Ad-hoc Network System

 

1. INTRODUCTION

 

 

Definition of an Ad-hoc Network System:

          The term ad-hoc does not refer to a network dependent on the above  mentioned existing infrastructure  (phone lines, mobile phone networks,  the Internet, etc), but  it refers  to a temporary network composed only of mobile terminals  fitted with a relay function. And we consider that this ad-hoc network will provide an effective communication  infrastructure for  information  transfer during major disasters like typhoons  and earthquakes.

 

Why Ad Hoc Networks?

          Setting up of fixed access points and backbone infrastructure is not always viable

·        Infrastructure may not be present in a disaster area or war zone.

·        Self configure

·        Are easy to deploy.

 

          As an example, we imagine  the situation that a serious disaster has occurred in a particular region, consequently, the means of communication in that region, such as mobile phones or the Internet,  are completely down. In such a case, it is assumed that the emergency staff of the police, fire service, ambulance service and even the national Self Defence Forces will rush one  after another to the scene of the disaster. Each vehicle in which they arrive is equipped with a mobile terminal hat composes part of an ad-hoc network.  Each staff member also carries one of these mobile terminals in hand.

 

          At the disaster site, each member of staff fans out to their respective posts, and at that time,  literally, a "temporary network" is formed. In other words,  the mobile terminals of the staff in charge and those of all the other disaster relief staff are linked up and for a given short time, an adaptive network infrastructure that meshes together all the emergency  staff in response to that disaster is formed. This infrastructure  can then support  the exchange of various kinds of information,  commencing with map locations.

 

          In addition, it should be emphasized  here that the mobile terminals not only provide a function for information transmission and reception but also provide a function for information transmission and reception but also provide a function for information relay. That is to say, they play a role  like internet routers namely, they control the flow of data traffic in such a way that information packets  are selected and sent to the proper location. This means that the terminals act like repeaters that relay the information packets flying back and forth about the ad-hoc network from one mobile terminal to the next.

2. MOBILE AD  HOC NETWORK

 

Definition :

          Mobile ad hoc Network is an autonomous  system of mobile nodes connected by wireless links, each node operate as an end system and a router for all other nodes in the network without pre-established infrastructure.

 

          Ad hoc is a latin word, which means "for this or for this only".

 

          A MANET is a collection of wireless nodes that can dynamically form a network to exchange information without using any pre-exiting network infrastructure.  A mobile ad hoc network (MANET) is a self configuring  network of mobile routers (and associated hosts) connected by wireless links – the union of which form  an arbitrary  topology. The routers are free to move randomly and organize themselves arbitrarily, thus, the networks wireless topology may change rapidly and unpredictably.  Such a network may operate in a standalone fashion, or may be connected to the larger internet.  Minimal configuration and quick deployment make ad hoc network suitable for emergency situations like natural or human induced disasters, military conflicts etc.

 

          The people's future living environments are emerging, based upon information resources provided by the connections of various communication network for users. New small devices like Personal Digital Assistants (PDAs), mobile phones, handhelds, and wearable computers enhance information processing and accessing capabilities  with mobility. Moreover, traditional home appliances, e.g.  digital cameras, cooking ovens,  washing machines, refrigerators, vacuum cleaners and thermostats, with computing and communicating powers attached, extend the field to a fully pervasive  computing environment. With this in view, modern technologies should be formed within the new paradigm of pervasive computing,  including new architectures,  standards,  devices, services, tools and protocols.

 

          Mobile networking  is one of the most important technologies supporting pervasive  computing. During the last decade,  advances in both hardware and software techniques  have resulted in mobile hosts and wireless networking common and miscellaneous. Generally there are two distinct approaches for enabling wireless mobile units to communicate with each other.

 

Why Mobile Ad hoc Networks:

·        Ease of deployment.

·        Faster deployment

·        No infrastructure is required.

3. ROUTING AND PROTOCOLS IN MANET

 

 

          Routing decisions are made based on feedback or information extracted from the received signal.  Various protocols  have been recently proposed in the Internet Engineering Task Force (IETF)  for executing routing  in a MANET: Zone Routing Protocols (ZRP) Ad Hoc on Demand Distance Vector (AODC) Routing,  Temporally Ordered Routing  Algorithm (TORA), Dynamic Source Routing (DSR) Protocol, Cluster Based Routing  Protocol (CBRP), Core Extraction Distributed Ad Hoc Routing (CEDAR), On Demand Multicast Routing Protocol (ODMRP), and Optimized Link State Routing Protocol (OLSRP).

·        Reactive Protocols

·        Proactive Protocols

·        Hybrid Protocols

 

Routing Protocols:

Reactive Protocols :

          The protocol finds the route on demand by flooding the network with Route Request packets.

 

·        Determine route if and when needed

·        Source initiates route discovery

Example: DSR (Dynamic Source Reactive)

 

Proactive Protocols :

          These algorithms  maintain fresh lists of destinations and their routes by distributing routing tables in the network periodically.

