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This report will investigate mobile ad-hoc networks (MANETs) and how they differ from cellular networks, looking into the main application areas of MANETs. The investigation also looks at challenges dealing with MANETs that need to be addressed. Critical reviews of four MANET routing protocols will be produced for Destination Sequenced Distance Vector Routing (DSDV), Ad hoc On Demand Distance Vector (AODV), Zone Routing Protocol (ZRP) and Dynamic Source Routing (DSR). Lastly a look into why wired networking protocols are inadequate for use with MANETs.
MANETs and how they differ from other wireless models.
MANETs are a type of ad-hoc network, which has the ability to always be changing locations by using nodes that communicate over wireless links without the need for any central control and are self-organised. The reason for this is MANETs to work correctly must be able to organise its own parameters on the go and be able to adjust to any changes that might occur in the environment (). MANETs are wireless connections as they have no fixed infrastructure and don't use any physical connections such as cables. So to sum up the definition of MANET, it's a network of mobile routers that self-configure on the go and are connected by wireless links and don't have any fixed central control.
Other wireless models like cellular networks and wireless LAN work similar to MANETs as they both use wireless connections, however both cellular networks and wireless LAN needs fixed terminals to provide service to mobile nodes in order to work correctly, unlike MANETs that use no fixed terminals. Instead each node acts as the fixed terminal and forwards traffic like a router, even if the traffic has nothing to do with its own use.
Main application area of MANETs
The main application area for MANETs has been the military, as MANETs where first being used by the military. The military needed a way to communicate efficiently whilst on the move without the need for a fixed infrastructure that could be targeted by enemies to prevent important communication of tactical information being cut. MANETs have also made it possible for the military to be able to use unmanned aerial vehicles (UAV) in combat zones and as a result they can reduce the risk of casualties while still getting the same results as a manned vehicle. Most of the early research into MANET was carried out by the defence research projects agency (DRPA) in the early 70's. The DRPA needed the multi hop communications of MANET be fast, reliable, cost efficient, and being able to communicate in hostile battlefields and remote terrains, has become very important to the military as we live in volatile times ().
MANETs are also being used in many other important areas such as law enforcement, rescue missions and education as people need to be taught about how MANETs work and how to use them correctly. Recently MANETs have been picked up to be used commercially, like Jini that was developed by Sun. Jini allows users to connect to printers, scanners and lets phones pass data between each other without the need of the fixed infrastructure that controls all mobile phones connectivity. The only thing the devices will need to connect is, to be in range of each other to form the network as they will each become a node and of course have enough battery power. Issues with battery power will be discussed next in challenges of MANETs.
Challenges dealing with MANET's
Security is the most important challenges to MANTs as they are very vulnerable to attacks, as MANETs use wireless open peer to peer this puts them at a greater risk of malicious attacks, than wired networks that are more secure. With MANETs they rely on the nodes being both the routers and the hosts, unlike wired networks that use dedicated routers to forward their information and are much more secure than there wireless counterparts ().
Other challenges MANETs face are high packet loss rates as the ever changing network grows, it can cause delays and jitter on the network as some packets are arriving out of sync. MANETs have no fixed infrastructure, while this is might be a good thing, it can also bring challenges as nodes in MANETs rely on exhaustible power like batteries to be able to function. As a result management of the power becomes very important to ensure the nodes are operational.
Protocols help with trying to deal with some of the challenges that face MANETs and four of the protocols MANETs use will be discussed in the next section.
A critical review of MANETs routing protocols
MANETs like other wired and wireless models need protocols to function correctly and efficiently. Below is a look into four different MANET protocols.
DSDV- Destination Sequenced Distance Vector Routing. When it comes to MANET protocols there are a number of different types that are pro-active, reactive and hybrid. DSDV is pro-active protocol as it ensures every node remembers one or more tables of the whole network topology. The tables get updated frequently to ensure that each nod has the up to date routing information of other nodes on the network.
