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Mesh Networks. A.k.a “ad-hoc”. Definition. A local area network that employs either a full mesh topology or partial mesh topology Full mesh topology- each node is connected directly to each of the others

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mesh networks

Mesh Networks

A.k.a “ad-hoc”

definition
Definition
  • A local area network that employs either a full mesh topology or partial mesh topology
  • Full mesh topology- each node is connected directly to each of the others
  • Partial 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
history
History
  • Originally sponsored by the Department of Defense for military use
  • Goal was to provide packet-switched network in mobile elements of a battlefield in an infra-structureless environment
  • Used a combination of ALOHA and CSMA and distance vector routing
full mesh topology
Full Mesh Topology
  • Every node has a circuit connecting it to every other node in the network
  • Yields greatest redundancy, so if one node fails, network traffic can be redirected to any of the other nodes
  • Usually reserved for backbone networks since it is very expensive
partial mesh topology
Partial Mesh Topology
  • Some nodes are organized in a full mesh scheme but others are only connected to 1 or 2 in the network
  • Common in peripheral networks connected to a full meshed backbone
  • Less expensive to implement
  • Yields less redundancy
wired mesh
Wired mesh
  • It is possible to have a fully wired mesh network, however this is very expensive
  • Advantages
    • Reliable
    • Offers redundancy

Disadvantages

- Expensive- large number of cables and connections required

wireless mesh
Wireless Mesh
  • Definition- a wireless co-operative communication infrastructure between multiple individual wireless tranceivers that have Ethernet capabilities
  • Can either be centralized for highly scalable applications, or can be decentralized
slide11
Advantages
    • Reliable- each node is connected to several others; when a node fails its neighbors find other routes
    • Scalable- capacity can be added simply by adding nodes
    • Nodes 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 terrain
    • Each 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 it reaches its destination
  • Each device communicates its routing information to every device it connects with
  • Each device then determines what to do with received data- pass it on or keep it
types of protocols
Types of Protocols
  • Pro-active- distribute routing tables to the network periodically to maintain fresh lists of destinations
  • Disadvantages
    • Wasted bandwidth for transmitting routing tables
    • Maintains routes that will never be used
    • Some algorithms never converge in large networks
slide15
Re-active- also known as On-Demand these protocols find routes on demand by flooding the network with Route Request packets
  • Disadvantages
    • Delays in finding routes
    • Excessive flooding can lead to network clogging
example addv
Example: ADDV
  • ADDV- Ad-hoc On-demand Distance Vector
  • Establishes a route to a destination only on demand
  • Contrast to the most popular pro-active protocols
how does addv work
How does ADDV work?
  • Network is silent until a connection is needed
  • The network node that needs a connection broadcasts a connection request
  • Other nodes forward the message and record the node they heard it from, creating temporary routes back to the needy node
slide18
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 node
  • The needy node then uses the route with the least hops to connect
failures
Failures
  • When a node fails, a routing error is passed back to the transmitting node and the process repeats
  • Also, note that unused entries in the routing tables are recycled after a time, so unused paths are not kept
drawbacks
Drawbacks
  • More time to establish a connection
  • Initial communication to establish a route is heavy
slide21
Hierarchical- network orders itself into a tree or other hierarchy and sends requests through the structure
example order one network protocol
Example: Order One Network Protocol
  • The network orders itself into a tree
  • Each node periodically sends “hello” to its neighbors
  • Each neighbor tells how many neighbors and connections it has and who its “mother” node is
  • Each node picks the node with the largest access to links to be its “mother” node
  • When two nodes pick each other as “mother” nodes, that is the top of the tree
routing
Routing
  • When a node needs a connection with another node and a route doesn’t exist it sends a request to its “mother” node
  • This 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 wanted
  • Next the algorithm tries to “cut corners” to optimize the path
    • Each node on the route floods its neighbors with routing requests
    • When a faster route is found, the unused part of the previous route is erased and flooding ceases on that route
advantages
Advantages
  • Produces fairly good routes while reducing the number of messages required to keep the network connected
  • Uses only small amounts of memory at each node
  • The network has a reliable way to establish that a node is not in the network
disadvantages
Disadvantages
  • Central “mother” nodes have an extra burden
  • Eventually ceases to be scalable
  • Link propagation time establishes a limit on the speed the network can find its root
  • May use more power and bandwidth than other link-state protocols
where is it going
Where is it going?
  • What is the future of wireless ad-hoc?
  • Automata