Wireless mesh network - AbsoluteAstronomy.com

A wireless mesh network (WMN) is a communications network

Telecommunications network

A telecommunications network is a collection of terminals, links and nodes which connect together to enable telecommunication between users of the terminals. Networks may use circuit switching or message switching. Each terminal in the network must have a unique address so messages or connections...

made up of radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

nodes

Node (networking)

In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...

organized in a mesh

Mesh networking

Mesh networking is a type of networking where each node must not only capture and disseminate its own data, but also serve as a relay for other nodes, that is, it must collaborate to propagate the data in the network....

topology

Network topology

Network topology is the layout pattern of interconnections of the various elements of a computer or biological network....

. Wireless mesh networks often consist of mesh clients, mesh routers and gateways.The mesh clients are often laptops, cell phones and other wireless devices while the mesh routers forward traffic to and from the gateways which may but need not connect to the Internet. The coverage area of the radio nodes working as a single network is sometimes called a mesh cloud. Access to this mesh cloud is dependent on the radio nodes working in harmony with each other to create a radio network. A mesh network is reliable and offers redundancy. When one node can no longer operate, the rest of the nodes can still communicate with each other, directly or through one or more intermediate nodes. The animation below illustrates how wireless mesh networks can self form and self heal. Wireless mesh networks can be implemented with various wireless technology including 802.11, 802.15, 802.16, cellular technologies or combinations of more than one type.

A wireless mesh network can be seen as a special type of wireless ad-hoc network

Wireless ad-hoc network

A wireless ad-hoc network is a decentralized type of wireless network. The network is ad hoc because it does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed wireless networks...

. A wireless mesh network often has a more planned configuration, and may be deployed to provide dynamic and cost effective connectivity over a certain geographic area. An ad-hoc network, on the other hand, is formed ad hoc

Ad hoc

Ad hoc is a Latin phrase meaning "for this". It generally signifies a solution designed for a specific problem or task, non-generalizable, and not intended to be able to be adapted to other purposes. Compare A priori....

when wireless devices come within communication range of each other.
The mesh routers may be mobile, and be moved according to specific demands arising in the network. Often the mesh routers are not limited in terms of resources compared to other nodes in the network and thus can be exploited to perform more resource intensive functions. In this way, the wireless mesh network differs from an ad-hoc network, since these nodes are often constrained by resources.

Architecture

Wireless mesh architecture is a first step towards providing cost effective and dynamic high-bandwidth networks over a specific coverage area. Wireless mesh architectures infrastructure is, in effect, a router network minus the cabling between nodes. It's built of peer radio devices that don't have to be cabled to a wired port like traditional WLAN access points (AP) do. Mesh architecture sustains signal strength by breaking long distances into a series of shorter hops. Intermediate nodes not only boost the signal, but cooperatively make forwarding decisions based on their knowledge of the network, i.e. perform routing. Such an architecture may with careful design provide high bandwidth, spectral efficiency, and economic advantage over the coverage area.

Wireless mesh networks have a relatively stable topology except for the occasional failure of nodes or addition of new nodes. The path of traffic, being aggregated from a large number of end users, changes infrequently. Practically all the traffic in an infrastructure mesh network is either forwarded to or from a gateway, while in ad hoc networks or client mesh networks the traffic flows between arbitrary pairs of nodes.

Management

This type of infrastructure can be decentralized (with no central server) or centrally managed (with a central server), both are relatively inexpensive, and very reliable and resilient, as each node

Node (networking)

In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...

needs only transmit as far as the next node. Nodes act as routers to transmit data from nearby nodes to peers

Peer-to-peer

Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...

that are too far away to reach in a single hop, resulting in a network that can span larger distances. The topology of a mesh network is also reliable, as each node is connected to several other nodes. If one node drops out of the network, due to hardware failure or any other reason, its neighbors can quickly find another route using a routing protocol.

Applications

Mesh networks may involve either fixed or mobile devices. The solutions are as diverse as communication needs, for example in difficult environments such as emergency situations, tunnels, oil rigs, battlefield surveillance, high speed mobile video applications on board public transport or real time racing car telemetry. An important possible application for wireless mesh networks is VoIP. By using a Quality of Service scheme, the wireless mesh may support local telephone calls to be routed through the mesh.

