COMPUTER NETWORKING

COMPUTER NETWORKING

Computer networking is the engineering discipline concerned with communication between computer systems or devices. Networking, routers, routing protocols, and networking over the public Internet have their specifications defined in documents called RFCs.[1]Communicating computer systems constitute a computer network and these networks generally involve at least two devices capable of being networked with at least one usually being a computer. The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the Internet[2]). Computer networking is sometimes considered a sub-discipline of telecommunications, and sometimes of computer science, information technology and computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines.A computer network is any set of computers or devices connected to each other. Examples of networks are the Internet, or a small home local area network (LAN) with two computers connected with standard networking cables connecting to a network interface card in each computer. All modern aspects of the Public Switched Telephone Network (PSTN) are computer-controlled, and telephony increasingly runs o

BUSINESS NETWORKING

BUSINESS NETWORKING

A business network can be defined as a group of people that have some kind of commercial relationship. For example the relationships between boss-employee, buyer-supplier, and colleague-colleague.According to experts, business networking functions best when individuals offer to help others to find connections, rather than "cold-calling" on prospects themselves. Business networking can take place outside of traditional business environments. For example, public places such as airports, restaurants, and movie line-ups provide opportunities to make new business contacts if an individual has good social skills.Contents [hide]1 Purpose2 Use of Social Networking Services3 References4 See alsoPurposeOnce a company has assessed its core capabilities it can either flush its assets away or, can find itself in a situation where it cannot compete on attributes, as it doesn't have the necessary resources. Because of this, networks are formed to utilize the advantageous attributes, and the importance here is dependent upon a mutually beneficial relationship that significantly adds to the value of a firm's market offering. With this, there comes a critical responsibility to thoroughly analyze the respective competitors, as there are both significant opportunities and risks associated with network partnerships.Another purpose for a business network is to expand ones knowledge base without extending ones hours for learning and accomplishing new tasks. By utilizing the experiences and knowledge of others within your business network you are able to work more efficiently in the areas of your own expertise. For example, having people with computer related skills, phone skills, psychology background, health background, financial background, legal background, and business can help bring information from each area to the table that each person can share and use to the benefit of their own business.Sharing information and being involved in a group can help your business reach levels you couldn't alone.There are many online networking services that can benefit most businesses, one popular site is Connect Buzz. Yet, there have been an increase in such networking sites that was kicked off by the very popular Linkedin brand and now very clever business networking sites have come into play that not just take into consideration online business networking, which as noted by critics of business networking sites, does not work very well, and combined it with a complicated algorithm that places members of a business network into offline (in real life) networking meetings. One of the pioneers in such a hybrid business networking model is Business Networking Me.Use of Social Networking ServicesAs business is increasingly carried on across the globe, there has become a strong need for business networking to take place on a more virtual level. There are a myriad of social networking tools which have been created to fulfill these needs. Together with software which provides access to on-line meetings and instant messaging, people are able to both access and increase their networks of business professionals without traveling.Social networking is a good way to find people to add to your own business network. People that can benefit from your knowledge and provide you with theirs.Leverage of social media in corporations is an undeniable evolution in our corporate world. No one can ignore the fact that better connected people and better networked companies are more successful. Organizations with deeper alliances and partnerships lead over the ones that work on their own. The goal is to help tea

(Wireless) Ad-hoc networking

Wireless grid

Wireless grids are wireless computer networks consisting of different types of electronic devices with the ability to share their resources with any other device in the network in an ad-hoc manner. A definition of the wireless grid can be given as: "Ad-hoc, distributed resource-sharing networks between heterogeneous wireless devices" The following key characteristics further clarify this concept:

* No centralized control
* Small, low powered devices
* Heterogeneous applications and interfaces
* New types of resources like cameras, GPS trackers and sensors
* Dynamic and unstable users / resources

The technologies that make up the wireless grid can be divided into two main categories; ad-hoc networking and grid computing.

(Wireless) Ad-hoc networking

In traditional networks, both wired and wireless, the connected devices, or nodes, depend on dedicated devices (edge devices) such as routers and/or servers for facilitating the throughput of information from one node to the other. These 'routing nodes' have the ability to determine where information is coming from and where it is supposed to go. They give out names and addresses (IP numbers) to each connected node and regulate the traffic between them. In wireless grids, such dedicated routing devices are not (always) available and the bandwidth that is permanently available to traditional networks has to be either 'borrowed' from an already existing network or publicly accessible bandwidth (open spectrum) has to be used.

