Mesh NetworksMesh Networks

A.k.a “ad-hoc”A.k.a “ad-hoc”

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

A full mesh topologyA full mesh topology

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

A partial mesh topologyA partial mesh topology

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

Gizmo truckGizmo truck

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

Where is it going?Where is it going?

What is the future of wireless ad-hoc?What is the future of wireless ad-hoc?

AutomataAutomata