mesh networks a.k.a “ad-hoc”. definition a local area network that employs either a full mesh...
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DefinitionDefinition
A local area network that employs either a A local area network that employs either a full mesh topology or partial mesh full mesh topology or partial mesh topologytopologyFull mesh topology- each node is Full mesh topology- each node is connected directly to each of the othersconnected directly to each of the othersPartial mesh topology- some nodes are Partial mesh topology- some nodes are connected to all the others, but some of connected to all the others, but some of them are only connected to nodes with them are only connected to nodes with which they exchange the most datawhich they exchange the most data
HistoryHistory
Originally sponsored by the Department of Originally sponsored by the Department of Defense for military useDefense for military use
Goal was to provide packet-switched Goal was to provide packet-switched network in mobile elements of a battlefield network in mobile elements of a battlefield in an infra-structureless environmentin an infra-structureless environment
Used a combination of ALOHA and CSMA Used a combination of ALOHA and CSMA and distance vector routingand distance vector routing
Full Mesh TopologyFull Mesh Topology
Every node has a circuit connecting it to Every node has a circuit connecting it to every other node in the networkevery other node in the network
Yields greatest redundancy, so if one node Yields greatest redundancy, so if one node fails, network traffic can be redirected to fails, network traffic can be redirected to any of the other nodesany of the other nodes
Usually reserved for backbone networks Usually reserved for backbone networks since it is very expensivesince it is very expensive
Partial Mesh TopologyPartial Mesh Topology
Some nodes are organized in a full mesh Some nodes are organized in a full mesh scheme but others are only connected to 1 scheme but others are only connected to 1 or 2 in the networkor 2 in the network
Common in peripheral networks Common in peripheral networks connected to a full meshed backboneconnected to a full meshed backbone
Less expensive to implementLess expensive to implement
Yields less redundancyYields less redundancy
Wired meshWired meshIt is possible to have a fully wired mesh It is possible to have a fully wired mesh network, however this is very expensivenetwork, however this is very expensive
AdvantagesAdvantages ReliableReliable Offers redundancyOffers redundancy
DisadvantagesDisadvantages- Expensive- large number of cables and - Expensive- large number of cables and
connections requiredconnections required
Wireless MeshWireless Mesh
Definition- a wireless co-operative Definition- a wireless co-operative communication infrastructure between communication infrastructure between multiple individual wireless tranceivers that multiple individual wireless tranceivers that have Ethernet capabilitieshave Ethernet capabilities
Can either be centralized for highly Can either be centralized for highly scalable applications, or can be scalable applications, or can be decentralizeddecentralized
AdvantagesAdvantages Reliable- each node is connected to several others; Reliable- each node is connected to several others;
when a node fails its neighbors find other routeswhen a node fails its neighbors find other routes Scalable- capacity can be added simply by adding Scalable- capacity can be added simply by adding
nodesnodes Nodes act as repeaters to transmit data from nearby Nodes act as repeaters to transmit data from nearby
nodes to peers too far away to reach- this results in a nodes to peers too far away to reach- this results in a network that can span large distances over rough network that can span large distances over rough terrainterrain
Each node only transmits as far as the next nodeEach node only transmits as far as the next node
How does it work?How does it work?
Data hops from one device to another until Data hops from one device to another until it reaches its destinationit reaches its destination
Each device communicates its routing Each device communicates its routing information to every device it connects information to every device it connects withwith
Each device then determines what to do Each device then determines what to do with received data- pass it on or keep itwith received data- pass it on or keep it
Types of ProtocolsTypes of Protocols
Pro-active- distribute routing tables to the Pro-active- distribute routing tables to the network periodically to maintain fresh lists network periodically to maintain fresh lists of destinationsof destinations
DisadvantagesDisadvantages Wasted bandwidth for transmitting routing Wasted bandwidth for transmitting routing
tablestables Maintains routes that will never be usedMaintains routes that will never be used Some algorithms never converge in large Some algorithms never converge in large
networksnetworks
Re-active- also known as On-Demand Re-active- also known as On-Demand these protocols find routes on demand by these protocols find routes on demand by flooding the network with Route Request flooding the network with Route Request packetspackets
DisadvantagesDisadvantages Delays in finding routesDelays in finding routes Excessive flooding can lead to network Excessive flooding can lead to network
cloggingclogging
Example: ADDVExample: ADDV
ADDV- Ad-hoc On-demand Distance ADDV- Ad-hoc On-demand Distance VectorVector
Establishes a route to a destination only Establishes a route to a destination only on demandon demand
Contrast to the most popular pro-active Contrast to the most popular pro-active protocolsprotocols
How does ADDV work?How does ADDV work?