A group addressing this problem is MANET (Mobile Ad-Hoc Network).

Advanced Health Checking

Advanced Health Checking

Advanced health checking is the ability of an ADN to determine not only the state of the server on which an application is hosted, but the status of the application it is delivering. Advanced health checking techniques allow the ADC to intelligently determine whether or not the content being returned by the server is correct and should be delivered to the client.

This feature enables other reliability features in the ADN, such as resending a request to a different server if the content returned by the original server is found to be erroneous.

Load Balancing Algorithms

The load balancing algorithms found in today's ADN are far more advanced than the simplistic round-robin and least connections algorithms used in the early 1990s. These algorithms were originally loosely based on operating systems' scheduling algorithms, but have since evolved to factor in conditions peculiar to networking and application environments. It is more accurate to describe today's "load balancing" algorithms as application routing algorithms, as most ADN employ application awareness to determine whether an application is available to respond to a request. This includes the ability of the ADN to determine not only whether the application is available, but whether or not the application can respond to the request within specified parameters, often referred to as an SLA.

Typical industry standard load balancing algorithms available today include:

* Round Robin
* Least Connections
* Fastest Response Time
* Weighted Round Robin
* Weighted Least Connections
* Custom values assigned to individual servers in a pool based on SNMP or other communication mechanism

Application Delivery Network

Application Delivery Network

An Application Delivery Network (ADN) is a suite of technologies that, when deployed together, provide application availability, security, and acceleration. At the core of an ADN is the Application Delivery Controller (ADC), an advanced traffic management device that is often also referred to as a web switch, content switch, or multilayer switch, the purpose of which is to distribute traffic among a number of servers or geographically dislocated sites based on application specific criterion.

The ADN evolved from layer 4-7 switches in the late 1990s when it became apparent that traditional load balancing techniques were not robust enough to handle the increasingly complex mix of application traffic being delivered over a wider variety of network connectivity options.

Application Delivery Techniques

The Internet was designed according to the end-to-end principle [1]. This principle keeps the core network relatively simple and moves the intelligence as much as possible to the network end-points: the hosts and clients. An Application Delivery Network (ADN) enhances the delivery of applications across the Internet by employing a number of techniques designed to optimize the delivery of applications. Many of these techniques are based on established best-practices employed to efficiently route traffic at the network layer including redundancy and load balancing [2]

In theory, an Application Delivery Network (ADN) is closely related to a content delivery network. The difference between the two delivery networks lies in the intelligence of the ADN to understand and optimize applications, usually referred to as application fluency [3].

Application delivery uses one or more layer 4–7 switches, also known as a web switch, content switch, or multilayer switch to intelligently distribute traffic to a pool, also known as a cluster or farm, of servers. The application delivery controller (ADC) is assigned a single virtual IP address (VIP) that represents the pool of servers. Traffic arriving at the ADC is then directed to one of the real web servers based on a number of factors including application specific data values, application transport protocol, availability of servers, current performance metrics, and client-specific parameters. An ADN provides the advantages of load distribution, increase in capacity of servers, improved scalability, security, and increased reliability through application specific health checks.

Increasingly the ADN comprises a redundant pair of ADC on which is integrated a number of different feature sets designed to provide security, availability, reliability, and acceleration functions. In some cases these devices are still separate entities, deployed together as a network of devices through which application traffic is delivered, each providing specific functionality that enhances the delivery of the application.

Application Delivery Network Optimization Techniques

Data Compression and Caching

Data Compression and Caching

ADNs also provide optimization of application data through caching and compression techniques. There are two types of compression used by ADNs today: industry standard HTTP compression and proprietary data reduction algorithms. It is important to note that the cost in CPU cycles to compress data when traversing a LAN can result in a negative performance impact and therefore best practices are to only utilize compression when delivering applications via a WAN or particularly congested high-speed data link.

HTTP compression is asymmetric and transparent to the client. Support for HTTP compression is built into web servers and web browsers. All commercial ADN products currently support HTTP compression.

A second compression technique is achieved through data reduction algorithms. Because these algorithms are proprietary and modify the application traffic, they are symmetric and require a device to reassemble the application traffic before the client can receive it. A separate class of devices known as WAN Optimization Controllers (WOC) provide this functionality, but the technology has been slowly added to the ADN portfolio over the past few years as this class of device continues to become more application aware, providing additional features for specific applications such as CIFS and SAMBA.

