Mesh Networks

1. Mesh Networks A.k.a “ad-hoc”

2. 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

3. 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

5. 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

6. A full mesh topology

7. 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

8. A partial mesh topology

9. 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

10. 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

11. 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

12. Gizmo truck

13. 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

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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

20. Drawbacks • More time to establish a connection • Initial communication to establish a route is heavy

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

22. 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

23. 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

24. 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

25. 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

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