650494/Mobile-Ad-Hoc-Networking-An-Approach )With the advancements the software and hardware techniques have resulted in mobile hosts and wireless networking common and miscellaneous. There are two kinds of wireless mobile units to communicate with each other. They are 1) Infrastructured wireless mobile networks and 2) Infrastructure less wireless mobile networks. Examples of Infrastructured wireless mobile networks are like GSM, UMTS, WLAN and example of Infrastructure less is Mobile Ad hoc Network. Mobile Ad hoc networks are the networks that form dynamically without using any centralised controller or any network infrastructure. This kind of peer to peer system infers that each node in the network can either act as a data end point or an intermediate repeater. Each node in the network should work together in order to improve the reliability of the network, and therefore the network communications. These types of networks are called the mesh network as the topology used in the network looks similar to the mesh. The terminated communication paths delivered by the ad hoc mesh networks will improve the fault tolerance for the network and the capacity of data packets to hop from one user to another effectively spreads the network coverage area and gives an answer to overcome the non-line of sight (LOS) issues.
The existing issues of the mobile applications for the mesh networks as changes to the network topology are widespread. Such cases demands the use of the Mobile Ad hoc Networking (MANET) technology to make sure the communication links are updated quickly and accurately. MANETs are self-forming, self-maintained and self-healing, and also permits the extreme network flexibility. Hybrid MANETs, formed with the fully self-contained MANETs tied to an IP-based global or local network. ( http://www.novaroam.com/Inside.asp?n=Technology&p=MANET )Earlier the Mobile Packet Radio Networked is used in the military can be called as the predecessor for MANETs which improves the IC technology, high tech communication equipment. In the battle field of military operations there will be the problem in order to have a infrastructure based communication thus the MANET gets importance which operates even without using the pre-existing fixed network infrastructure.
BACKGROUND
In the twenty first century, IT mainly relies on wireless technology except in some cases like the traditional mobile and cellular networks, which requires the infrastructure for example the base station, routers and so on. An ad hoc mobile network is a transient network which is a combination of dynamically collected wireless mobile devices without using the static network infrastructure. The mobile devices of a MANET themselves act as networks and co-operate with the other devices or nodes to resemble the functionality of a fixed network infrastructure which enables the information exchange between the user's mobile devices. For the successful operation bandwidth is needed which is the only external source required. The directly connected nodes in the network utilize the wireless LAN technologies for communication whereas the nodes that are not directly connected communicate using intermediate nodes. This feature of MANET greatly helps to the evolution of the mobile phones and the PDA's equipped with the wireless infrastructure. Initially the MANETs are mainly used to provide or to improve the communication or survivability in the battle field. In the battle field the military operations will be dynamic so that military cannot depend on the access to a fixed pre-planned communication set-up. MANETs are gaining importance as they provide the network services even without having a pre-fixed network. Also the ad hoc nodes in a network can be connected to the main network using a dedicated gateway device facilitates the IP networking services where there is lack of Internet services. These advantages of MANET make it attractive for the future evolutions in the field of wireless networks. http://www.ece.ncsu.edu/wireless/Resources/Papers/adhocSurvey.pdf
RESEARCH
MANET concept:
Mobile Ad Hoc Network is an autonomous network system in which the mobile nodes connected with wireless links move randomly and in turn acts as the routers for the nodes that are not directly connected. There are quite different types of traffic types in ad hoc networks than in the conventional infrastructure wireless network, like
Peer-to-Peer
Remote-to-Remote
Dynamic Traffic
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Fig:1 http://www.google.co.uk/url?sa=t&source=web&cd=13&ved=0CCsQFjACOAo&url=http%3A%2F%2Fciteseerx.ist.psu.edu%2Fviewdoc%2Fdownload%3Fdoi%3D10.1.1.104.333%26rep%3Drep1%26type%3Dpdf&rct=j&q=mobile%20ad%20hoc%20network%20technology&ei=U9BgTOTgK6C60gSgntiQCQ&usg=AFQjCNHRqKu-X75QB4Yiz5ZvvkAwG66agA&sig2=OPcHsM2Hmph0S4g-XN9ZPg&cad=rja
MANET is becoming popular because of the following features
Autonomous Terminal
Dynamic network topology
Fluctuating link capacity
Multihop routing
Light-weight terminals
Distributed Operation
The status of MANET:
In the early 70's itself ad hoc networking is deployed in military and it has grown rapidly commercially after it got developed in wireless communications. The research is going on by IETF (Internet Engineering Task Force) to find the ways of developing candidate standard internet routing support for the mobile devices, wireless IP autonomous segments and also to develop a system to run IP based protocols in ad hoc networks. IEEE 802.11 is further increased the research in this field. Research in the ad hoc networking attractive the attention of the academia, industry and also government in order to solve the complex issues posed by the ad hoc networks. For instance the international conference MobiHoc (The ACM Symposium on Mobile Ad Hoc Networking & Computing) held by IEEE and ACM [1].