Application Delivery Network Reliability & Availability Techniques

Delayed Binding

Delayed Binding

Delayed binding, also called TCP splicing, is the postponement of the connection between the client and the server in order to obtain sufficient information to make a routing decision. Some application switches and routers delay binding the client session to the server until the proper handshakes are complete so as to prevent Denial of Service attacks.

IP Filtering

ADNs often have the ability to filter traffic based on Access Control Lists (ACLs), Bogus IP ranges (Bogon filtering) and deep patcket inspection pattern matching. In some cases, thresholds or rate limiting of IP addresses or ranges of IP addresses may be employed.

Traffic Management

ADNs are increasingly adding advanced traffic management funtionality. The deep packet inspection capabilities of some of these products can identify identify traffic by application type and can be used to analyze, block, shape and prioritize traffic.

Fault Tolerance

Fault Tolerance

The ADN provides fault tolerance at the server level, within pools or farms. This is accomplished by designating specific servers as a 'backup' that is activated automatically by the ADN in the event that the primary server(s) in the pool fail.[13]

The ADN also ensures application availability and reliability through its ability to seamlessly "failover" to a secondary device in the event of a hardware or software failure. This ensures that traffic continues to flow in the event of a failure in one device, thereby providing fault tolerance for the applications. Fault tolerance is implemented in ADNs through either a network or serial based connection.

Network Based Failover

The Virtual IP Address (VIP) is shared between two devices. A heartbeat daemon on the secondary device verifies that the primary device is active. In the event that the heartbeat is lost, the secondary device assumes the shared VIP and begins servicing requests. This process is not immediate, and though most ADN replicate sessions from the primary to the secondary, there is no way to guarantee that sessions initiated during the time it takes for the secondary to assume the VIP and begin managing traffic will be maintained.

Serial Based Failover

In a serial connection based failover configuration two ADN devices communicate via a standard RS232 connection instead of the network, and all sharing of session information and status is exchanged over this connection. Failover is nearly instantaneous, though it suffers from the same constraints regarding sessions initiated while the primary device is failing as network based failover.

Grid Computing

Grid Computing

Grid computing came into existence as a manner of sharing heavy computational loads among multiple computers to be able to compute highly complex mathematical problems (a good real-world example being the SETI@Home project). However, it developed rapidly into a way of sharing virtually any resource that is available on any machine on the grid. Wired grids are now used to share not only computing power, but also hard disk space, data, and applications. The grid topology is highly flexible and easily scalable, allowing users to join and leave the grid without the hassle of time and resource hungry identification procedures, having to adjust their devices or install additional software on them. The goal of grid computing is described as "to provide flexible, secure and coordinated resource sharing among dynamic collections of individuals, institutions and resources" (McKnight, Howison, 2004).
It is intended to be a dynamic network without geographical, political, or cultural boundaries that offers real-time access to heterogeneous resources and still offer the same characteristics of the traditional distributed networks that are in use everywhere in our houses and offices. These characteristics being stability, scalability, and flexibility as the most important ones. Ian Foster offers a checklist for recognizing a grid.

A grid allows:

* Coordination of resources that are not subject to centralized control
* Use of standard, open, general-purpose protocols and interfaces
* Delivery of nontrivial qualities of service

The Wireless Grid

One of the biggest limitations of the wired grid is that users are forced to be in a fixed location as the devices they use are to be hard wired to the grid at all times. This also has a negative influence on the flexibility and scalability of the grid; devices can only join the grid in locations where the possibility exists to physically connect the device to the grid (i.e. there is the need for a hub or a switch to plug into).

One description of the wireless grid is "an augmentation of a wired grid that facilitates the exchange of information and the interaction between heterogeneous wireless devices" (Argawal, Norman & Gupta, 2004)

Argawal, Norman & Gupta (2004) identify three forces that drive the development of the wireless grid:

New user interaction modalities and form factors
Applications that exist on current wired grids need to be adapted to fit the devices used in wireless grids. These devices are usually hand held and therefore the user interface devices (screens, keyboards (if any)) are significantly smaller and availability of additional input devices like a mouse are limited. This means the traditional graphical interfaces found on PCs are not suitable.

Limited computing resources
Wireless devices do not possess the computing power nor the storage capacity of full size devices like a PC or laptop. Therefore wireless applications need to have access to additional computing resources to be able to offer the same functionality that wired networks do.

Additional new supporting infrastructure elements
In the case of an unforeseen event, there will be the need for major amounts of computational and communications bandwidths. An urban catastrophe, for example, would require a dynamic and adaptive wireless network to alert people within the population as well as those in the various coordination and aid services like the police, army, medical services, and government. Applications to provide for these bandwidths and 'instant' networks need to be addressed.