Some current applications:

U.S. military forces are now using wireless mesh networking
Mesh networking
Mesh networking is a type of networking where each node must not only capture and disseminate its own data, but also serve as a relay for other nodes, that is, it must collaborate to propagate the data in the network....

to connect their computers, mainly ruggedized laptops, in field operations.
Electric meters now being deployed on residences transfer their readings from one to another and eventually to the central office for billing without the need for human meter readers or the need to connect the meters with cables.
The laptops in the one laptop per child program use wireless mesh networking to enable students to exchange files and get on the Internet even though they lack wired or cell phone or other physical connections in their area.
The 66-satellite Iridium constellation
Iridium satellite constellation
The Iridium satellite constellation is a large group of satellites providing voice and data coverage to satellite phones, pagers and integrated transceivers over Earth's entire surface. Iridium Communications Inc...

operates as a mesh network, with wireless links between adjacent satellites. Calls between two satellite phones are routed through the mesh, from one satellite to another across the constellation, without having to go through an earth station
Earth station
A ground station, earth station, or earth terminal is a terrestrial terminal station designed for extraplanetary telecommunication with spacecraft, and/or reception of radio waves from an astronomical radio source. Ground stations are located either on the surface of the Earth, or within Earth's...

. This makes for a smaller travel distance for the signal, reducing latency, and also allows for the constellation to operate with far fewer earth stations that would be required for 66 traditional communications satellites.
The Commotion Wireless Project proposes building a 'device-as-infrastrucure' distribution crypted communications platform

Operation

The principle is similar to the way packets travel around the wired Internet

Internet

The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...

— data will hop from one device to another until it reaches its destination. Dynamic routing

Routing

Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...

algorithms implemented in each device allow this to happen. To implement such dynamic routing protocols, each device needs to communicate routing information to other devices in the network. Each device then determines what to do with the data it receives — either pass it on to the next device or keep it, depending on the protocol. The routing algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

used should attempt to always ensure that the data takes the most appropriate (fastest) route to its destination.

Multi-radio mesh

Multi-radio mesh refers to a unique pair of dedicated radios on each end of the link. This means there is a unique frequency used for each wireless hop and thus a dedicated CSMA

Carrier Sense Multiple Access

Carrier Sense Multiple Access is a probabilistic Media Access Control protocol in which a node verifies the absence of other traffic before transmitting on a shared transmission medium, such as an electrical bus, or a band of the electromagnetic spectrum."Carrier Sense" describes the fact that a...

collision domain

Collision domain

A collision domain is a section of a network where data packets can collide with one another when being sent on a shared medium or through repeaters, in particular, when using early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network...

. This is a true mesh link where you can achieve maximum performance without bandwidth degradation in the mesh and without adding latency. Thus voice and video applications work just as they would on a wired Ethernet network. In true 802.11 networks, there is no concept of a mesh. There are only Access Points (AP's) and Stations. A multi-radio wireless mesh node will dedicate one of the radios to act as a station, and connect to a neighbor node AP radio.

Research topics

One of the more often cited papers on Wireless Mesh Networks identified the following areas as open research problems in 2005 -

New modulation scheme
- In order to achieve higher transmission rate, new wideband transmission schemes other than OFDM
  Orthogonal frequency-division multiplexing
  Orthogonal frequency-division multiplexing is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio...
  
  and UWB
  Ultra-wideband
  Ultra-wideband is a radio technology that can be used at very low energy levels for short-range high-bandwidth communications by using a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging...
  
  are needed.

Advanced antenna processing
- Advanced antenna processing including directional
  Directional antenna
  A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....
  
  , smart
  Smart antenna
  Smart antennas are antenna arrays with smart signal processing algorithms used to identify spatial signal signature such as the direction of arrival of the signal, and use it to calculate beamforming vectors, to track and locate the antenna beam on the mobile/target...
  
  and multiple antenna technologies is further investigated, since their complexity and cost are still too high for wide commercialization.

Flexible spectrum management
Spectrum management
Spectrum management is the process of regulating the use of radio frequencies to promote efficient use and gain a net social benefit.The term radio spectrum typically refers to the full frequency range from 3 kHz to 300 GHz that may be used for wireless communication...
- Tremendous efforts on research of frequency-agile techniques are being performed for increased efficiency.

Cross-layer design
- Cross-layer research is a popular current research topic where information is shared between different communications layers in order to increase the knowledge and current state of the network. This could enable new and more efficient protocols to be developed. A joint protocol which combines various design problems like routing, scheduling, channel assignment etc. can achieve higher performance since it is proven that these problems are strongly co-related. It is important to note that careless cross-layer design could lead to code which is difficult to maintain and extend.