Types of Ad hoc network:
There are two kinds of wireless Ad Hoc Network. They are
Quasi-static Ad Hoc Network, is the network in which the mobile nodes are may be mobile or static as the power controls and link failures the resulting network topology may be so active for example the Sensor Network.
The mobile ad hoc sensor network follows a wide spread operations and less composite setup procedure in comparison to the usual sensor networks that communicates directly with the centralised controller. The mobile ad hoc sensor network can also be called the hybrid ad hoc network consists of a number of sensors are wide spread in a large geographical area. In which each sensor will have some level of knowledge of handling the signals to transmit the data and also handles the mobile communication. The mobile ad hoc sensor network is attracting the attention of the researchers due to these benefits
Can form a large-scale networks
Can process complex protocols
Minimises the volume of wireless communication required to perform tasks by distributed or local precipitations
Processes the complicated power saving modes of operation in respect to the conditions and the state of the network
Mobile Ad hoc Network (MANET), is a combination of the dynamic network mobile devices connected by various links. Works on the comparatively limited bandwidth. The network topologies are dynamic and vary from time to time. Each mobile device in a network must co-operate with each other device for transferring traffic. This network operates self or can incorporate into LAN. The MANET further classified into three types.
Vehicular Ad hoc Networks (VANETs)
Intelligent Vehicular Ad hoc Networks (InVANETs)
Internet Based Mobile Ad hoc Networks (iMANET)
Applications of MANET vary from small, static networks that are constrained by the power sources to large scale portable and active networks.
http://airccse.org/journal/graphhoc/papers/0310jgraph7.pdf
Technologies used for Ad Hoc Networks
The technologies that are used in the mobile ad hoc networks are
There are two standards that are used in the ad hoc networks they are the IEEE 802.11 and Bluetooth specifications for WLANs and short-range wireless communications respectively [3].
Multi-hop networks which covers a large number of square kilometres can be possible to built using IEEE 802.11
The ad hoc wireless body and PAN s are built by using the Bluetooth technology
The performance of these technologies are measured using indices like the through put and the delay
Throughput: It is defined as the highest fraction of the channel bandwidth utilised by the successfully transmitted messages
Delay: Delay is of several types like access delay; broadcast delay and queuing delay based on the time instants are considered and measured.
The Applications of MANET
The advancements and the flexibility MANET has provided for the wireless communication resulting to diverse applications. This network can be used anywhere irrespective of the availability of the communication infrastructure. The mobile hosts in the ad hoc network were allowed to maintain the connections with in the network and also to add and remove from the network easily. The application of the MANET ranges from large scale, mobile, highly dynamic networks to the small static networks which are controlled by the power sources. With the conventional applications that move from the conventional infrastructured environment into the ad hoc network context there are plenty of new applications for the new environment. The applications are like
Emergency services: MANET is useful in the emergency cases like the search and rescue operations, the disaster recovery and the medical needs such as the retrieval of patient's record at the point of contact and when the infrastructure is lost due to catastrophic disaster [2].
Tactical networks used for the battlefield operations and for the military communications
Commercial environments (electronic commerce) such as accessing the customer records from the field, make and receive the payments from anywhere and the vehicular access of road conditions, weather or local news
Sensor Networks: The real time data of daily functions like weather forecasting, earth activities can be collected using the embedded sensor devices
Educational and business applications such as the virtual classrooms and the business conference rooms
Home and Enterprise Networking like PAN (Personal Area Network) and PDA
Entertainment for example the robotic pets, multi user games and the outdoor internet access
Location aware services like advertising the précised location services, service availability information, precise location travel guides, call forwarding and the transmission of the real workspace to the current location.
ISSUES ASSOCIATED WITH MANET:
MANETs are constructed dynamically by an autonomous system of mobile nodes connected through the wireless links without using the centralised control. As the nodes in the network move randomly and organises themselves arbitrarily. This is responsible for the rapid and unpredictable changes in the network topology. The mobile ad hoc network communicates and organises without having a centralised operator as base station uses the multi hops to route between the nodes. Such networks are called as multi hop wireless ad hoc networks. Every node communicates with the other node which is in its range and uses the other node as the intermediate node to relay messages hop-by-hop with a node that is out of its transmission range. With the flexibility and the convenience offered by the MANETs, it has inherited the issues associated with the conventional wireless networking. They are
The channel is not protected from the outdoor signals
Wired medium is more reliable than the wireless network
The wireless medium does not have readily observable boundaries outdoor where the stations are not able to receive network frames
The channel has time varying and asymmetric properties
There are cases like hidden terminal and exposed terminal may occur
In addition to the above issues, there are many more issues exists in MANETs with the absence of pre-existing setup, Multihop nature, and design complications, etc.
