Wireless Mesh Network



Wireless Mesh Network (WMN)

A wireless mesh network (WMN) is a mesh network created through the connection of wireless access points installed at each network user's locale. Each network user is also a provider, forwarding data to the next node. The networking infrastructure is decentralized and simplified because each node need only transmit as far as the next node. Wireless mesh networking could allow people living in remote areas and small businesses operating in rural neighborhoods to connect their networks together for affordable Internet connections.
According to networking expert John Shepler, in the near future the Wi-Fi card in your laptop might become an access point in addition to its normal role as network client. In a full mesh topology, every node communicates with every other node, not just back and forth to a central router. In another variation, called a partial mesh network, nodes communicate with all nearby nodes, but not distant nodes. All communications are between the clients and the access point servers. The client/server relationship is the basis for this technology.
In Redmond, Cambridge and Silicon Valley, Microsoft is working on what it calls "self-organizing neighborhood wireless mesh networks." The network is created with a Mesh Connectivity Layer (MCL), which is a loadable Microsoft Windows driver that lets users communicate over a wireless mesh network using Wi-Fi or WiMax services. The driver tricks the computer into thinking it's directly connected to an Internet connection. The software creates a virtual network adapter that the computer interprets as a regular network connection and uses an Internet Engineering Task Force (IETF) protocol called Link Quality Source Routing (LQSR) to route data among computers in the neighborhood.
Reported potential advantages of wireless mesh networks include:
  • Decreased need for Internet gateways
  • Collaborative redundant backup technology, which insures data security in the event of disk failure
  • The ability to configure routes dynamically
  • Lower power requirements, which could potentially be met by low-cost or renewable energy sources
  • Increased reliability: Each node is connected to several other nodes and if one drops out of the network, its neighbors simply find another route. 

Mesh Network

A mesh network is a local area network (LAN) that employs one of two connection arrangements, full mesh topology or partial mesh topology. In the full mesh topology, each node (workstation or other device) is connected directly to each of the others. In the partial mesh topology, some nodes are connected to all the others, but some of the nodes are connected only to those other nodes with which they exchange the most data.
The illustration shows a full mesh network with five nodes. Each node is shown as a sphere, and connections are shown as straight lines. The connections can be wired or wireless.
Mesh Network

A mesh network is reliable and offers redundancy. If one node can no longer operate, all the rest can still communicate with each other, directly or through one or more intermediate nodes. Mesh networks work well when the nodes are located at scattered points that do not lie near a common line.
The chief drawback of the mesh topology is expense, because of the large number of cables and connections required. In some scenarios, a ring network or star network may prove more cost effective than a mesh network. If all the nodes lie near a common line, the bus network topology is often the best alternative in terms of cost.
Wireless Mesh NetworksCommunity-based multi-hop wireless networks is disruptive to the current broadband Internet access paradigm, which relies on cable and DSL being deployed in individual homes. It is important because it allows free flow of information without any moderation or selective rate control. Compared to the large DSL and cable modem systems that are centrally managed, mesh networking is organic — everyone in the neighborhood contributes network resources and cooperates.

Overview

Researchers in Microsoft Research Redmond, Cambridge, and Silicon Valley are working to create wireless technologies that allow neighbors to connect their home networks together. There are many advantages to enabling such connectivity and forming a community mesh network. For example, when enough neighbors cooperate and forward each others packets, they do not need to individually install an Internet "tap" (gateway) but instead can share faster, cost-effective Internet access via gateways that are distributed in their neighborhood. Packets dynamically find a route, hopping from one neighbor's node to another to reach the Internet through one of these gateways. Another advantage is that neighbors can cooperatively deploy backup technology and never have to worry about losing information due to a catastrophic disk failure. A third advantage is that this technology allows bits created locally to be used locally without having to go through a service provider and the Internet. Neighborhood community networks allow faster and easier dissemination of cached information that is relevant to the local community. 
Community-based multi-hop wireless networks is disruptive to the current broadband Internet access paradigm, which relies on cable and DSL being deployed in individual homes. It is important because it allows free flow of information without any moderation or selective rate control. Compared to the large DSL and cable modem systems that are centrally managed, mesh networking is organic — everyone in the neighborhood contributes network resources and cooperates.
However, to realize the community-based goal, one has to solve many challenging problems including; capacity and range enhancement, privacy and security, self-stablizing and multi-path multi-hop routing, auto-configuration, bandwidth fairness, etc. In addition to solving the tough problems, success also depends on spectrum etiquette, business models, and economics. We are investigating some of the fundamental technical problems that continue to remain challenging despite several decades of research in packet radio networks. We have deployed testbed networks in our office buildings and in a local apartment complex.

Software Artifacts & Support

We implement ad-hoc routing and link quality measurement in a module that we call the Mesh Connectivity Layer (MCL). Architecturally, MCL is a loadable Microsoft Windows driver. It implements a virtual network adapter, so that to the rest of the system the ad-hoc network appears as an additional (virtual) network link. MCL routes using a modified version of DSR (an IETF protocol) that we call Link Quality Source Routing (LQSR). We have modified DSR extensively to improve its behavior, most significantly to support link quality metrics.
The MCL driver implements an interposition layer between layer 2 (the link layer) and layer 3 (the network layer). To higher layer software, MCL appears to be just another Ethernet link, albeit a virtual link. To lower layer software, MCL appears to be just another protocol running over the physical link.
This design has several significant advantages. First, higher layer software runs unmodified over the ad-hoc network. In our testbeds, we run both IPv4 and IPv6 over the ad-hoc network. No modifications to either network stack were required. Network layer functionality (for example ARP, DHCP, and Neighbor Discovery) just works. Second, the ad-hoc routing runs over heterogeneous link layers. Our current implementation supports Ethernet-like physical link layers (e.g. 802.11 and 802.3) but the architecture accommodates link layers with arbitrary addressing and framing conventions. The virtual MCL network adapter can multiplex several physical network adapters, so the ad-hoc network can extend across heterogeneous physical links. Third, the design can support other ad-hoc routing protocols as well.

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