 

·        Traditional distributed shortest path protocols.

·        Maintain routes between every host pair at all times

·        Based on periodic updates,  high routing overhead

Example:  DSDV (Destination Sequenced Distance Vector)

 

Hybrid Protocols :

·        Adaptive, combination of proactive and reactive

Example: ZRP (Zone Routing Protocol)

 

Routing Protocol using Flooding as Basis :

Flooding:

          Flooding is a very simple and easy  routing algorithm. In this method, every incoming packet is sent out on every outgoing line except the one it arrived on.

 

          The drawback of flooding is generation of duplicate packets. These duplicate packets are infinite and has to be controlled to stop this process.

 

 

 

 

 

·        Sender node S broadcasts  packet p to all its neighbors

·        Each intermediate node receiving P forwards P to its neighbors

·        Packet P reaches destination D provided that D is reachable from sender S

·        Node D does not forward the packet

 

Flooding Examples :

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Advantages:

·        Simplicity

·        May be more efficient  than other protocols  when rate of information transmission is low enough that the overhead  of explicit  route  discovery / maintenance incurred by other protocols  is relatively higher.

·        Potentially higher reliability of data delivery.

·        Because packets may be delivered to the destination on multiple paths.

 

Disadvantages:

·        Potentially, very high overhead

·        Data packets may be delivered to too many nodes who do not need to receive them.

·        In our example, nodes J and K may transmit to

·        Node D simultaneously, resulting in loss of the

·        Packet in this case, destination would not receive the packet at all.

 

Dynamic Source Routing:

          Dynamic Source Routing (DSR) is a routing protocol for wireless mesh networks. It is similar to AODV in that it forms a route on demand  when a transmitting  computer requests one.  However,  it uses sources  routing instead  of relying on the routing table at each intermediate device.

 

          Determining source routes requires accumulating the address of each device between the source and destination during route discovery.  The accumulated path information is cached by nodes  processing the route discovery packets.  The learned  paths are used to route packets. To accomplish source routing, the routed packets contain the address of each device the packets will traverse. This may result in high overhead for long paths or large addresses, like IPv6. To avoid using source routing,  DSR optionally  defines a flow id option that allows  packets to be forwarded on a hop by hop basis.

 

          This protocol is based on source routing whereby all the routing information is maintained  (continually updated) at mobile nodes. It has only 2 major phases which are Route Discovery and Route Maintenance. Route Reply would only be generated if the message has reached the intended destination  node (route record which is initially  contained in Route Request would be inserted into the Route Reply).

 

          To return the Route Reply,  the destination node must have a route to the source node.  If the routes is in the Destination Node's route cache,  the route would be used. Otherwise,  the node will reverse  the route based on the route record in the Route Reply message header (symmetric links). In the event of fatal transmission,  the Route Maintenance Phase  is initiated  whereby the Route Error packets  are generated  at a node.  The erroneous hop will be removed from the node's  route cache,  all routes containing the hop are truncated at that point.  Again, the Route Discovery  Phase is initiated  to determine the most viable route.

 

·        When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery.

·        Source node S floods Route Request (RREQ)

·        Each node appends own identifier when forwarding RREQ

 

Route Discovery in DSR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Route Discovery in DSR:

·        Destination D on receiving the first RREQ sends a Route Reply (RREP)

·        Route Reply is sent on a route obtained by reversing the route appended to RREQ

·        REPP includes the route from S to D on which RREQ was received.

 

 

 

 

 

 

 

 

Route Reply in DSR:

·        Route Reply can be sent by reversing the route in Route Request (RREQ) only if links are guaranteed to be bi-directional.

Ø  To ensure this, RREQ should be forwarded only if it received on a link that is known to be bi-directional.

·        If unindirectional (asymmetric) links are allowed, then RREP may need  a route discovery for S from node D.

Ø  Unless node D already knows a route to nodes S

Ø  If a route discovery is initiated by D for a route to S, then the Route Reply is piggybacked on the Route Request from D.

 

Dynamic Source Routing (DSR):

·        Node S on receiving RREP, caches the route included  in the RREP

·        When node S sends a data packet  to D, the entire route is included in the packet header

Ø  Hence the name source routing.

·        Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwarded.

 

Data Delivery in DSR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Advantages:

·         Route maintained only between nodes who need to communicate

·        This reduces overhead of route maintenance

·        Route caching can further reduce route discovery overhead

·        A single route discovery may yield many routes to the destination, due to intermediate nodes replying from local caches.

 

Disadvantages:

·         Packet header length grows with route length due to source routing.

·        Flooding of route request may potentially reach all nodes in the network.

·        Care must be taken to avoid collision between route requests propagated by neighbouring nodes.

·        Insertion of random delays before forwarding RREQ

·        Increased contention is too many route replies come back due to nodes replying using their local cache.

·        Route reply storm problem.

 

4. CHARACTERISTICS OF MANETs

 

 

·        Energy constrained nodes (uses batteries).