Network is silent until a connection is Network is silent until a connection is neededneeded
The network node that needs a connection The network node that needs a connection broadcasts a connection requestbroadcasts a connection request
Other nodes forward the message and Other nodes forward the message and record the node they heard it from, record the node they heard it from, creating temporary routes back to the creating temporary routes back to the needy nodeneedy node
When a node that already has a route to When a node that already has a route to the desired node gets the message it the desired node gets the message it sends a message back through the sends a message back through the temporary route to the requesting nodetemporary route to the requesting node
The needy node then uses the route with The needy node then uses the route with the least hops to connectthe least hops to connect
FailuresFailures
When a node fails, a routing error is When a node fails, a routing error is passed back to the transmitting node and passed back to the transmitting node and the process repeatsthe process repeats
Also, note that unused entries in the Also, note that unused entries in the routing tables are recycled after a time, so routing tables are recycled after a time, so unused paths are not keptunused paths are not kept
DrawbacksDrawbacks
More time to establish a connectionMore time to establish a connection
Initial communication to establish a route Initial communication to establish a route is heavyis heavy
Hierarchical- network orders itself into a Hierarchical- network orders itself into a tree or other hierarchy and sends requests tree or other hierarchy and sends requests through the structurethrough the structure
Example: Order One Network Example: Order One Network ProtocolProtocol
The network orders itself into a treeThe network orders itself into a tree
Each node periodically sends “hello” to its Each node periodically sends “hello” to its neighborsneighbors
Each neighbor tells how many neighbors and Each neighbor tells how many neighbors and connections it has and who its “mother” node isconnections it has and who its “mother” node is
Each node picks the node with the largest Each node picks the node with the largest access to links to be its “mother” nodeaccess to links to be its “mother” node
When two nodes pick each other as “mother” When two nodes pick each other as “mother” nodes, that is the top of the treenodes, that is the top of the tree
RoutingRouting
When a node needs a connection with another node and When a node needs a connection with another node and a route doesn’t exist it sends a request to its “mother” a route doesn’t exist it sends a request to its “mother” nodenodeThis node then forwards the message to its “mother” This node then forwards the message to its “mother” node and so on until the original node is connected at node and so on until the original node is connected at the root to the node it wantedthe root to the node it wantedNext the algorithm tries to “cut corners” to optimize the Next the algorithm tries to “cut corners” to optimize the pathpath
Each node on the route floods its neighbors with routing Each node on the route floods its neighbors with routing requestsrequests
When a faster route is found, the unused part of the previous When a faster route is found, the unused part of the previous route is erased and flooding ceases on that routeroute is erased and flooding ceases on that route
AdvantagesAdvantages
Produces fairly good routes while reducing Produces fairly good routes while reducing the number of messages required to keep the number of messages required to keep the network connectedthe network connected
Uses only small amounts of memory at Uses only small amounts of memory at each nodeeach node
The network has a reliable way to The network has a reliable way to establish that a node is not in the networkestablish that a node is not in the network
DisadvantagesDisadvantages
Central “mother” nodes have an extra Central “mother” nodes have an extra burdenburden
Eventually ceases to be scalableEventually ceases to be scalable
Link propagation time establishes a limit Link propagation time establishes a limit on the speed the network can find its rooton the speed the network can find its root
May use more power and bandwidth than May use more power and bandwidth than other link-state protocolsother link-state protocols