Wireless Grids infrastructure

The infrastructure of the wireless grid consists of three basic levels:

* The physical layer technologies and policies. The physical layer contains the spectrum on which the wireless devices can operate and communicate.
* Network infrastructure
* Middleware to provide communications between heterogeneous devices

HISTORY AND TYPES OF NETWORKS

HISTORY AND TYPES OF NETWORKS

HistoryBefore the advent of computer networks that were based upon some type of telecommunications system, communication between calculation machines and early computers was performed by human users by carrying instructions between them. Many of the social behavior seen in today's Internet was demonstrably present in nineteenth-century telegraph networks, and arguably in even earlier networks using visual signals. [3]In September 1940 George Stibitz used a teletype machine to send instructions for a problem set from his Model K at Dartmouth College in New Hampshire to his Complex Number Calculator in New York and received results back by the same means. Linking output systems like teletypes to computers was an interest at the Advanced Research Projects Agency (ARPA) when, in 1962, J.C.R. Licklider was hired and developed a working group he called the "Intergalactic Network", a precursor to the ARPANet.In 1964, researchers at Dartmouth developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at MIT, a research group supported by General Electric and Bell Labs used a computer (DEC's PDP-8) to route and manage telephone connections.Throughout the 1960s Leonard Kleinrock, Paul Baran and Donald Davies independently conceptualized and developed network systems which used datagrams or packets that could be used in a packet switched network between computer systems.The first widely used PSTN switch that used true computer control was the Western Electric 1ESS switch, introduced in 1965.In 1969 the University of California at Los Angeles, SRI (in Stanford), University of California at Santa Barbara, and the University of Utah were connected as the beginning of the ARPANet network using 50 kbit/s circuits. Commercial services using X.25, an alternative architecture to the TCP/IP suite, were deployed in 1972.Computer networks, and the technologies needed to connect and communicate through and between them, continue to drive computer hardware, software, and peripherals industries. This expansion is mirrored by growth in the numbers and types of users of networks from the researcher to the home user.Today, computer networks are the core of modern communication. The scope of communication has increased significantly in the past decade and this boom in communications would not have been possible without the progressively advancing computer network.NETWORKING METHODSNetworking is a complex part of computing that makes up most of the IT Industry. Without networks, almost all communication in the world would cease to happen. It is because of networking that telephones, televisions, the internet, etc. work.One way to categorize computer networks are by their geographic scope, although many real-world networks interconnect Local Area Networks (LAN) via Wide Area Networks (WAN). These two (broad) types are:LOCAL AREA NETWORK (LAN)A local area network is a network that spans a relatively small space and provides services to a small amount of people. Depending on the amount of people that use a Local Area Network, a peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities. These can be classified into two types: Single-service servers, where the server performs one task such as file server, print server, etc.; while other servers can not only perform in the capacity of file servers and print servers, but they also conduct calculations and use these to provide information to clients (Web/Intranet Server). Computers are linked via Ethernet Cable, can be joined either directly (one computer to another), or via a network hub that allows multiple connections.Historically, LANs have featured much higher speeds than WANs. This is not necessarily the case when the WAN technology appears as Metro Ethernet, implemented over optical transmission systems.WIDE AREA NETWORK (WAN)A wide area network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is the largest network in the world. The PSTN (Public Switched Telephone Network) also is an extremely large network that is converging to use Internet technologies, although not necessarily through the public Internet.A Wide Area Network involves communication through the use of a wide range of different technologies. These technologies include Point-to-Point WANs such as Point-to-Point Protocol (PPP) and High-Level Data Link Control (HLDC), Frame Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical Network). The difference between the WAN technologies is based on the switching capabilities they perform and the speed at which sending and receiving bits of information (data) occur.WIRELESS NETWORKS (WLAN, WWAN)A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area networkIn order for communication to take place between computers, mediums must be used. These mediums include Protocols, Physical Routers and Ethernet, etc. This is covered by Open Systems Interconnection which comprises all the processes that make information transport possible.The network topology defines the way in which computers, printers, and other devices are connected. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions. Commonly referred to as a linear bus, all the devices on a bus topology are connected by one single cable.

Resource sharing

Resource sharing

One of the intended aspects of wireless grids is that it will facilitate the sharing of a wide variety of resources. These will include both technical as information resources. The former being bandwidth, QoS, and web services, but also computational power and data storage capacity. Information resources can include virtually any kind of data from databases and membership lists to pictures and directories.

