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 organise themselves arbitrarily; thus, the network's wireless topology may change rapidly and unpredictably. Such a network may operate in a standalone fashion, or may be connected to the larger Internet.
The earliest MANETs were called "packet radio" networks, and were sponsored by DARPA in the early 1970s. BBN and SRI designed, built, and experimented with these earliest systems. Experimenters included Jerry Burchfiel, Robert Kahn, and Ray Tomlinson of later TENEX, Internet and email fame. It is interesting to note that these early packet radio systems predated the Internet, and indeed were part of the motivation of the original Internet Protocol suite. Later DARPA experiments included the Survivable Radio Network (SURAN) project, which took place in the 1980s. Another third wave of academic activity started in the mid 1990s with the advent of inexpensive 802.11 radio cards for personal computers. Current MANETs are designed primarly for military utility; examples include JTRS and NTDR.
The popular IEEE 802.11 ("Wi-Fi") wireless protocol incorporates an ad-hoc networking system when no wireless access points are present, although it would be considered a very low-grade ad-hoc protocol by specialists in the field. The IEEE 802.11 system only handles traffic within a local "cloud" of wireless devices. Each node transmits and receives data, but does not route anything between the network's systems. However, higher-level protocols can be used to aggregate various IEEE 802.11 ad-hoc networks into MANETs.
A list of some ad-hoc network protocols can be found in the Ad hoc protocol list.
See also
External links
References
Packet Radio Papers
- J. Burchfiel, R. Tomlinson, M. Beeler, "Functions and structure of a packet radio station", AFIPS 1975, p. 245.
- Kahn, R. E., "The Organization of Computer Resources into a Packet Radio Network," IEEE Transactions on Communications, Vol. COM-25, No. 1, pp. 169-178 (January 1977).
- Kahn, R. E., Gronemeyer, S. A., Burchfiel, J., Kunzelman, R. C., (1973) "Advances in Packet Radio Technology", Proceedings of IEEE. vol. (11):1468--1496, November 1978.
- Jubin, J., and Tornow, J. D., "The DARPA Packet Radio Network Protocols", Proceedings of the IEEE, vol 75, no 1, January 1987.
- N. Schacham and J. Westcott, "Future directions in packet radio architectures and protocols", Proceedings of the IEEE, 75(1):83-99, Jan 1987.
Introduction
Local Area Network (LAN) is the technology that connects computers and other devices in a relatively confined small space such as inside a building or computer labs within a campus. LAN makes it possible for these computers and devices send and receive data to each other. Typically, LAN uses "wires" or cables to connect the devices. In modern LANs, twisted-pair cabling has replaced coaxial cable because of it is relatively inexpensive, easier to install and can accommodate faster networking transmission rate.
As the popularity of cellular phones, portable (notebook) computers, Personal Digital Assistant (PDA or palmtop) devices grow in addition to the difficulty or sometimes impossibility of installing LAN cabling in historical buildings or remote sites, the demand for wireless LAN becomes more substantial.
Wireless LAN relies on electromagnetic waves as media through which the signals are transmitted in the atmosphere. These waves are arranged according to their frequencies.
Because the frequencies in the 2.4 to 2.4835 GHz band (also called the "2.4 GHz band") are not regulated by government bodies, they are often used to send and receive signals for the wireless connected devices. Each device in the network is called a node.1
While the twisted-pair or coaxial cables provide fixed guided paths for wire-bound signals, the atmosphere does not allow for such stable paths for wireless signals to follow.
This characteristic calls for setting up complex infrastructure and central administration. MANET is one of the solutions to simplify the routing of wireless transmission.
What is MANET?
A mobile ad-hoc network (MANET) is peer-to-peer connections that are formed automatically and spontaneously between nodes without the need of an infrastructure, centralized controller, or an intervening connectivity device such as an access point. Access point (AP) is a hardware device that acts as a hub for wireless devices to connect to a wired LAN2.
In absence of intervening connectivity device, each node in a MANET logically has a router that may have multiple wireless communication interfaces to other nodes.3
In this peer-to-peer network, each device can communicate directly with every other device without any node acted as authority. In other words, each node can be a data endpoint or intermediate repeater to another node. Because of this collaboration, MANET is also known as mesh network for its physical layout (or topology) of the participating devices resembling a mesh.
MANET’s ad hoc mesh network provides redundant communication links for nodes which result in improved fault tolerance for the network. Transmission flaws of the network caused by interference known as noise. Sources of noise include electromagnetic interference (EMI) which comes from electrical devices or cables carrying electricity or thunderstorm as well as radiowaves. If one path encounters noise, the signals will immediately “hop” to another path.
When a wireless signal follows a straight line from its transmitter to its intended receiver, this ideal propagation path is known as line-of-sight (LOS). LOS gives the clearest possible signal while using the least amount of energy. LOS cannot be achieved because the atmosphere, the medium for the wireless transmission, distorts the transmission paths. Furthermore, objects standing in the signal’s way also cause the signal reflect, diffract or scatter. MANET solves the non-LOS issues by allows the signals to traverse from one node to another in the mesh network.