Design complexities and constraints in MANET
Due to the design complications in the mobile ad hoc network such as the lack of the network infrastructure in some cases can be greatly useful but in some other cases it arises some issues. Some of them are as follows
Physical layer limitation
Limited link bandwidth and the quality
Distributed management with the infrastructure less network
Rapid and unpredictable changes in the topology
Difference in node abilities
Energy considerations
Network security
Network reliability
Network scalability
Quality of service
MANET Management
With the multi hop nature of MANET, each device must take the responsibility of carrying the routing packets from source to the destination. So each node of the network shares the management of the network. With the variable behaviour of the nodes in the network the nodes which wants to send the information to the node outside its transmission range using an intermediate node can fail to send its information if the intermediate node fails to send the information or due to any other cause. Due to this distributed design, it is extremely difficult to investigate the fault node.
MANET Topology:
With every move of the mobile host in the network the topology changes. This change results in the changes in route which leads to the partitions in the network and in most cases some packet losses
MANET Physical Layer
The contained wireless range and mutual frequency range leads to specific mobile ad hoc problems like
Collisions Risk and the packet losses
Hidden terminal problems
Exposed terminal problems
Collision Risk and Packet Loss:
A
C
Blaptop_04 laptop_04
laptop_04
In the above example both the nodes A and B tries to communicate with the node C at the same time. But the traffic at the node C collides and both the packet are lost at the node C.
Hidden Terminal:
Exposed Terminal:
MANET Bandwidth Constraints:
The bandwidths that are used by MANETs have a large number of capacity levels
The bandwidth used in the wireless network is more error-prone and more insecure than the bandwidths used in the wired connections
These aspects lead to lower capacity through put than the capacity of equivalent wired connections
And this lower capacity wireless links results to the higher congestion issues
MANET Node Variability
The mobile hosts in the mobile ad hoc network will have one or more radio interfaces having contrast capabilities. Node radios may sometimes operates in various frequency bands. These node capabilities may result in the asymmetric links. The software and the hardware configurations of the mobile host can affect the processing capabilities
MANET Energy Limitations:
The batteries that are used by the individual node in the network limit the processing power that minimises the services and applications supported by each node. The node acting both as the end user and sometimes as a router is becoming a major problem in MANETs as there is a need of additional energy to forward the packets from other nodes.
Link distance:
i) The link distance must be controlled by topology management.
ii) The main aim of it is to minimise the total network power used to the smallest extent possible by assigning the transmit power levels to nodes individually
Routing protocols: Routing protocols are responsible to reduce the power required for the transmission of packets between the nodes by minimising the routing paths.
The ability of the network mainly relies on the transmit power levels so as to control the congestion. Also the hidden terminal problems arises due to the energy limitations
MANET Reliability:
Reliability relies on routing and forwarding the packets but with the problems in the network like the network overload, the broken connections between the nodes and with the misbehaving nodes affecting the reliability of the network as a whole. As there is no centralised management to look after these faults it is very difficult to find them and isolate from the network. Thus the reliability must depend on the properly designed protocols.
MANET security:
Generally the mobile networks are not secure physically as they move randomly and with the distributed management in the network the security of the entire network totally relies on the security of the individual node.
There are some security issues with the lack of maintaining the security considerations like
Lack of confidentiality on the network results to the wireless eavesdropping
The protection of wireless infrastructure depends on the access control
Lack of Data Integrity leads to the tampering of traffic
And finally the Denial Of Service
Wireless Eavesdropping:
Any radio receiver with the signals that are compatible to the signals used by the targeted Ad hoc network can result to the wireless eavesdropping. It is explained pictorially as shown in the figure below.
A
B
C
MANET scalability:
Scalability plays an important role in the effective deployment of a MANET. The most of the management algorithms that are available in the market were made for the small networks whereas the MANET applications include large networks with thousands of nodes. The factors that influence the scalability of a MANET are Addressing, Routing, Location Management, Configuration Management, Interoperability, security and the high capacity wireless technologies.
MANET Quality of Service:
Quality of Service is very important for a network and it is very difficult to maintain the Quality of Service in MANETs this is due to the large networks consists of nodes having limited resources
ANALYSIS
There are five important security services for MANETs. They are Confidentiality, Integrity, Authentication, Availability and Non-repudiation.