Ad-hoc resource sharing between mobile devices in the wireless grid require for the devices to agree on sharing/communication protocols without the existence of dedicated servers.

Coordination Systems

Coordination Systems are the actual mechanisms that enable the sharing of resources between different devices. For different resources, devices use different coordination systems. Examples of such mechanisms are: Samba or NFS for sharing disk space and the distributed.net client for sharing processor cycles.

Trust Establishment

Before users are willing to share any resource, they demand a certain amount of trust between them and the users and/or systems they share resources with. The amount of trust required depends on the kind of information/resource that is to be shared. Sharing processor cycles requires less substantial trust then the sharing of personal information and commercial information can require another level of trust establishment altogether. There are systems currently in operation that can provide a certain amount of trust like the public key infrastructure that makes use of certificates; now often used in web based email systems, and Kerberos.

Resource discovery

Before any resource on a device in the grid can be utilized, those resources that are available must be discovered; all the devices that make up the grid and the resources they possess have to be identified. When a client enters the grid, such as a PDA, it has to be able to communicate to the other users that it is a PDA and it has a camera, GPS capabilities, a telephone function and various office applications such as a text editor. Protocols like UPnP and ZeroConf can detect a new node in the network when it enters. When detected, other users can send a query to the new device to find out what it has to offer. Commercial service providers can 'advertise' the resources they have to offer through IP multicasts. Within large grids containing thousands of nodes, a kind of 'friend of a friend' mechanism can be used. There is a myriad of standards that include resource description protocols. Standards as IETF's ZeroConf, Microsoft's UPnP, the Grid Resource Description Language (GRDL), the Web Services Description Language (WSDL) for describing various specific web services and parts of QoS that describe bandwidths all offer devices a way to describe and publish their specific resources and needs. There are also various different systems currently available that can gather these resource descriptions and structure them for other devices to use. The OpenGrid Services Architecture (OGSA) uses a Web service-style IndexService. The Web services community has defined UDDI which can makes a database of services that are available on the network, and JXTA uses ZeroConf to identify resources in a network. However, the problem with using these in wireless grids is that no stable publisher of these descriptions may exist.

Resource description

For any device to be able to use any resource, a way to identify and describe the resource has to be agreed on by all available devices. If, for instance, storage capacity is to be shared, it first has to be clear what the capacity of each device is and what the storage need is. As said, there are many techniques to describe certain resources but there is not one technique that is able to provide this service for all resources. The available techniques combined, however, cover most of what is needed.

TCP Multiplexing

TCP Multiplexing

TCP Multiplexing is loosely based on established connection pooling techniques utilized by application server platforms to optimize the execution of database queries from within applications. An ADC establishes a number of connections to the servers in its pool and keeps the connections open. When a request is received by the ADC from the client, the request is evaluated and then directed to a server over an existing connection. This has the effect of reducing the overhead imposed by establishing and tearing down the TCP connection with the server, improving the responsiveness of the application.

Some ADN implementations take this technique one step further and also multiplex HTTP and application requests. This has the benefit of executing requests in parallel, which enhances the performance of the application.

TCP Optimization

There are a number of RFCs which describe mechanisms for improving the performance of TCP. Many ADN implement these RFCs in order to provide enhanced delivery of applications through more efficient use of TCP.

The RFCs most commonly implemented are:

* Delayed Acknowledgements [4]
* Nagle Algorithm [5]
* Selective Acknowledgements[6][7]
* Explicit Congestion Notification ECN[8][9]
* Limited and Fast Retransmits[10][11]
* Adaptive Initial Congestion Windows[12]