In addition, since signals are attenuated (or become weaker) when they travel further away from their network coverage area, MANET’s mesh networks increase the distance limit imposed by the attenuation of the signals and thus widen the coverage area.
When MANETs are tied to an IP_based networks such as Internet, they are referred to as Hybrid MANETs.
MANET’s challenge lies in the demand of updating the communication routes in its mesh network quickly and accurately as the mobile nodes move unpredictably.
Protocols
On March 23, 1983, United States President Ronald Reagan announced a space-based defensive system, called Strategic Defense Initiative, or "Star Wars", that employed advanced technology to destroy attacking missiles. From then on, research on military applications using wireless transmission has become prevalent.4
In order to provide standardized routing functionality to support this mobile networking infrastructure, the Mobile Ad hoc Networks working group within the Internet Engineering Task Force (IETF) was formed to standardize the protocols and specifications of ad hoc wireless networks.5
Existing MANET protocols include Optimized Link State Routing protocol (OLSR), Ad hoc On-demand Distance Vector Protocol (AODV), and Dynamic Source Routing protocol (DSR).
Optimized Link State Routing protocol (OLSR)
According to the OLSR RFC (3626)6, OLSR is a pro-active, table driven routing protocol for MANETs. It uses a technique called multipoint relaying for message flooding.3 Message flooding refers to a node acting as a bridge by sending a data frame to all nodes other than the node from which the frame is received. Flooding is a technique to make sure a frame will reach its destination by sending it along all possible paths.7
The Optimized Link State Routing Protocol (OLSR) was developed to exchange topology information with other nodes regularly. Each node chooses a group of neighbouring nodes as “Multipoint Relays” (MPR). Only those nodes chosen as MPRs will forward flooding control traffic periodically.
The MPR nodes also declare link state information to their selectors for them to calculate the shortest path to the destinations.
OLSR developed its concept of forwarding and relaying from High Performance Radio Local Area Network (HIPERLAN), a MAC layer protocol developed by the European Telecommunications Standards Institute.
Ad hoc On-demand Distance Vector Protocol (AODV)
AODV protocol is both an on-demand and a table driven protocol. It is called a reactive protocol because it starts routing only on demand.
The packet size in AODV is the same and there is no need to broadcast to the whole system when a location change occurs. Each route has a lifetime and is maintained only if it is in active communication. AODV maintains only one route per a source-destination nodes pair.
Because AODV creates route on-demand, it scales well in MANET. This feature makes it the easiest and most supported MANET protocol.8
According to the IETF’s RFC (3561)9, AODV determines unicast routes from source node to destination node by assigning a destination sequence number to each route entry. It is created by the destination node and together with other routing information, it is sent to the requesting nodes. The requesting node chooses the route with the greatest sequence number.
When the communication links break, AODV notifies the affected nodes so that they can invalidate the broken routes.
Dynamic Source Routing protocol (DSR)
The Dynamic Source Routing protocol (DSR) is also a reactive or on-demand routing protocol. When a source node sends a packet to a destination node, the source node sends packet with the routing information as well as the data to the destination node. This results in different size for each packet. Larger size packets will be fragmented into smaller packets. These smaller packets may arrive the destination in different orders.
DSR is compatible with Mobile IP. Nodes using Mobile IP and DSR can be migrated seamlessly between wireless LANS (WLANs), cellular data services, and DSR mobile ad hoc networks.10
DSR consists of two main mechanisms: Route Discovery and Route Maintenance.
- Route Discovery allows a source node to obtain route information of the destination node before attempting to send a packet to it.
- Route Maintenance provides a mean by which a source node, while actually sending packet to the destination node using the routing information supplied by Route Discovery, can detect if the network topology has changed such that it can not use the routing information any more. If Route Maintenance does detect the route is broken, it will use any other route it knows that can lead to the destination node. If it does not have any valid routing information, it invokes Route Discovery again to find a new route
These two mechanisms operate on-demand, thus making the routing packet overhead scale automatically. They can also be used in load-balancing the network traffic.
DSR is an efficient routing protocol in that it does not require nodes within the network send periodic routing advertisement, link status information, or detect neighbouring nodes to each other.11
Commercial application
Bluetooth
Bluetooth was first conceived as a short-range, low-power, low-complexity, and inexpensive radio interface by Ericsson. Later, a Special Interest Group (SIG) formed by major computer and telecommunication vendors such as 3Com, Ericsson, IBM, Intel, Lucent, Microsoft, Motorola, Nokia, and Toshiba took over the project with the objective of connecting heterogeneous devices.
Bluetooth is regarded as the first commercial application of ad hoc wireless networking. It standardizes the single-hop wireless link and groups nodes in smaller geographical area where each node can communicate with any other nodes.5
The group of nodes Bluetooth forms is called piconets. A collection of piconets is called scatternet. Scatternet uses DSR multi-hop routing protocols.