·        Bandwidth constrained (wireless links)

·        Dynamic topology leading to frequent and unpredictable changes

·        Broadcast nature of the network

·        Limited security

 

5. APPLICATIONS of MANETs

 

 

·        Metropolitan Area Networks

·        Personal area networking

Ø  Cell phone, laptop, ear phone, wrist watch

·        Military environments

Ø  Soldiers, tanks, planes

·        Civilian environments

Ø  Taxi cab network

Ø  Meeting rooms

Ø  Sports stadiums

Ø  Boats, small air crafts

·        Emergency operations

Ø  Search and rescue

Ø  Policing and fire fighting

 

          With the increase of portable devices as well as progress in wireless communication, ad hoc networking is gaining  importance with the increasing number of widespread applications.  Ad hoc networking can be applied  anywhere where there is little or no communication infrastructure or the existing infrastructure is expensive or inconvenient  to use. Ad hoc networking allows the devices to maintain connections   to the network as well as easily adding and removing devices  to and from the network.  the set of applications for MANETs is diverse,  ranging from large scale,  mobile,  highly dynamic networks, to small, static networks that are constrained by power sources. Besides  the legacy applications that move from traditional  infrastructured  environment into the ad hoc context,  a great deal of new services can and will be generated for the new environment. Typical applications include:

 

1.     Military Battlefield:

Military equipment now routinely contains some sort of computer equipment. Ad hoc networking would allow military to take advantage of commonplace  network technology to maintain an information network between the soldiers,   vehicles, and military information head quarters. The basic techniques of ad hoc network came from this field.

 

2.     Commercial Sector:

Ad hoc can be used in emergency / rescue operations for disaster relief efforts, e.g. in fire, flood or earth quake, emergency rescue operations must take place where non existing  or damaged communications infrastructure  and rapid deployment of a communication network is needed.   Information  is relayed from one rescue team member to another over a small handled.  Other commercial  scenarios include e.g. ship to ship ad hoc mobile communication, law enforcement.

 

3.     Local Level :

Ad hoc network can autonomously link  an instant and temporary multimedia  network using notebook  computer or palmtop computers to spread and share information among participants at e.g.  conference or classroom. Another appropriate local level  application  might  be in home networks where devices can communicate directly to exchange information.  Similarly in other civilian  environments like taxicab,  sports stadium, boat and small air craft.

4.     Personal Area Network (PAN):

Short range MANET can simplify the intercommunication between various mobile devices (such as a PDA, a laptop and a cellular phone). Tedious wired cables are replaced  with wireless connections.  Such an ad hoc network can also extend the access to the internet  or other networks by mechanisms e.g. Wireless LAN (WLAN), GPRS and UMTS. The PAN  is potentially a promising application  field of MANET in the future pervasive computing context. 

 

 

6. Challenges in MANETs

 

 

·        Limited wireless transmission range

·        Broadcast nature of the wireless medium

·        Packet losses due to transmission errors

·        Mobility – induced route changes

·        Mobility – induced packet losses

·        Battery constraints

·        Potentially frequent network partitions

 

7. CONCLUSION

 

 

·        Mobile ad hoc network  is a fourth generation  of networks.

·        Which can turn the dream of getting connected "anywhere and at any time" into reality.

·        As we seen so far designing efficient routing protocols  plays a very important role in ad hoc networks.

 

 

8. REFERENCES

 

Packet Radio Papers:

·        Burchfiel, J., Tomlinson, R., Beeler, M. (1975). "Functions and structure of a packet radio station". AFIPS: 245.

·        Kahn, R. E. (January 1977). "The Organization of Computer Resources into a Packet Radio Network". IEEE Transactions on Communications COM-25 (1): 169–178.

·        Kahn, R. E., Gronemeyer, S. A., Burchfiel, J., Kunzelman, R. C. (November 1978). "Advances in Packet Radio Technology". Proceedings of IEEE 66 (11): 1468–1496.

·        Jubin, J., and Tornow, J. D. (January 1987). "The DARPA Packet Radio Network Protocols". Proceedings of the IEEE 75 (1).

Ad Hoc Network Papers (Overview):

·        Royer, E., Toh, C. (April 1999). "A Review of Current Routing Protocols for Ad-Hoc Mobile Wireless Networks". IEEE Personal Communications 6 (2): 46-55.

·        Mauve, M., Widmer, J., Hartenstein, H. (December 2001). "A Survey on Position-Based Routing in Mobile Ad Hoc Networks". IEEE Network 1 (6): 30-39.

·        Maihöfer, C. (2nd quarter 2004). "A Survey on Geocast Routing Protocols". IEEE Communications Surveys and Tutorials 6 (2).

Ad Hoc Network Books :

·        Ozan, K. Tonguz, Gianluigi Ferrari (May 2006). in John Wiley & Sons.: Ad Hoc Wireless Networks: A Communication-Theoreteic Perspective.