VIEWS OF NETWORKS

VIEWS OF NETWORKS

Users and network administrators often have different views of their networks. Often, users that share printers and some servers form a workgroup, which usually means they are in the same geographic location and are on the same LAN. A community of interest has less of a connotation of being in a local area, and should be thought of as a set of arbitrarily located users who share a set of servers, and possibly also communicate via peer-to-peer technologies.Network administrators see networks from both physical and logical perspectives. The physical perspective involves geographic locations, physical cabling, and the network elements (e.g., routers, bridges and application layer gateways that interconnect the physical media. Logical networks, called, in the TCP/IP architecture, subnets , map onto one or more physical media. For example, a common practice in a campus of buildings is to make a set of LAN cables in each building appear to be a common subnet, using virtual LAN (VLAN) technology.Both users and administrators will be aware, to varying extents, of the trust and scope characteristics of a network. Again using TCP/IP architectural terminology, an intranet is a community of interest under common administration, usually in the same enterprise. An extranet creates a community of interest that spans multiple enterprises and usually involves multiple administrators, but is not accessible by arbitrary users of the public Internet.Informally, the Internet is the set of users, enterprises,and content providers that are interconnected by Internet Service Providers (ISP). From an engineering standpoint, the Internet is the set of subnets, and aggregates of subnets, which share the registered IP address space and exchange information about the reachability of those IP addresses using the Border Gateway Protocol. Typically, the human-readable names of servers are translated to IP addresses, transparently to users, via the directory function of the Domain Name System (DNS).Over the Internet, there can be business-to-business (B2B), business-to-consumer (B2C) and consumer-to-consumer (C2C) communications. Especially when money or sensitive information is exchanged, the communications are apt to be secured by some form of communications security mechanism. Intranets and extranets can be securely superimposed onto the Internet, without any access by general Internet users, using secure Virtual Private Network (VPN) technology.

Wireless mesh network

Wireless mesh network

A wireless mesh network is a mesh network implemented over a wireless network system such as wireless LAN.

Whereas the Internet is mostly a wire-based, cooperative electronic communication infrastructure similar to the international postal agreement, in that messages are mutually delivered and relayed among their separate domains free of charge, mesh is a wireless cooperative communication infrastructure among a massive number of individual wireless transceivers (i.e. a wireless mesh) that all have network routing capabilities.

Network Structure

Architecture

* Infrastructure wireless mesh networks: Mesh routers form an infrastructure for clients.
* Client wireless mesh networks: Client nodes constitute the actual network to perform routing and configuration functionalities
* Hybrid wireless mesh networks: Mesh clients can perform mesh functions with other mesh clients as well as accessing the network through mesh routers.

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 needs only transmit as far as the next node. Nodes act as repeaters to transmit data from nearby nodes to peers that are too far away to reach, resulting in a network that can span large distances, especially over rough or difficult terrain. Mesh networks are also extremely 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 simply find another route. Extra capacity can be installed by simply adding more nodes.

Applications

Mesh networks may involve either fixed or mobile devices. The solutions are as diverse as communications in difficult environments such as emergency situations, tunnels and oil rigs to battlefield surveillance and high speed mobile video applications on board public transport or real time racing car telemetry.

Operation

The principle is similar to the way packets travel around the wired Internet — data will hop from one device to another until it reaches a given destination. Dynamic routing capabilities included in each device allow this to happen. To implement such dynamic routing capabilities, each device needs to communicate its routing information to every device it connects with, "almost in real time". Each device then determines what to do with the data it receives — either pass it on to the next device or keep it. The routing algorithm used should attempt to always ensure that the data takes the most appropriate (fastest) route to its destination.

Multi-radio mesh

The choice of radio technology for wireless mesh networks is crucial. In a traditional wireless network where laptops connect to a single access point, each laptop has to share a fixed pool of bandwidth. With mesh technology and adaptive radio, devices in a mesh network will only connect with other devices that are in a set range. The advantage is that, like a natural load balancing system, the more devices the more bandwidth becomes available, provided that the number of hops in the average communications path is kept low.

Radio Techniques

* New modulation scheme
o In order to achieve higher transmission rate, new wideband transmission schemes other than OFDM and UWB are needed.

* Advanced antenna processing
o Advanced antenna processing including directional, smart and multiple antenna technologies must be further investigated, since their complexity and cost are still too high for wide commercialization.

* Flexible spectrum management
o Tremendous efforts on research of frequency-agile techniques are required for their practical use.

* media access control
o Cross-layer research also should be further investigated, so as to best utilize the advanced features provided by the physical layer.

Protocols

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

* DSDV (Destination-Sequenced Distance-Vector Routing)
* AODV (Ad-hoc On Demand Distance Vector)
* B.A.T.M.A.N. (Better Approach To Mobile Adhoc Networking)
* PWRP (Predictive Wireless Routing Protocol)
* DSR (Dynamic Source Routing)
* OLSR (Optimized Link State Routing protocol)
* OORP (OrderOne Routing Protocol) (OrderOne Networks Routing Protocol)
* TORA (Temporally-Ordered Routing Algorithm)
* HSLS (Hazy-Sighted Link State)

The IEEE is developing a set of standards under the title 802.11s to define an architecture and protocol for ESS Mesh Networking.

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