NovaRoam’s EH900TM Mobile Router
NovaRoam claims that its EH900 operates in the license-free 902-928 MHz band, and is capable of closing stationary point-to-point links up to 25 miles with proper installation and line of sight.
EH900 employs AODV protocol so the network control is decentralized. Every network participant can act as a repeater when direct, one-hop routes are unavailable. Therefore it avoids the formation of a single point of failure in the network.
NovaRoam’s EH900 can be used as long-range industrial applications, such as water/wastewater monitoring, oil & gas field monitoring.12
Military application
MANET’s self-organizing, mobile networking infrastructures offer advantages not only for commercial applications but also for military applications.13&sup
NovaRoam TD250TM Mobile Router
NovaRoam’s TD250 can act as an intelligent repeater where range or terrain prevent direct radio links between a field site and base. This capability extends the range of the network with line-of-sight radio links. NovaRoam claims that the effective range of 70 miles can be setup by a TD250 router.
Data confidentiality and integrity is secured with 128-bit key length AES (Advanced Encryption Standard) encryption.
With waterproof external interfaces including an Ethernet port, serial port, antenna connection, and power input jack as well as its filtering and internal amplifier design, NovaRoam’s TD250 is trying hard to overcomes environmental interference.14
OPNET Modeling Terrain Effects
OPNET developed software model that simulates MANETs and offers off-the-shelf models of MANET protocols such as DSR, AODV, and OLSR.15
OPNET’s routing protocol models integrates with the IP and Wireless LAN models. It also hosts the MANET Model Development Consortium with over 150 members from government, industry, and academia.16
Conclusion
According to Patrick Mannion, EE Times, Wireless mesh networks are potentially more robust than centralized network architectures such as Wi-Fi.17
The IETF working group on mobile ad hoc networks (MANET) has been developing routing protocols optimized for different conditions. Reactive protocols, such as AODV and DSR, start route only on demand. This saves overhead while incurs delay in discovery routes. Proactive protocols, such as OLSR creates lot of overhead by trying to establish all routes within the network before a packet is sent. The advantage is when a route is needed, the route is already known and can be immediately used.3
Various application and experiments are being carried out to take advantage of the robustness of MANET’ decentralized, self-organizing, and self governing mesh network. The potential of its usage is vast when mobile devices become more popular and available.
References
1 Dean, Tamara. Network+ Guide to Networks. 3d Ed. Thomson Course Technology. 2004. pp 123, 127
2 Mobile Ad hoc Network Technology. NovaRoam Mobile Router. 16 March 2005
http://www.novaroam.com/Inside.asp?n=Technology&p=MANET
3 Ad-hoc and OLSR.
http://www.olsr.org/
4 Cold War Chronology.
http://www1.cnn.com/SPECIALS/cold.war/kbank/
5 Murthy, C. Siva Ram and Manoj, B. S. Ad Hoc Wireless Networks Architectures and Protocols. May 24, 2004
http://safari.informit.com/?XmlId=013147023X
6 Request for Comments: 3626. T. Clausen, Ed. P. Jacquet, Ed. October 2003
http://ietf.org/rfc/rfc3626.txt
7 Stamper, David A. and Case, Thomas. Business Data Communications. 6th Ed. Prentice Hall. New Jersey. 2003pp 605
8 AODVjr, AODV Simplified. Chakeres, Ian D. and Klein-Berndt, Luke. Mobile Computing and Communications Review, Volume 6, Number 3
http://portal.acm.org/ft_gateway.cfm?id=581309&type=pdf
9 Request for Comments: 3561. Perkins, C. and Belding-Royer, E. July 2003
http://www.ietf.org/rfc/rfc3561.txt
10 The Dynamic Source Routing Protocol. Maltz, David A. July 23, 2003.
http://www-2.cs.cmu.edu/~dmaltz/dsr.html
11 INTERNET-DRAFT. IETF MANET Working Group. Johnson, David B., Maltz, David A. and Hu, Yih-Chun. 19 July, 2004.
http://www.ietf.org/internet-drafts/draft-ietf-manet-dsr-10.txt
12 NovaRoam EH900TM Mobile Router. Nova Engineering, Inc. March 16, 2005.
http://www.novaroam.com/Inside.asp?n=Solutions&p=NR-EH900
13 Internet-Based Mobile Ad Hoc Networking. IEEE Internet Computing Online.
http://csdl.computer.org/comp/mags/ic/1999/04/w4063abs.htm
14 NovaRoam TD250TM Mobile Router Nova Engineering, Inc. 16 March 2005
http://www.novaroam.com/Inside.asp?n=Solutions&p=NR-TD250
15 Military applications. Federal Computer Week. Moore , John. Aug. 25, 2003
http://www.fcw.com/supplements/homeland/2003/sup3/hom-manet2-08-25-03.asp
16 MANET Discrete Event Simulation
http://www.opnet.com/products/library/MANET.html
17 Patrick Mannion, EE Times Mobile Pipeline. November 17, 2003
http://www.mobilepipeline.com/showArticle.jhtml?articleID=16100881
Last updated: 08-20-2005 01:52:37