DSDV needs to have routing information that is current, to do this nodes have to send topology changes back and forth on a regular basis causing the network to have high overhead on it. The plus side to all the topology updates is that the routes will always be up to date and available on request.
DSDV in MANETs also needs to work without the use of fixed infrastructure when exchanging data, trying to avoid routing loops is also important as routes cause unnecessary traffic on the network. To avoid these routing loop problems each entry in the routing table uses even numbers for the path if it's present or if it's not present, it will use an odd number that will be included within the next update ().
AODV- Ad-hoc On Demand Distance Vector is a routing algorithm is used in MANETs. AODV is a reactive protocol better known as on demand that nodes use between each other to create routes. Routes are only kept while they are needed by the source the nodes. AODV is also known as self-starting as it only gets the routing information when needed.
AODV is capable of two different types of routing, the first one is unicast as it sends information to a single receive on a network that is identified by its unique address and multicast routing is when you send information to a group on a network in one transmission.
ZRP - Zone routing protocol is a hybrid protocol and has the advantage of being able to be either a pro-active or re-active routing protocol. The ZRP controls the overhead of protocols that are pro-active like DSDV and reduce latency issues with re-active protocols like AODV.
ZRP makes up a zone and within the zone are nodes that are required to know the topology of the network to function correctly. Nodes will only know about changes to the topology if it's in their zone, so it does not matter how large a network might be, or get, updates are only sent out locally.
Below is an example of how routes are discovered, node 5 using other nodes in its zone that are 1, 2 and 7 will try and discover nod 9. How it's done is each nod checks the periphery to see if nod 9 is in its zone and once the zone is found it will send back the forwarding route to the nod that will be 9-4-1-5 ().
This diagram is to show how routes are discovered in a Zone Routing Protocol (ZRP)
DSR-Dynamic Source Routing works by trying to figure out the source routes by gathering addresses of each node between the source and the destination while discovering routes. The path information that has been gathered along the way is then stored by the nodes that are processing the route discovery packets. All the new paths found will be used to send data and the source routing will work as the route packets will have the address of the each node the packet will need to travel through.
There are some disadvantages to DSR, like if there are over 200 nodes in the MANET then DSR will not be an efficient routing protocol, as its most effective when there is 200 or less nodes, as to many nodes on the network would cause way to much overhead. Another disadvantage is collisions can also occur when flooding the network between the packets being sent about the network ().
Why wired networks routing protocols are not adequate for MANETs.
Wired networks routing protocols are not adequate for MANETs, as they require a physical connection in the form of wires to be able to communicate. Wired networks would be extremely difficult to setup in some situations for MANETs as cable connection from each node in a battlefield, or a disaster zone would not be practical or even possible to setup. MANET routing protocols work towards allowing communication on the move, while wired protocols need you to be at a fixed location at all times to communicate. Wired networks are very expensive as they need cabling for each node, this is reason why wired would never be practical for MANETs. Wired network protocols rely on fixed communication with the use of physical cables that is none mobile; this is a problem as wireless network protocols in MANETs work by allowing on the move communication without the need of physical connection and fixed infrastructure.
The investigation into Mobile Ad-Hoc Network is now completed and throughout the investigation, MANETs has shown that they are very important in a number of key areas. MANETs are very important as they can help save lives in the military, rescue missions and natural disasters. MANETs also function differently to other wireless models, as MANET is the only wireless model that does not require any fixed infrastructure to communicate as the moving nodes act as the infrastructure for routing information across the network.
For MANETs to work they require lots of different types of re-active, pro-active and hybrid protocols to even function. If the protocols were not present or functioning incorrectly then the MANET would not work as intended and could also be open to malicious attacks as protocols of MANETs help address issues of the network.
Overall while MANETs has some challenges to overcome with regards to overhead and some security vulnerabilities, but they still currently work very well in areas like military. Due to the continuing success of MANETs this has opened the door for MANETs to also start appearing commercially as well, so the future looks very bright for this very useful and important network type.