A quick post to mention the many current developments in wireless, mainly around the mode without infrastructure: the Ad-Hoc. This mode is used mainly to connect two computers together (peer to peer) for file shares. But there it is to connect hosts to gradually establish a network, allowing all hosts to communicate with each other.
These types of networks have been named in different ways and somewhat confuse the reader. Among the quantity of terms describing the wireless ad-hoc type, I tried to see a little clearer. It often includes the words "MESH AD-HOC WIFI "to describe wireless networks without centralized structure.
Mesh, English word or mesh netting, applies to the topology (architecture) of a network where all hosts of the network (wired or not) are connected to the next, without central hierarchy, thus forming a net-shaped structure. This helps avoid sensitive issues, which in case of failure, eliminate the connection of part of network. If a host is out of order, its neighbors will go through another route. Architecture developed by the U.S. military.
Ad-Hoc, is defined here as "spontaneous" and applies connection type. That is to say that a PC that connects to a network-like ad-hoc network is gone instantly.
Wifi, indicates the type of wireless connection, but other technology could be used.
The basic principle is that each host becomes a router for the others. I would come back a little further on the routing protocols used.
This type of network does not require access point, no dedicated router and dynamically manages the association and disassociation of the hosts. Main strengths: speed of implementation, cost, independence from the access point (that either from commercial or technical). The downside is the need for a mesh size if a job wants to connect it to "hook" a neighbor. Of course we must increase the range of antennas, and ensure that posts are in ongoing activity (sleep to the sound of the fan of your PC). This type of network adapts to all types of terminals: detector, webcam, radio transmission and computer course. Solutions are being tested including the MIT-Roofnet (Massasuchet Institute of Technology), Cambridge (U.S.): Universities, research centers (such Inria), corporations (Ozone) and many Associations (wireless) are working and developing wireless networks without access points (hot spots), that is to say in ad-hoc mode. For future applications are numerous: in the military (of course they have the pepete for) in the field of relief and emergency services (setting up a field hospital ...) and in the civilian sector (connected Internet broadband networks citizens ...), many cities are developing wireless ad hoc networks, even NASA is developing a wireless communication system for ad-hoc exploration vehicles on Mars.
History and technical
MANET:
The early research on networks "Ad-Hoc multihop" (Ad-Hoc multihop network) dates back to 60 by the DARPA (Defense Advanced Reseach Projects Agency) and yes even the U.S. Army!
Today most routing protocols specific connections and mobile ad-hoc group from the MANET (Mobile Adhoc NETwork) established by the IETF in 1997.
A MANET is defined by mobile nodes, with one or more wireless interfaces and have routing function. This routing function allows a packet to reach its destination node to node without router designated. On the other hand, the network is dynamic because nodes can move and change constantly topology.
The building blocks that make up a MANET routing protocol are:
-view (partial or complete) of the topology of the network through an exchange of packets between neighbors ctrl.
-an algorithm for calculating road (MRCA: Mathematical Route Calculation Algorithm) for finding the best path.
-time route calculation to determine the new roads as far in advance as possible.
The main families of routing protocols: the proactive, reactive and hybrid.
- The proactive (Table driven) compute routes in advance, allowing the transfer faster. Each node updates one or more routing tables by control packets. This allows him to have a network topology continuously. Through the dissemination of control packets lowers bade bandwidth. Main
proactive protocol OLSR (Optimized Link State Routing) protocol link-state inspired hyperlan1. It limits diffusion excessive control packets using specialized nodes (multipoint relays) which are responsible for distributing these messages. - Reagents (On Demand), unlike precedents, does not calculate routing before there was a request by an application for a transmission. When a source node desires to transmit to another, it sends a request across the network. After receiving the request, the destination node returns a reply packet that goes back to the source, thus making the route to transfer data
The bandwidth is greater, but the delay between the request and the creation of the road is so important that the package (on hold) is destroyed by the IP layer. To solve this annoying problem, the network layer has been modified to take into account the waiting time. Main
reactive protocol: AODV (Ad-hoc On Demand Distance Vector), distance vector protocol. When a node tries to transmit, if it has no route to its destination in its routing table, it sends a RREQ (Route Request) on the network which will broadcast from host to destination host or until a node with a route to the destination. During this phase, each node receiving this RREQ, will record (in cache) the address of the node having sent the request. Arriving at the final node, it sends a RREP (Route Response) to the source the best path. The answer goes back from node to node through the address stored in the cache. AODV handles disconnections if a node detects that one of his neighbors did not respond, it sends a RERR (Route Error) to the source. - hybrids, mixing the two. They use a technique proactive in a small perimeter around the source (nbe quite small jumps) and reactive nodes farther away. Protocol ZRP (Zone Routing Protocol), protocol CBRP (Cluster Based Routing Protocol).
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