Mesh NetworksA.k.a ad-hoc

DefinitionA local area network that employs either a full mesh topology or partial mesh topologyFull mesh topology- each node is connected directly to each of the othersPartial mesh topology- some nodes are connected to all the others, but some of them are only connected to nodes with which they exchange the most data

HistoryOriginally sponsored by the Department of Defense for military useGoal was to provide packet-switched network in mobile elements of a battlefield in an infra-structureless environmentUsed a combination of ALOHA and CSMA and distance vector routing

Full Mesh TopologyEvery node has a circuit connecting it to every other node in the networkYields greatest redundancy, so if one node fails, network traffic can be redirected to any of the other nodesUsually reserved for backbone networks since it is very expensive

A full mesh topology

Partial Mesh TopologySome nodes are organized in a full mesh scheme but others are only connected to 1 or 2 in the networkCommon in peripheral networks connected to a full meshed backboneLess expensive to implementYields less redundancy

A partial mesh topology

Wired meshIt is possible to have a fully wired mesh network, however this is very expensiveAdvantagesReliableOffers redundancyDisadvantages- Expensive- large number of cables and connections required

Wireless MeshDefinition- a wireless co-operative communication infrastructure between multiple individual wireless tranceivers that have Ethernet capabilitiesCan either be centralized for highly scalable applications, or can be decentralized

AdvantagesReliable- each node is connected to several others; when a node fails its neighbors find other routesScalable- capacity can be added simply by adding nodesNodes act as repeaters to transmit data from nearby nodes to peers too far away to reach- this results in a network that can span large distances over rough terrainEach node only transmits as far as the next node

Gizmo truck

How does it work?Data hops from one device to another until it reaches its destinationEach device communicates its routing information to every device it connects withEach device then determines what to do with received data- pass it on or keep it

Types of ProtocolsPro-active- distribute routing tables to the network periodically to maintain fresh lists of destinationsDisadvantagesWasted bandwidth for transmitting routing tablesMaintains routes that will never be usedSome algorithms never converge in large networks

Re-active- also known as On-Demand these protocols find routes on demand by flooding the network with Route Request packetsDisadvantagesDelays in finding routesExcessive flooding can lead to network clogging

Example: ADDVADDV- Ad-hoc On-demand Distance VectorEstablishes a route to a destination only on demandContrast to the most popular pro-active protocols

How does ADDV work?Network is silent until a connection is neededThe network node that needs a connection broadcasts a connection requestOther nodes forward the message and record the node they heard it from, creating temporary routes back to the needy node

When a node that already has a route to the desired node gets the message it sends a message back through the temporary route to the requesting nodeThe needy node then uses the route with the least hops to connect

FailuresWhen a node fails, a routing error is passed back to the transmitting node and the process repeatsAlso, note that unused entries in the routing tables are recycled after a time, so unused paths are not kept

DrawbacksMore time to establish a connectionInitial communication to establish a route is heavy

Hierarchical- network orders itself into a tree or other hierarchy and sends requests through the structure

Example: Order One Network ProtocolThe network orders itself into a treeEach node periodically sends hello to its neighborsEach neighbor tells how many neighbors and connections it has and who its mother node isEach node picks the node with the largest access to links to be its mother nodeWhen two nodes pick each other as mother nodes, that is the top of the tree

RoutingWhen a node needs a connection with another node and a route doesnt exist it sends a request to its mother nodeThis node then forwards the message to its mother node and so on until the original node is connected at the root to the node it wantedNext the algorithm tries to cut corners to optimize the pathEach node on the route floods its neighbors with routing requestsWhen a faster route is found, the unused part of the previous route is erased and flooding ceases on that route

AdvantagesProduces fairly good routes while reducing the number of messages required to keep the network connectedUses only small amounts of memory at each nodeThe network has a reliable way to establish that a node is not in the network

DisadvantagesCentral mother nodes have an extra burdenEventually ceases to be scalableLink propagation time establishes a limit on the speed the network can find its rootMay use more power and bandwidth than other link-state protocols

Where is it going?What is the future of wireless ad-hoc?Automata

Basically, full mesh and partial mesh, but well talk more about these later1972- Packet Radio NetworkWanted soldiers, tanks, aircraft, etc. to be the nodes in the networkSee how all the nodes are connected to every other node. VERY expensive to do this, but yields great redundancyNot really used in practice much, since the whole benefit of using mesh is in the wirelessThought this was interesting application of wireless. Robot that uses a wireless mesh network to see its environment and interact with it.Extension of CalMesh- ad-hoc network of lightweight, small reconfigurable nodes that self-organize to form a wireless mesh networkUpcoming version will enable mobile to mobile mesh networkingVery device intensive There are many different types of protocols for mesh networks. These are a few of the major ones. Pro-active is the most common Internet routing protocol, finds routing paths independently of usage pathsFrom the name, it is a Distance Vector routing protocol.