Routing protocols

There are more than 70 competing schemes for routing packets across mesh networks. Some of these include:

AODV
Ad-hoc On-demand Distance Vector
Ad hoc On-Demand Distance Vector Routing is a routing protocol for mobile ad hoc networks and other wireless ad-hoc networks. It is jointly developed in Nokia Research Center, University of California, Santa Barbara and University of Cincinnati by C. Perkins, E. Belding-Royer and S...

(Ad hoc On-Demand Distance Vector)
B.A.T.M.A.N.
B.A.T.M.A.N.
The Better Approach To Mobile Adhoc Networking, or B.A.T.M.A.N., is a routing protocol which is currently under development by the “Freifunk”-Community and intended to replace OLSR....

(Better Approach To Mobile Adhoc Networking)
Babel (protocol)
Babel (protocol)
The Babel routing protocol is a distance-vector routing protocol for Internet Protocol packet-switched networks that is designed to be robust and efficient on both wireless mesh networks and wired networks....

(a distance-vector routing protocol for IPv6 and IPv4 with fast convergence properties)
DNVR (Dynamic NIx-Vector Routing)
DSDV (Destination-Sequenced Distance-Vector Routing)
DSR
Dynamic Source Routing
'Dynamic Source Routing' 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...

(Dynamic Source Routing)
HSLS
Hazy Sighted Link State Routing Protocol
The Hazy-Sighted Link State Routing Protocol is a wireless mesh network routing protocol being developed by the CUWiN Foundation. This is an algorithm allowing computers communicating via digital radio in a mesh network to forward messages to computers that are out of reach of direct radio contact...

(Hazy-Sighted Link State)
IWMP
Infrastructure Wireless Mesh Protocol
Infrastructure Wireless Mesh Protocol is based on IWMRA an architecture for building routing protocols for Mesh Networks the main goal of IWMP is to use the fixed MR infrastructure to reduce the routing overhead, deal differently with Mobile and Static nodes and give low delay to obtain routes....

(Infrastructure Wireless Mesh Protocol) for Infrastructure Mesh Networks by GRECO UFPB-Brazil
OLSR
Optimized link state routing protocol
The Optimized Link State Routing Protocol is an IP routing protocol optimized for mobile ad-hoc networks, which can also be used on other wireless ad-hoc networks. OLSR is a proactive link-state routing protocol, which uses hello and topology control messages to discover and then disseminate...

(Optimized Link State Routing protocol)
OORP
Order One Network Protocol
The OrderOne MANET Routing Protocol is an algorithm for computers communicating by digital radio in a mesh network to find each other, and send messages to each other along a reasonably efficient path. It was designed for, and promoted as working with wireless mesh networks.OON's designers say it...

(OrderOne Routing Protocol) (OrderOne Networks Routing Protocol)
OSPF
Open Shortest Path First
Open Shortest Path First is an adaptive routing protocol for Internet Protocol networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system . It is defined as OSPF Version 2 in RFC 2328 for IPv4...

(Open Shortest Path First Routing)
PWRP (Predictive Wireless Routing Protocol)
TORA
Temporally-ordered routing algorithm
The Temporally-Ordered Routing Algorithm is an algorithm for routing data across Wireless Mesh Networks or Mobile ad-hoc networks.It was developed by Vincent Park at the University of Maryland and the Naval Research Laboratory...

(Temporally-Ordered Routing Algorithm)

The IEEE is developing a set of standards under the title 802.11s

IEEE 802.11s

IEEE 802.11s is an IEEE 802.11 amendment for mesh networking, defining how wireless devices can interconnect to create a WLAN mesh network, which may be used for static topologies and ad-hoc networks....

to define an architecture and protocol for ESS Mesh Networking

Mesh networking

.

A more thorough list can be found at Ad hoc routing protocol list

Ad hoc routing protocol list

An ad-hoc routing protocol is a convention, or standard, that controls how nodes decide which way to route packets between computing devices in a mobile ad hoc network ....

Autoconfiguration protocols

Standard autoconfiguration protocols, such as DHCP or IPv6 stateless autoconfiguration may be used over mesh networks.

Mesh network specific autoconfiguration protocols include:

Ad-Hoc Configuration Protocol (AHCP)
Proactive Autoconfiguration (Proactive Autoconfiguration Protocol)
Dynamic WMN Configuration Protocol (DWCP)

External links

IET From hotspots to blankets
Ian. F. Akyildiz and Xudong Wang, "A Survey on Wireless Mesh Networks," IEEE Communications Magazine, vol. 43, no. 9, s23-s30, Sept. 2005
Mesh Networks Research Group Projects and tutorials' compilation related to the Wireless Mesh Networks

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