Authentication is important of all the five security services though other services are important. Because it is important for a node to know to which node it is actually communicating as it is worthless to protect data from being exposed without knowing it. Thus it is a very important service for a secured system. Once the authentication is achieved then it is a matter of encrypting the data using the key agreed by the respective nodes.
The work related to the ad hoc network security is classified into 3 categories. They are
Providing basic security Infrastructure: As there is no basic infrastructure for MANET so obviously there will be no trust infrastructure like PKI to all the nodes of a network. First the basic infrastructure is to be established and then the security associations between the communicating nodes must be established.
Secure Routing: every node of a MANET involves in routing activities. The routing information is to be exchanged to keep the network connected and then should ensure the secure data packet forwarding.
Misbehaviour or Intrusion detection and response: As the nodes participated in MANET are wireless and can move rapidly makes it exposed to intrusions and misbehaviours which is not seen in the wired medium.
The security architecture for MANETs is designed at five stages
End-to-End Security
Network Security
Routing Security
Communication Security
Trust Infrastructure
End-to-End Security Layer: It refers to the end system security like SSL, SSH and any application-specific security protocol. As the security mechanisms are restricted to the anticipated nodes the security protocol in this layer doesn't depend on the underlying networking technology. Any service that is provided in this layer depends on the security needs of the specific application.
Network security layer: It refers to the security mechanisms of the network protocols that are used for the sub-network access operations in between the end systems. For instance the security services can be achieved such as end point authentication, confidentiality and integrity as the network layer security protocol IPSec provides.
Routing Security Layer: This layer refers to the security mechanisms that are used by the routing protocols. In MANET, nodes share the information of neighbourhood connectivity to construct a view of the network topology in a way to route the data packets to the endpoints. Routing security layer is very important as every node in the network participated involves in the routing activity which is crucial to keep the network connected. This layer involves two responsibilities. One among them is to secure routing, in which the nodes has to share the routing information to stay connected in the network. And the second responsibility is secure data forwarding aspect, in which data packets must be protected from altering, dropping and tampering.
Communication security: This layer refers to the security mechanisms applied to the node to node transmission of data frames like WEP which is used in the data link layer of OSI model. This layer is responsible to protect the data frame from eavesdropping, interception.
Trust Infrastructure Layer:
Security Architecture used in the military applications:
The security requirements for the military applications are stringent than in a MANET of any industrial application. Both the information security and routing topology requirements are higher in a military scenario. The functionalities that were designed from each layer for the military application are as follows.
Data is protected in a most granular manner in the application layer therefore the best method to secure data in respect to their different requirement at end-to-end security layer. For instance managing data confidentiality and integrity is more important at the end-to-end point layer. This is because it is easy to defend here from alteration, fabrication or compromise. And it is very crucial in the military operations where the planned and calculated information is sent.
Hence it is not possible to organize a centralised firewall or security gateway in an ad hoc network. It becomes difficult for the centralised gateway to provide the network access control for all the mobile nodes. Thus the nodes themselves will take care of the network access control and IP data packet protection. There is need to find the means to protect the data packet as it is not possible to use IPSec protocol for the mobile scenario. The underlying routing protocol that supports the multi-path routing mechanisms from [4] works at the network layer uses the advantage of multi route between the communicating routes to attain reliability and maximises the confidentiality in transmitting the data packets using the route from source node to destination node.
The network topology must be kept confidential in the military operations and also the traffic analysis must not be analysed in the routing security layer. The protocol designers must try to design the routing protocols in a way to hide the network topology from outsiders and also to protect from the attacks anticipated at the routing level like the false routing updates, denial of service so that the confidentiality and integrity can be provided at this layer.
The communications in the military applications must be kept secret and this requirement is effectively fulfilled at the communication layer. Like by using the spread spectrum technologies makes it hard to capture the signals or using the antennas to impact the signal power in space. 802.11and WEP are useful in controlling the link access.
It appears to be common to anticipate a PKI based on the centralised operator to pre-establish the trust relationship for all the nodes because of the alike hierarchical relationships between the nodes and this is in fact not possible due to the reason that this cannot be managed in the compromised case. But there is one trust model for the military operation. One such model is Resurrecting Duckling Security Model, in which the technique called master-slave is used for the secure transmission between the nodes. The secrecy in this technique is maintained as the master and slave shares the common secret but the security association is only organised by slave. The security requirements for the commercial purposes are a bit easier than in the military applications so the trust infrastructure can be obtained using the PGP-like model or the location limited channel model.
http://www.cn.apan.net/cairns/NRW/43-Yu%20Shuyao.pdf
